Patent Publication Number: US-11385781-B2

Title: Multi-display alignment through observed interactions

Description:
RELATED APPLICATIONS 
     This application claims the benefit of the filing date of U.S. Provisional Patent Application No. 62/907,197 filed on Sep. 27, 2019, which is hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The disclosure generally relates to aligning multiple displays in multiple display systems. 
     BACKGROUND 
     Often users of computing devices will have multiple display devices connected to their computing devices. For example, a user who works on a mobile computer (e.g., laptop computer, tablet computer, etc.) having a small display will often connect to a larger external display, additionally it is increasingly common for a portable device such as a mobile tablet computer to be used as an additional display for another system (such as Apple&#39;s Sidecar feature for iPads to be used with Mac desktop or Laptops). A user who works from a desktop computer may connect the desktop computer to multiple external displays. These additional displays may be connected via a cable or wirelessly, and, being hand held, their physical position, and thus expected logical arrangement with the other displays might change dynamically. This additional display area makes using the computing device much easier and more efficient when simultaneously working with multiple documents and/or multiple software applications on the computing device. 
     When connecting a second or subsequent display device to a computing device that is already connected to a first display device, the user will often be required to explicitly configure the physical arrangement of the multiple display devices relative to each other so that when the user moves a cursor, window, or other graphical object, from one display device to another, or leaves an object spanning across multiple displays, the object moves smoothly and continuously from display to display as expected (e.g., the object moves as if it were a physical object leaving one edge of one display and appearing on the physically adjacent display along the path of the cursor movement at the expected location on the destination display device) and/or the spanning object is aligned as expected across the multiple displays. In one of the typical ways of configuring the relative positions and/or alignment of multiple displays in a multiple display system, the computing device can present on one of the display devices graphical representations of the multiple display devices connected to the computing device. The user can then provide input to arrange the graphical representations of the display devices such that the representations mimic the physical alignment and/or relative positions of the actual, physical display devices. The computing device can then use the arrangement of the graphical representations of the display devices to determine how to align the display buffers for the display devices and/or how move a cursor from one display to another. 
     SUMMARY 
     In some implementations, a computing device can perform multi-display alignment through observed user interactions. The computing device can receive user input aligning a first alignment object on a first display device with a second alignment object on a second display device. With knowledge of the displays&#39; characteristics such as resolution, pixels density, physical size, height of display off table surface, the computing device can use the observed interaction data to solve for and align the display buffers for each display device based on the positions of the alignment objects in each display buffer corresponding to each display device. The alignment itself may consist of scaling, rotation, and translation operations providing a transformation from a large, continuous, virtual rendering space to the pixels in the individual displays. Alternately the alignment might be used to translate the cursor and other graphical objects from display to display in a physically analogous manner without requiring a continuous extended desktop to exist. 
     In some implementations, the computing device can align display buffers based on observed movements of the use attempting to move graphical objects between multiple display devices. When the user intends to move an object from one display to another, they will naturally drag the object in the direction of where they want to place it on the second display thus providing valuable information regarding the physical relationship between the displays otherwise unknown to the system. When display buffers corresponding to the display devices are misaligned, the object may leave the first display where the user dragged it, but the system may cause the object to emerge on the second display in a location different from where the user anticipated potentially causing the user to correct the path of the graphical so as to reach the intended target on the new display. The computing device can detect the correction, as a deviation in trajectory after the object transferred to the second display from the user&#39;s initial arc on the first display, and align the display buffers of the display devices so that graphical objects are presented at the appropriate locations when moved between the display devices. 
     Particular implementations provide at least the following advantages. Multiple display devices (e.g., the display buffers thereof) can be more accurately or precisely aligned thereby improving the user experience when interacting across multiple displays. Multiple display devices can be dynamically aligned without requiring the user to perform a specific or explicit alignment process or interaction. Display alignments can be refined over time by analyzing multiple user interactions across multiple display devices. Changes in display alignment due to display angle, laptop positioning, the user&#39;s position, or other changes, can be dynamically detected and alignment adjustments made without the user having to perform a prescribed alignment interaction or input. By dynamically monitoring interaction, re-solving for position, aligning the display buffers, and cursor/object transformations in a multiple display system, the system can improve the user experience by presenting graphical objects at user expected locations when moving graphical objects across multiple display devices. 
     Details of one or more implementations are set forth in the accompanying drawings and the description below. Other features, aspects, and potential advantages will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram of an example system for multi-display alignment through observed user interactions. 
         FIG. 2  is a diagram illustrating aligning display buffers for multiple display devices. 
         FIG. 3  is a diagram illustrating a display buffer alignment technique using a display alignment model. 
         FIG. 4  is a diagram illustrating aligning display buffers based on a forced user interaction. 
         FIG. 5  is a diagram illustrating various relative display alignments. 
         FIG. 6  illustrates an example graphical user interface for provoking multiple display interaction to determine display alignment. 
         FIG. 7  illustrates an example graphical user interface for observing multiple display interactions to determine display alignment. 
         FIG. 8  is a diagram illustrating a cross-display movement path indicative of misaligned display buffers. 
         FIG. 9  is a diagram illustrating alignment of display buffers based on observed cross-display interactions. 
         FIG. 10  is a diagram illustrating alignment of multiple external display buffers based on observed cross-display interactions. 
         FIG. 11  is a diagram illustrating alignment of multiple external display buffers based on observed cross-display interactions. 
         FIG. 12  is flow diagram of an example process for aligning display buffers based on a forced user interaction. 
         FIG. 13  is a flow diagram of an example process for aligning display buffers based on observed interactions. 
         FIG. 14  is a block diagram of an example computing device that can implement the features and processes of  FIGS. 1-13 . 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     The disclosure generally relates to aligning multiple displays in multiple display systems into a common extended desktop space, or independent spaces, both potentially transferring the cursor from display to display based on the display&#39;s physical size and location so that the cursor logically and visually continuously tracks movement jumping from display to display according to the physical location (similar to a user pointing a laser pointer directly at the display). However, to achieve this, many pieces of precision information are required including: the number of pixels on the display, the special pixel density (might be asymmetric too), the height of the display off the desktop, the physical location and orientation of the displays. While there exist primitive mechanisms for users to describe the display arrangement relationships to the system, they are cumbersome and imprecise leading to less than optimal results which then deteriorate as the physical positioning changes over time without the user fine-tuning the arrangement process. This disclosure describes a mechanism to automatically glean and fine tune these relationships by observing how the user interacts with the system. 
       FIG. 1  is a block diagram of an example system  100  for multi-display alignment through observed user interactions. In some implementations, system  100  can include user device  102 . For example, user device  102  can be a computing device, such as a desktop computer, laptop computer, tablet computer, laptop computer, smartphone, smartwatch, wearable device, or any other type of computing device. 
     In some implementations, system  100  can include display device  110 . For example, display device  110  can be a physical display device connected to user device  102 . Display device  110  can be integral to user device  102 , such as a built-in display of a laptop computer, smartphone, tablet computer, etc. Display device  110  can be an external display connected to user device  102  by a physical connection, such as a video cable that connects a monitor to a desktop computer. Display device  110  can be the primary display device for user device  102 , for example. 
     In some implementations, system  100  can include display device  130 . For example, display device  130  can be an external display device, such as an external monitor, television, projector, augmented reality display, virtual reality display, headset display, smart glasses, smart watch, or other display device. Display device  130  can be connected to user device  102  through network  120 . For example, network  120  can be a wired (e.g., ethernet) or wireless (e.g., Wi-Fi, Bluetooth, peer-to-peer, etc.) network. Network  120  can represent a direct cable connection between user device  102  and display device  130 . Thus, display device  130  can be connected to user device  102  through a wired or wireless connection. 
     In some implementations, user device  102  can include display controller  104 . For example, display controller  104  can manage the presentation of data, graphics, etc., on one or more connected display devices (e.g., display device  110 , display device  130 , etc.) connected to user device  102 . Display controller  104  can manage a display buffer (e.g., frame buffer, screen buffer, video buffer, etc.) for each display device connected to user device  102 . When presenting video (e.g., including graphical objects, graphical user interfaces, etc.), user device  102  and/or display controller  104  can store data (e.g., a bit map, a pixel map, etc.) defining a video frame to be presented on a display device in the display buffer corresponding to the display device. Frames of video can be generated based on the data in the display buffer and sent to the corresponding display device for presentation, according to well-known mechanisms. For example, display controller  104  can manage display buffer  112  for display device  110 . Display controller  104  can manage display buffer  132  for display device  130 . Each display buffer can be configured according to the specifications of the corresponding display device. For example, display buffer  112  can be configured based on the display capabilities, resolution, screen size, pixel dimensions, etc., of display device  110 . Display buffer  132  can be configured based on the display capabilities, resolution, screen size, pixel dimensions, etc., of display device  130 . 
     When user device  102  (e.g., the operating system, an application, etc.) presents a graphical element (e.g., graphical user interface, text, images, icons, cursor, etc.) on a display, user device  102  can write the graphical element to the appropriate location (e.g., horizontal, vertical pixel location) in the appropriate display buffer. The data in the display buffer can then be sent to the corresponding display device for presentation to the user. By changing the location (x,y pixel location) of the graphical element over time, user device  102  can cause the graphical element to be animated on the corresponding display device. Thus, when a user provides input to move a graphical object (e.g., cursor, alignment object, window, etc.), user device  102  and/or display controller  104  can, in response to the input, change the location of the graphical object in the display buffer according to the user input. 
     When multiple displays are connected to user device  102 , the user may wish to move a cursor and/or other graphical object (e.g., application window, folder, etc.) between the displays. To enable a smooth transition between display devices  110  and display device  130 , display buffer  112  and display buffer  132  can be associated with display alignment data that describes how display buffer  112  and display buffer  132  should be positioned (e.g., left/right, above/below) and/or aligned (e.g., horizontal offset, vertical offset, spacing between displays, etc.) with respect to each other. When configured correctly, this alignment data should correspond to, or represent, how the physical display devices  110  and display device  130  are positioned with respect to each other in the real-world environment. 
     In some implementations, user device  102  can be configured with default alignment data (e.g., including display specifications, typical positioning, typical alignment, etc.) for various models of display devices that may be connected to user device  102 . When user device  102  connects to a display device (e.g., display device  120 , display device  130 , etc.), user device  102  can receive model identification information from the display device and use the model identification information to obtain default alignment data for the connected display device. 
     The default alignment data for each display device (e.g., display device  110 , display device  130 , etc.) can indicate the display dimensions (e.g., 8 inches wide×8.94 inches high), the native resolution (e.g., 2560-by-1600 pixels native resolution), the pixel density (e.g., 227 pixels per inch), the size of the bezels (ie the distance between the addressable display and the physical edge of the enclosure, the default spacing relative to other displays (e.g., 2 inches with the displays displays almost physically touching), the default horizontal or vertical alignment offset relative to other displays or relative to a surface upon which the display is sitting (e.g., 3 inches off the resting surface), and/or a default directional position relative to other displays (e.g., above, below, right, left). For example, the default alignment data for display device  110  may indicate that display device  110  is an integral display of a laptop computer that is 9×8 inches, 227 pixels per inch, 3 inches off the resting surface, and should be positioned to the right of other displays. The default alignment data for display device  130  may indicate that display device  130  is a standalone display that is 18×10 inches, 180 pixels per inch, and 5 inches off the resting surface. Based on this default alignment data, display controller  104  can determine the relative positions of display device  110  and display device  130  and their relative alignment (e.g., display device  110  is to the right of display device  130  and has a −50 pixel vertical offset). 
       FIG. 2  is a diagram  200  illustrating aligning display buffers for multiple display devices. As described above, display controller  104  can determine the relative positions of display buffer  112  and display buffer  132  based on default alignment data. Continuing the example above and represented by configuration  202  in diagram  200 , display controller  104  can determine that the left edge of display buffer  112  is proximate to (e.g., but spaced apart from) the right edge of display buffer  132  because the alignment data for display device  110  indicates that display device  110  should be positioned to the right of display device  130 . Display controller  104  can determine the relative vertical alignment of display buffer  112  and display buffer  132  based on default alignment data. For example, based on the display dimensions, resolution, and/or pixel density data in the default alignment data for display device  110  and display device  130 , display controller  104  can determine the relative vertical alignment display buffer  112  and display buffer  132 . For example, display controller can determine that a specific row of pixels (Y 2 ) in display buffer  112  aligns with (e.g., is at the same height as) a specific row of pixels (Y 1 ) in display buffer  132 . Thus, if Y 1  is 50 and Y 2  is 100, the vertical offset value between display buffer  132  and display buffer  112  is 50. For example, when moving graphical objects from display buffer  112  to display buffer  132 , display controller  104  can subtract 50 from the pixel row index of the location of the graphical object when it leaves display buffer  112  to determine the pixel row placement of the graphical object when it enters display buffer  1321 . When moving graphical objects from display buffer  132  to display buffer  112 , display controller  104  can add 50 to the pixel row index of the location of the graphical object when it leaves display buffer  132  to determine the pixel row placement of the graphical object when it enters display buffer  112 . 
     In other configurations (not shown), display controller  104  may determine that display buffer  112  is to the left of display buffer  132  and determine corresponding rows of pixels (e.g., Y 1 , Y 2 ) in display buffer  112  and display buffer  132  that align display buffer  112  and display buffer  132  vertically. Display controller  104  can then determine the appropriate vertical offset for moving graphical objects between display buffers (e.g., display devices). For example, display controller  104  can apply the appropriate vertical offset to determine where the graphical object should appear when moved from one display to another. 
     In yet other configurations (e.g., configuration  204 ), display controller  104  may determine that display buffer  112  should be placed below (or above) display buffer  132  and determine corresponding columns of pixels (e.g., X 1 , X 2 ) in display buffer  112  and display buffer  132  that align display buffer  112  and display buffer  132  horizontally. Display controller  104  can then determine the appropriate horizontal offset for moving graphical objects between display buffers (e.g., display devices). For example, display controller  104  can apply the appropriate horizontal offset to determine where the graphical object should appear when moved from one display to another. 
     As described above, after determining the relative positions of each of the display devices and/or display buffers in a multiple display system based on the default alignment data, display controller  104  can determine a horizontal and/or vertical alignment offset values for the display buffers that can be used to determine where to present graphical objects (e.g., cursor, windows, etc.) that are moved between display devices. For example, with reference to configuration  202  in diagram  200 , Y 1  may correspond to pixel row  1000  of display buffer  132  while Y 2  may correspond to pixel row  800  of display buffer  112 . Thus, display controller  104  may determine a vertical alignment offset of −200 for transitioning, or moving graphical objects, from display buffer  132  (e.g., display device  132 ) to display buffer  112  (e.g., display device  110 ). For example, when moving a cursor from pixel row  900  of display buffer  132  to display buffer  112 , display controller  104  can determine where to place the cursor in display buffer  112  by subtracting 200 from 900 and placing the cursor at pixel row  700  at the left edge of display buffer  112 . When moving the cursor from display buffer  112  to display buffer  132  the negative of the vertical alignment offset can be used to determine where to place the cursor in display buffer  132 . 
     As another example, with reference to configuration  204  in diagram  200 , X 1  may correspond to pixel column  1200  of display buffer  132  while X 2  may correspond to pixel column  200  of display buffer  112 . Thus, display controller  104  may determine a horizontal alignment offset of −1000 for transitioning, or moving graphical objects, from display buffer  132  to display buffer  112 . For example, when moving a cursor from pixel column  1100  of display buffer  132  to display buffer  112 , display controller  104  can determine where to place the cursor in display buffer  112  by subtracting 1000 from 1100 and placing the cursor at pixel column  100  at the top edge of display buffer  112 . When moving the cursor from display buffer  112  to display buffer  132  the negative of the horizontal alignment offset can be used to determine where to place the cursor in display buffer  132 . 
     After determining the relative horizontal (e.g., right/left) or vertical (top/bottom) position of display buffer  112  and display buffer  132 , display controller  104  can align display buffer  112  with display buffer  132  according to the determined relative horizontal alignment offset and vertical alignment offset determined for display buffer  112  and display buffer  132 . For example, with respect to configuration  202 , display controller  104  can align display buffer  112  to the right of display buffer  132  and adjust the vertical alignment according to the determined vertical offset such that pixel row Y 1  of display buffer  132  is aligned with pixel row Y 2  of display buffer  112 . Thus, when the user moves the cursor (or other graphical object) from display device  130  (e.g., display buffer  132 ) off the right edge of display device  130  at pixel row Y 1 , the cursor will appear on display device  110  at the left edge of display device  110  (e.g., display buffer  112 ) at pixel row Y 2 . Thus, if the default alignment data correctly corresponds to the actual, physical, relative alignment of display device  110  and display device  130 , the cursor will appear in the appropriate (e.g., user expected) location when moved from one display device to another based on the logical physical relationship of the displays, as observed by the user. 
     While the default alignment process is described above with reference to two display devices, a similar process can be performed to determine the relative placement of display buffers corresponding to three or more display devices to enable smooth transitions between multiple displays in a multiple display system. 
     However, in some cases, the default alignment data of display device  110  (e.g., display buffer  112 ) and display device  130  (e.g., display buffer  132 ) may not represent the real-world alignment or relative positions of the two display devices. Thus, user device  102  may be configured to cause the user of user device  102  to engage in a display alignment interaction to determine the actual, real-world relative positions of the display devices in a multiple display system. 
       FIG. 3  is a diagram  300  illustrating a display buffer alignment technique using a display alignment model. For example, the display alignment model can be a two-dimensional or three-dimensional model that represents the geometries and relative positions of the display devices (e.g., display device  110 , display device  130 ) in space. As described above, user device  102  can have default alignment data associated with each display device (e.g., display device  110 , display device  130 , etc.) connected to user device  102 . The default alignment data can be used by user device  102  to determine how to generate the display alignment model and align the display buffers (e.g., display buffer  112 , display buffer  132 , etc.) relative to each other in the model so that user device  102  can present graphical objects (e.g., cursors, windows, etc.) that are moved between display devices (e.g., between display buffers) at the locations where the user would expect the graphical objects to appear on the displays thereby providing smooth transition between displays. For example, the display alignment model can be used to align the display buffers for the display devices into a physically continuous and/or representative mathematical space, as described further below. 
     To achieve this display alignment goal (e.g., a smooth transition, presentation of graphical objects at expected locations, etc.), display controller  104  can generate the display alignment model using a normalized pixel transform buffer  302  (e.g., alignment buffer) to determine how to move graphical objects from one display to another. For example, the normalized pixel transform buffer  302  can define a pixel space that maps display buffers for the connected displays to pixel locations within the normalized pixel transform buffer  302  that represent the real world spacing and/or relative orientations of the connected displays as defined by the default alignment data described above or determined by the observed user interactions described below. 
     The pixel transform buffer  302  can include a pixel map (e.g., two-dimensional array of pixels, three-dimensional array of pixels, etc.) that is sized large enough to include the display buffers associated with each connected display and the relative spacing, orientations, positions, and/or alignments of the connected displays. The pixels of the pixel transform buffer  302  can be of a normalized size. For example, each of the displays connected to user device  102  may have different pixel sizes and/or pixel densities. Each of the pixels in the displays, or display buffers, can be mapped to a pixel, or multiple pixels, in the pixel transform buffer  302  so that an appropriate trajectory, curve, etc., can be determined for moving a graphical object from one display buffer to another using the normalized, consistent pixel size array. Moreover, each pixel in the pixel transform buffer can be mapped to real-world dimensions (e.g., lengths, sizes, distances, etc.) so that the display buffers can be appropriately spaced and the pixels within each display buffer can be mapped to appropriate corresponding pixels in the pixel transform buffer  302 . For example, pixel transform buffer  302  can be used to scale, rotate, translate, warp, or otherwise adjust the alignment of display buffers to account for differences in location, size, curvature, etc., of the various display devices (e.g., including keystone correction in projected displays. 
     For example, if the alignment data (e.g., default or determined) for display device  110  indicates that display device  110  is 3 inches above the surface upon which it is resting, then display buffer  112  can be spaced the pixel equivalent of 3 inches from the bottom of pixel transform buffer  302  (e.g., pixel alignment buffer). Display buffer  112  can be mapped to appropriate pixels within pixel transform buffer  302  so that the size of display buffer  112  is appropriately represented. If the alignment data (e.g., default or determined) for display device  130  indicates that display device  130  is 10 inches above display device  110 , then display buffer  132  can be spaced the pixel equivalent of 10 inches above display buffer  112  corresponding to display device  110  in pixel transform buffer  302 . Display buffer  132  can be mapped to appropriate pixels within pixel transform buffer  302  so that the size of display device  130  (e.g., and display buffer  132 ) is appropriately represented. The alignment data for display device  110  and/or display device  130  may indicate that the horizontal spacing between display device  110  and display device  130  is 5 inches. Thus, display buffer  112  and display buffer  132  can be placed the pixel equivalent of 5 inches apart in pixel transform buffer  302 . Thus, the current relative positions, alignment and spacing of display devices  110  and  132  can be represented using pixel transform buffer  302 . 
     In some implementations, pixel alignment buffer  302  can be used to determine how to move graphical objects from one display buffer (e.g., and corresponding display device) to another display buffer. For example, the pixel transform buffer  302  can represent a two-dimensional (or three-dimensional) grid or graph that can be used to calculate the trajectory (e.g., arc, curve, path, etc.) of graphical objects as they are moved from one display buffer (e.g., display buffer  132 ) to another display buffer (e.g., display buffer  112 ), determine errors in the current relative alignments of the various display buffers corresponding to the displays connected to user device  102 , and determine corrections in display buffer alignments, as described below. Based on the relative display buffer positions and alignments represented in the pixel alignment buffer  302 , the trajectories, curves, and alignment corrections can be determined using not only the dimensions or specifications of the represented display devices but also using, or accounting for, the spacings (e.g., empty space) between display devices and/or display buffers and relative display device positions and alignments as represented in pixel transform buffer  302 . 
       FIG. 4  is a diagram  400  illustrating aligning display buffers based on a forced user interaction. For example, in response to detecting a new display device  130  connected to user device  102  which is already connected to display device  110 , display controller  104  can present graphical user interfaces on display devices  110  and  130  that prompt the user to manipulate an alignment object on each display device to indicate the proper physical alignment of each display device. The alignment data received through this user manipulation of the alignment objects can then be used to align the corresponding display buffers so that the appropriate or expected user experience can be achieved when moving graphical objects between display devices. 
     Diagram  400  depicts and/or contrasts the alignment of physical displays (left side of diagram) and display buffers (right side of diagram) in a sequence of stages  404 - 408  over time (indicated by arrow  402 ). Stage  404  represents an example initial alignment of physical displays  110  and  130  versus the alignment of the corresponding display buffers  112  and  132 . The initial alignment can be determined and/or configured by user device  102  when a new display device (e.g., display device  130 ) is detected, for example. The initial alignment can be determined and/or configured by user device  102  based on a previous alignment or based on a default alignment of the display devices/display buffers. For example, user device  102  may receive user input initiating the display alignment procedure described below when the user rearranges the physical displays and needs to realign the display buffers to match the new arrangement of the display devices. 
     Since at stage  404  the buffer alignment may be based on the default alignment data or previous (e.g., old) alignment data, the alignment of display buffers  112  and  132  may not correspond to the actual relative positions and/or alignment of the physical display devices  110  and  130  as configured by the user. For example, at stage  404 , although the physical display devices  110  and  130  are positioned with display device  130  to the left of display device  110  and aligned vertically at their bottom edges, corresponding display buffers  112  and  132  are positioned such that display buffer  132  (corresponding to display device  130 ) is positioned to the right of display buffer  112  (corresponding to display device  110 ) and centered vertically. Thus, because the display buffers  112 / 132  do not have an alignment that matches the real-world alignment of display devices  110 / 132 , graphical objects that are moved between the display devices  110 / 132  may not appear in the appropriate locations on the display device to which the graphical objects are moved. 
     To allow the user to specify the alignment of the display devices  110 / 130 , and correspondingly, the display buffers  112 / 132 , display controller  104  may present graphical object  412  (e.g., alignment object) on display device  130  and graphical object  422  (e.g., alignment object) on display device  110 . Since the data in display buffers  112 / 132  determines what is displayed on each respective display device  110 / 132 , to display the graphical objects on display device  110  and display device  130 , graphical object  422  must also be stored in display buffer  112  and graphical object  412  must be stored in display buffer  132 . 
     At stage  406 , the user can provide input to align the alignment objects on display devices  110  and  130 . For example, the user can provide input, and user device  102  can receive the input, to move the alignment object (e.g., primary alignment object) on the primary display device nearer the alignment object (e.g., secondary alignment object) on the secondary (e.g., newly added) device until the primary alignment object is at the edge of the display device and aligned (e.g., vertically or horizontally) with the secondary alignment object on the secondary display device. While display controller  104  is moving the primary alignment object in the direction specified by the received user input, display controller  104  can move the secondary alignment object in the direction opposite of the user input so that each of the alignment objects move nearer to each other until aligned at the edge of their respective display devices. 
     As illustrated in the example of stage  406 , when display device  110  is the primary display device and display device  130  is the secondary display device, the user can provide input to user device  102  to move graphical object  422  presented on display device  110  toward graphical object  412  presented on display device  130 . As graphical object  422  is moved to the left toward display device  130  and graphical object  412 , display controller  104  can move graphical object  412  to the right toward display device  110  and graphical object  422 . The user can continue providing input to move graphical object  422  until graphical object  422  is at the left edge of display device  110  and aligned vertically with graphical object  412 . Once aligned, the user can provide additional user input (e.g., a mouse click, a button press, etc.) indicating that graphical object  422  is aligned with graphical object  412 . Display controller  104  can receive the user input indicating that the graphical objects are aligned, and determine the display location (e.g., pixel location) of graphical object  422  on display device  110  and determine the display location (e.g., pixel location) of graphical object  412  on display device  130 . 
     During the above alignment interaction of stage  406  using display devices  110  and  130 , graphical objects  422  and  412  are being moved in display buffers  112  and  132 . Since display buffers  112  and  132  are not yet aligned correctly, the movement of graphical objects  412  and  422  may be used to realign the display buffers  112 / 132  to match the real-world alignment of the display devices  110 / 132 . For example, graphical object  422  may move in display buffer  112  according to the alignment user input and correspondingly too how graphical object  422  moves on display device  110 . However, since the display buffers  112 / 132  are not aligned correctly, graphical object  422  in display buffer  112  actually moves away from graphical object  412  and display buffer  132 . Based on the direction of movement of graphical object  422  away from display buffer  132 , display controller  104  can determine that display buffer  112  is positioned on the wrong side of display buffer  132  and rearrange the relative locations of the display buffers  112 / 132  such that display buffer  112  is positioned according to the direction of travel of graphical object  422 . In the example of  FIG. 4 , display controller  104  can reposition display buffer  112  to the right of display buffer  132 , as represented by dashed arrow  430 . 
     Once the relative arrangement (e.g., top, bottom, left, right) of the display buffers is determined, display controller  104  can determine the relative alignment based on the final positions or locations of graphical objects  422  and  412  in display buffer  112  and  132 , respectively. In the example, of  FIG. 4 , since display controller  104  has determined that display buffer  112  should be positioned to the right of display buffer  132  based on the user input, when the display controller  104  receives the additional user input specifying the final positions of graphical objects  422  and  412 , display controller  104  can use the vertical positions (e.g., pixel row indexes) to align display buffers  112 / 132  vertically. If the display buffers were arranged above/below each other, then display controller  104  could use the horizontal positions (e.g., pixel column indexes) of graphical objects  422  and  412  to align display buffers  112 / 132  vertically. For example, at stage  408 , display controller  104  can adjust the vertical position of display buffer  112  (or display buffer  132 ) such that the final locations of graphical objects  422  and  412  are horizontally aligned. In the example of stage  408 , display controller  104  can move display buffer  112  downward relative to display buffer  132  such that graphical objects  422  and  412  are horizontally aligned. Thus, at the end of stage  408 , the arrangement and/or alignment of display buffers  112 / 132  will correspond to, or match, the arrangement and/or alignment of the corresponding display devices  110 / 130  in the real world. 
       FIG. 5  is a diagram  500  illustrating various relative display alignments. While the forced user interaction alignment procedure was described above using an example a horizontal arrangement of displays and vertical alignment adjustments, other display device arrangements and alignments can be determined and corrected using the forced user interaction procedure described above. 
     Diagram  500  includes display device/display buffer arrangement  510 . For example, arrangement  510  is similar to the arrangement of  FIG. 4 . Arrangement  510  can include a primary display device corresponding to display buffer  514  and a secondary (e.g., added) display device corresponding to display buffer  512 . Based on the user input moving graphical objects  516  and  518 , display controller  104  can determine that secondary display device was added to the left of the primary display device and position display buffer  512  to the left of display buffer  514 . Moreover, based on the user input, display controller  104  can determine the respective alignment locations (e.g., pixel rows) of graphical objects  516  and  518  and adjust the vertical position (e.g., up or down offset) of display buffer  512  relative to display buffer  514  so that the alignment locations are aligned horizontally. 
     Diagram  500  includes display device/display buffer arrangement  520 . For example, arrangement  520  is similar to the arrangement of  FIG. 4 . Arrangement  520  can include a primary display device corresponding to display buffer  522  and a secondary (e.g., added) display device corresponding to display buffer  524 . Based on the user input moving graphical objects  526  and  528 , display controller  104  can determine that secondary display device was added to the right of the primary display device and position display buffer  524  to the right of display buffer  522 . Moreover, based on the user input, display controller  104  can determine the respective alignment locations (e.g., pixel rows) of graphical objects  526  and  528  and adjust the vertical position (e.g., up or down offset) of display buffer  524  relative to display buffer  522  so that the alignment locations are aligned horizontally. 
     Diagram  500  includes display device/display buffer arrangement  530 . Arrangement  530  can include a primary display device corresponding to display buffer  534  and a secondary (e.g., added) display device corresponding to display buffer  532 . Based on the user input moving graphical objects  536  and  538 , display controller  104  can determine that secondary display device was added to above the primary display device and position display buffer  524  above display buffer  522 . Moreover, based on the user input, display controller  104  can determine the respective alignment locations (e.g., pixel columns) of graphical objects  536  and  538  and adjust the horizontal position (e.g., right or left offset) of display buffer  532  relative to display buffer  534  so that the alignment locations are aligned vertically. 
     Diagram  500  includes display device/display buffer arrangement  540 . Arrangement  540  can include a primary display device corresponding to display buffer  542  and a secondary (e.g., added) display device corresponding to display buffer  544 . Based on the user input moving graphical objects  546  and  548 , display controller  104  can determine that secondary display device was added to below the primary display device and position display buffer  544  below display buffer  542 . Moreover, based on the user input, display controller  104  can determine the respective alignment locations (e.g., pixel columns) of graphical objects  546  and  548  and adjust the horizontal position (e.g., right or left offset) of display buffer  544  relative to display buffer  542  so that the alignment locations are aligned vertically. 
     Accordingly, the forced user interaction alignment procedure described above can be implemented to align display buffers in a multiple display system such that the arrangement (e.g., relative positions and/or alignment) of the display buffers closely matches or corresponds to the real-world arrangement of the physical display devices. By arranging the display buffers to correspond to the arrangement of the physical display devices, user device  102  and/or display controller  104  can present graphical objects on the display devices when moving the graphical object between display devices according to the user&#39;s expectations. Thus, user device  102  can be configured to avoid frustrating or confusing the user and improve the user experience when working with multiple display devices. 
     While  FIG. 4  and  FIG. 5  describe a forced interaction mechanism for receiving user input specifying the relative positions and alignment of display devices in a multiple display system, display controller  104  may observe other user interactions with user device  102  and the multiple displays connected to user device  102  to dynamically and/or covertly adjust the alignment of display devices in a multiple display system to improve the user experience. For example, these covert adjustments may be performed based on historical user interaction data that describes movements between display devices. The covert adjustments may be performed based on real time or very recent user interaction data that describes movements between display devices. 
       FIG. 6  illustrates an example graphical user interface  600  for provoking multiple display interaction to determine display alignment. In some implementations, GUI  600  can be presented when a changed display arrangement is detected. For example, a change to the current display arrangement can be detected when a new display device is connected to user device  102 . For example, when user device  102 , already connected to display device  110 , detects a new display device  130  connected to user device  102 , user device  102  can present GUI  600  across display device  110  and display device  130 . In particular, since display device  110  was already connected to user device  102 , user device  102  may present graphical object  610  (e.g., a cursor, window, icon, etc.) on display device  110 . For example, user device  102  may present graphical object  610  in the center, or near centered, on display device  110 . To provoke a cross display user interaction, user device  102  can present a prompt  606  on the newly connected display device  130 . For example, prompt  606  may require a user to provide some user input with respect to prompt  606  (e.g., selection of the “ok” button  618 ) to dismiss prompt  606 . Prompt  606  can, for example, be a modal dialog box that simply requires the user to provide input to acknowledge that a new display device has been connected to user device  102  and disallows user interaction with any other graphical element until button  618  is selected. 
     In some implementations, a change to the current display arrangement can be detected using various sensors. For example, a motion sensor attached to a display device (e.g., a laptop computer, a tablet computer, a smartphone, etc.) can detect movement of the display device and cause GUI  600  to be presented. A sound sensor (e.g., microphone) of a computing device can detect a sound associated with moving a display device and cause GUI  600  to be presented. A light sensor can detect a change in ambient light emitted by the current display devices and can cause GUI  600  to be presented. For example, when user device  102 , already connected to display device  110  and display device  130 , detects change to the current display configuration using one or more of the sensors described above, user device  102  can present GUI  600  across display device  110  and display device  130 . In particular, if user device  102  is currently presenting graphical object  610  (e.g., a cursor, window, icon, etc.) on display device  110 , user device  102  can present a prompt  606  on the display device  130  to provoke a cross display user interaction. For example, prompt  606  may require a user to provide some user input with respect to prompt  606  (e.g., selection of the “ok” button  618 ) to dismiss prompt  606 . Prompt  606  can, for example, be a modal dialog box that simply requires the user to provide input to acknowledge that a new display device has been connected to user device  102  and disallows user interaction with any other graphical element until button  618  is selected. 
     In some implementations, the cross-display interaction can be analyzed to determine whether display device  110  and the new display device  130  are arranged and/or aligned correctly. For example, display controller  104  can analyze the trajectory and/or path (e.g., curve, arc, etc.) along which the user has moved graphical object  610  from display device  110  to reach the destination location (e.g., “ok” button  618 ) on display device  130 . Based on the analysis, display controller  104  can determine if the user provided input to correct the path of graphical object  610  when the graphical object was presented on display device  130 . For example, humans typically plan movements involving coordination of multiple joints and degrees of freedom resulting in smooth and continuous arcs. If the user made a corrective input (e.g., indicated by a discontinuity of movement) when moving toward the destination location on display device  130 , display controller  104  can determine that the alignment or arrangement of the display buffer of display device  130  with respect to the display buffer of display device  110  is incorrect. Display controller  104  can analyze the initial path of graphical object  610  on display device  110  to determine how to make the arrangement and/or alignment correction necessary to properly align the display buffers, as described in further detail below. 
       FIG. 7  illustrates an example graphical user interface  700  for observing multiple display interactions to determine display alignment. In some implementations, display controller  104  can observe naturally occurring (e.g., spontaneous, unprovoked, etc.) user interactions with respect to GUI  700  to determine when display buffer alignment adjustments are required for a multiple display system. For example, user device  102  may already be connected to display device  110  and display device  130 . User device  102  can present (e.g., extend) GUI  700  across display device  110  and display device  130 . User device  102  may be presenting graphical object  710 / 720  (e.g., a cursor, window, icon, etc.) on display device  110  or display device  130 . Display controller  104  can determine (e.g., based on a current user interaction, based on historical user interactions) when a user interaction moves between display device  110  and display device  130  and use the cross-display interactions to determine when to correct the alignment of the corresponding display buffers. 
     In some implementations, the cross-display interaction can be analyzed to determine whether display device  110  and display device  130  are arranged and/or aligned correctly. For example, display controller  104  can analyze the trajectory and/or path (e.g., curve, arc, etc.) along which the user has moved graphical object  710  from display device  130  to reach the destination location (e.g., “window” menu item  714 ) on display device  110 . Similarly, display controller  104  can analyze the trajectory and/or path (e.g., curve, arc, etc.) along which the user has moved graphical object  720  from display device  110  to reach the destination location (e.g., “Folder” icon  724 ) on display device  130 . Based on the analysis, display controller  104  can determine if the user provided input to correct the path of graphical object  710 / 720  when the graphical object was presented on the destination display device. If the user made a corrective input when moving toward the destination location on the destination display device, display controller  104  can determine that the alignment or arrangement of the display buffer of display device  130  with respect to the display buffer of display device  110  is incorrect. In some implementations, display controller  104  can analyze the initial path of graphical object  710 / 720  on the originating display device (e.g., display device  130  for graphical object  710 , display device  110  for graphical object  720 ) to determine how to make the arrangement and/or alignment correction necessary to properly align the display buffers of display device  110  and display device  130 , as described in further detail below. 
     Display controller  104  can perform this passive observation and display buffer alignment technique for each cross-display interaction. Display controller  104  can perform this passive observation and display buffer alignment technique periodically on a sampling of historical cross-display interactions. Display controller  104  can perform this passive observation and display buffer alignment technique on a random selection of current or recent cross display interactions. 
       FIG. 8  is a diagram  800  illustrating a cross-display movement path indicative of misaligned display buffers. For example, diagram  800  includes display device  802  and display device  804  that are part of a multiple display system. The user of the system may want to move graphical object  810  (e.g., a cursor) presented on display device  804  to a destination or destination location  816  (e.g., target location) on display device  816 . To cause graphical object  810  to reach destination location  816 , the user can provide input to move graphical object  810  along path  812 . When the display buffers corresponding to display device  802  and display device  804  are aligned correspondingly to the real-world relative positions (e.g., arrangement) of display device  802  and display device  804 , path  812  will typically follow a continuous curve from the starting location of graphical object  810  across display device  804  and across display device  802  to destination location  816 . 
     However, when the display buffers corresponding to display device  802  and display device  804  are not aligned correspondingly to the real-world relative positions (e.g., arrangement) of display device  802  and display device  804 , the user will need to provide input to correct the path  812  of graphical object  810  to reach destination location  816 , as illustrated by the discontinuity  814  in the curve of path  812 . For example, because the display buffers were misaligned, graphical object  810  entered the right edge of display device  802  at too high of a location to continue along the curve corresponding to the path  812  started on display device  804  and the user was required to make a correction (e.g., discontinuity  814 ) to cause graphical object  810  to reach destination location  816 . 
     In some implementations, display controller  104  can detect user corrections to the movement path between display devices to determine when the display buffers for the display devices are misaligned. For example, display controller  104  can analyze path  812  to determine if there are any discontinuities introduced at the destination display device  802  in the curve of the path started on display device  804 . When a discontinuity is found, or detected, display controller  104  can adjust the alignment of the display buffers based on the curve of path  812  started on display device  804 , as described in further detail below. 
       FIG. 9  is a diagram  900  illustrating alignment of display buffers based on observed cross-display interactions. For example, the cross-display user interactions can be provoked (as illustrated by  FIG. 6 ) or passively observed (as illustrated by  FIG. 7 ). The analysis of the paths of the cross-display interactions (e.g., user directed movements of graphical objects from device to device) and adjustments of display buffer alignments can be performed in response to detecting a cross-display interaction, periodically (e.g., nightly, weekly, etc.), in response to detecting specific contexts (e.g., user device is idle, not in use), or a combination thereof. For example, display controller  104  can, on a nightly basis, filter historical user interaction data to identify cross-display interactions occurring during the preceding day. Display controller  104  can analyze the paths of these cross-display interactions to determine whether any user corrections to the paths can be detected. When a user correction is detected, display controller  104  can adjust the relative positions, or arrangement, of the display buffers so that they more closely represent the arrangement of the physical display devices. 
     Diagram  900  illustrates multiple stages  904 ,  906 ,  908  of procedure for aligning display buffers based on observed cross-display user interactions. Each stage shows the physical alignment, or arrangement, of display devices  110  and  130  on the left side of timeline  902  and the virtual alignment, or arrangement, of the corresponding display buffers  112  and  132  on the right side of timeline  902 . 
     The description of diagram  900  starts at stage  904  with misaligned buffers  112  and  132  corresponding to display devices  110  and  130 , respectively. For example, while the display device  130  is physically arranged to the left of display device  110 , the display buffer  132  corresponding to display device  130  is virtually arranged to the right of display buffer  112  corresponding to display device  110 . Moreover, while display devices  110  and  130  are aligned along their bottom edges, display buffers  112  and  132  are centered vertically relative to each other. Thus, the misalignment of the display buffers compared to the physical arrangement of the display devices will cause the user to correct the path of movement when moving graphical objects between display devices  110  and  130 , as described in further detail below. 
     As the user moves graphical object  910  from display device  130  to destination  912  (e.g., target location) on display device  110 , the user will provide input to move graphical object  910  along a smooth path (e.g., arc, curve, trajectory, etc.) toward destination location  912 . For example, the user can indicate destination location  912  by providing some user input, such as mouse click, selection of a graphical object, releasing a graphical object (e.g., when moving a GUI object from one display to another), or other movement termination event that indicates destination location  912 . The process of analyzing a path and realigning display buffers can be performed after receiving the input indicating destination location. For example, the analysis and realignment of display buffers can be performed after the user has confirmed that the user intended to move between display devices, as implied or indicated by the user input at the destination location  912  (e.g., the user&#39;s target) on the second display device  110 . In order to move graphical object  910  across display device  130 , the location of graphical object  910  in display buffer  132  must be updated based on the user input to move graphical object  910  along path  914  so that display buffer  130  can be used by display controller  104  to generate the frames of video presented by display device  130 . 
     In some implementations, display controller  104  can determine the direction of travel of graphical object  910  along path  914  to determine the relative position (e.g., to the right, left, above, below, etc.) of display device  110 . For example, after display controller  104  receives the user input indicating destination location  912  on display device  110 , display controller  104  can analyze the direction of path  914  to determine whether display buffer  112  for the destination display device  110  is on the correct side of display buffer  132 . As depicted at stage  904 , since display device  110  is physical arranged to the right of display  130 , the user will provide input moving graphical object  910  to the right on display device  130  to reach destination location  912 . 
     However, since the display buffer  112  for display device  110  is arranged to the left of display buffer  132 , when graphical object  910  reaches the right edge of display device  130 , the user will have to reverse course and move graphical object  910  to the left off the left edge of display device  130  to cause graphical object  910  to move onto display device  110 /display buffer  112 . If this movement (e.g., the user hitting the edge of the display, moving in the opposite direction, and identifying a destination on another display device) is done within a period of time or near continuously from start location to destination location, display controller  104  can identify this as a corrective movement with respect to relative display positioning and rearrange the relative positions of the display devices. For example, display controller  104  can detect this corrective movement and determine that destination display device (e.g., display device  112 ) is actually located in the initial direction of travel (e.g., to the right) of path  914  on display device  132 . Display controller  104  can then rearrange the relative positions of display buffer  112  and display buffer  132  so that display buffer  112  is to the right of display buffer  132 , as depicted in stage  906 . Thus, when the user subsequently provides input to move graphical object  910  to the right from display device  130  to display device  110 , the graphical object  910  will move to the right off display device  130  and onto display device  110  as expected given the physical orientation of the display devices. Graphical object  910  will show up as expected on display device  110  because the display buffers  112  and  132  are now arranged similar to the relative positions of display device  110  and display device  130 . 
     However, even though the display buffers  112 / 132  may be arranged on the appropriate sides of each other, the display buffers  112 / 132  may not be aligned correctly to produce the expected behavior when graphical object  910  is moved from display device  130  to display device  110  (or vice versa). 
     Referring to stage  906 , a user may provide input to user device  102  to move graphical object  910  from display device  130  to destination location  912  on display device  110 . When initiating the move on display device  130 , the user will typically move graphical object  910  along a path  916  (e.g., a continuous curve) on display device  130  toward destination location  912 . However, when the display buffers for display device  130  and display device  110  (e.g., display buffer  132  and display buffer  112 , respectively) are misaligned, in this case vertically misaligned, with respect to the relative positions of display device  130  and display device  110 , the user will need to provide input correcting the path of graphical object  910  on display device  110  so that graphical object  910  reaches destination location  912  on display device  912 . For example, when display buffer  132  and  112  are misaligned with respect to the relative physical positions of display device  130  and display device  110 , graphical object  910  will appear too low (or too high) on display device  110  (and display buffer  112 ). Thus, the user will need to move graphical object  910  in an upwardly curved path  918  to cause graphical object  910  to reach destination location  912  on display device  110 . The change in trajectory of the initial path  916  creates a discontinuity in the curve of path  916  from display device  130  to destination location  912  on display device  110  that can be used by user device  102  to determine when display buffer  132  and display buffer  112  are misaligned. For example, use device  102  can fit a curve to path  920  (e.g., a curve based on the combination of path  916  and path  918 ) between display buffer  132  and display buffer  112  (e.g., display device  130  and display device  110 , respectively) using well-known curve fitting algorithms. User device  102  can numerically integrate the curve of path  920  and determine if there are any discontinuities. For example, user device  102  can determine if there are any discontinuities in the first derivative or the second derivative of the curve. If a discontinuity in the curve of path  920  is identified, then user device  102  can adjust the relative alignment of display buffer  132  and display buffer  112 . 
     At stage  908 , user device  102  can adjust the relative alignment of display buffer  132  and display buffer  112  based on the curve of initial path  916  on display buffer  132  (e.g., display device  130 ). For example, user device  102  can use the display alignment model of  FIG. 3  to project the curve of initial path  916  beyond the edge of display buffer  132  in the direction of the movement of graphical object  910  (e.g., towards display buffer  912 ). User device  102  can then adjust the alignment of display buffer  112  (e.g., indicated by dashed downward arrow and dashed outline of previous location of display buffer  112 ) so that the destination location  912  indicated by the user is on the projected curve of path  916 . Thus, display buffer  112  can be aligned with display buffer  132  so that the alignment of the display buffers more closely matches the alignment of the physical display devices  130  and  110 . 
     In some implementations, user device  102  can adjust the alignment of display buffers based on multiple user interactions with the display device  110  and display device  130 . For example, a single multi-display user interaction may not provide enough information to correctly align display buffers  112  and  132  to match the physical alignment of display devices  110  and  130 . When display devices  110  and  130  are positioned left and right of each other, as depicted in  FIG. 9 , user device  102  may adjust the relative alignment of display buffer  112  downward with respect to display buffer  132  based on a user interaction but this adjustment may not account for the spacing between display devices. Thus, on a subsequent interaction the user may provide input to correct the input path again when moving between displays because user device  102  did not calculate where to display the graphical object  910  based on a correct spacing between display buffer  112  and display device  132  even though the vertical alignment was previously adjusted. By adjusting the relative alignment of display buffer  112  to fit multiple user interactions (e.g. multiple path curves and corresponding destination locations), user device  102  can adjust the alignment of display buffer  112  up and down (e.g., or left and right if displays are arranged vertically) and the spacing between display buffers  112  and  132  so that for all of the analyzed user interactions, all of the destination locations intersect the corresponding path curves. Thus, adjusting the alignment of the display buffers based on multiple user interactions (e.g., historical user interactions, previous user interactions) may result in a more accurate alignment of the display buffers that more closely represents the actual physical alignment of display devices  110  and  130 . 
       FIG. 10  is a diagram  1000  illustrating alignment of multiple external display buffers based on observed cross-display interactions. For example, diagram  1000  illustrates how a computing device can align external display buffers for multiple external display devices when the external display devices are adjacent. The alignment process illustrated by diagram  1000  can be performed by provoking a user interaction (e.g., presenting GUI targets that the user must select) or by otherwise observing user interactions with graphical object (e.g., GUI targets) on different external displays, as described herein. 
     In some implementations, user device  102  can detect the addition of one or more external display devices  130  and/or  1010  to user device  102  that includes display device  110 . User device  102  can detect an event that may indicate a change in the alignment, orientation, or configuration of the various display devices  130 ,  1010 , and/or  110  with respect to each other. In response to detecting a change in the configuration of the display devices  130 ,  1010 , and/or  110  connected to user device  102 , user device  102  can initiate a provoked (e.g., forced, prompted, etc.) or observed alignment process, as described herein. 
     At stage  1004 , user device  102  can initially align display buffers  1012 ,  132 , and or  112  corresponding to physical display devices  130 ,  1010 , and  110  according to default alignment data or previously determined alignment data, as described above. In the example of stage  1004 , user device  102  can initially align the display buffers with display buffer  1012  on the far left, display buffer  112  on the far right, and display buffer  132  between display buffer  1012  and display buffer  112 . As illustrated by the physical display alignment of display device  130 , display device  1010 , and display device  110 , the initial display buffer alignment may not represent the real-world physical locations of the display devices. For example, the real-world alignment of the display devices may have display device  130  positioned at the far left, display device  110  at the far right, and display device  1010  between (e.g., in the middle of) display device  110  and display device  130 . 
     To align or position the display buffers so that they match the real-world alignment of the physical display devices and will therefore present graphical objects in the appropriate locations on the display devices when the graphical objects are moved between display devices and/or display buffers, user device  102  can perform a display buffer alignment operation based on observed user input (e.g., provoked or passive), as described herein above and below. 
     When performing the provoked or prompted display buffer alignment operation, user device  102  can, in response to detecting a change in display device alignment (e.g., a repositioning or display device addition), present graphical object  1020  (e.g., a cursor, a pointer, an input position indicator, etc.) on one of the display devices (e.g., display device  110 ) and present graphical targets  1022 ,  1024  (e.g., prompts that require user input, prompt  606 , etc.) on the other display devices (e.g., display device  130 , display device  110 . These graphical objects will, of course, be correspondingly represented in display buffers  1012 ,  132 , and  112 . 
     In some implementations, graphical object  1020  can be initially presented on the primary display device (e.g., display device  110 ) when performing the alignment operation. In some implementations, graphical object  1020  can be presented at its current location on a previously connected display device. For example, if user device  102  was previously connected to display device  110  and display device  130  and graphical object  1020  was located on display device  110  when the alignment operation was initiated by user device  102 , then graphical object  1020  can remain presented at its location on display device  110 . 
     In some implementations, graphical targets  1022 ,  1024  (e.g., prompts, passive targets, etc.) can be presented on the other display devices (e.g., display devices  130 ,  1010 , etc.) that are not currently presenting graphical object  1020 . For example, each of the display devices  130 ,  1010  can present one prompt that requests user input. Graphical targets  1022 ,  1024  can be presented at different locations on each display device so that the user will move graphical object  1020  along different trajectories to reach each target. For example, graphical target  1022  can be presented at a different vertical location (e.g., near the top edge of the screen) on display device  130  than the vertical location (e.g., near the bottom edge of the screen) at which graphical target  1024  is presented on display device  1010 . Graphical target  1022  can be presented at a different horizontal location (e.g., near the left edge of the screen) on display device  130  than the vertical location (e.g., near the right edge of the screen) at which graphical target  1024  is presented on display device  1010 . 
     When graphical targets  1022 ,  1024  are presented on display device  120  and display device  1010 , the user may provide input to user device  102  to move graphical object  1020  toward one of the graphical targets  1022 ,  1024 . Since display device  1010  is physically positioned closer to display device  110  than display device  130 , the user will likely move graphical object  1020  from its location on display  110  toward GUI target  1024  on display device  1010 . When graphical object  1020  is moved off the edge (e.g., left edge) of the screen of display device  110 , user device  102  can present graphical object  1020  on the right edge of the screens on display device  130  and display device  1010 . For example, since the user has moved graphical object  1020  to the left off display device  110 , user device  102  can initially determine that display device  130  and/or display device  1010  is positioned to the left of display device  110  and present graphical object  1020  on the right side of the screens of display device  130  and display device  1010 . To be clear, graphical object  1020  will now be presented on both display device  130  and display device  1010 . 
     As the user moves graphical object  1020  on display device  130  and display device  1010  (e.g., the same user input moves graphical object  1020  on both devices), user device  102  can record the trajectory of the movement until the user moves graphical object  1020  to one of the graphical targets  1022  or  1024 . For example, since graphical targets  1022  and  1024  are positioned in horizontally and/or vertically different locations on each display device  130 ,  1010 , the user input moving graphical object  1020  on both devices will not cause graphical object  1020  to intersect both graphical target  1022  and graphical target  1024  at the same time. Thus, when the user moves graphical object  1020  to a graphical target  1022  or  1024  and provides input selecting the graphical target (e.g., an ‘ok’ button, a file, a folder, etc.), user device  102  can determine which display device the user is focused on and align that display device with the display device that initially presented graphical object  1020 . For example, since the location of graphical object  1020  corresponds to the location of graphical target  1024  on display device  1010  when the user input indicating a selection was received, user device  102  can determine that the user&#39;s focus was on display device  1010 . Conversely, since the location of graphical object  1020  corresponds to a location where no graphical target is located (as illustrated by empty circle  1026 ) on display device  130  when the user input indicating a selection was received, user device  102  can determine that the user&#39;s focus was not on display device  1010 . 
     As illustrated in the example of stage  1004 , the user may move graphical object  1020  off the left edge of display device  110  and select graphical target  1024  on display device  1010  since display device  1010  is physically positioned closest to display device  110 . After receiving the user input selecting graphical target  1024 , user device  102  can analyze the path (e.g., trajectory) along which the user moved graphical object  1020  to reach graphical target  1024  (e.g., destination location  1024 ), to determine how to align display buffer  1011  with display buffer  112 , as described above. In this example, since the display buffer  1012  is positioned incorrectly with respect to display buffer  112  and display buffer  132 , user device  102  can reposition display buffer  1012  so that it is adjacent to display buffer  112  and between display buffer  112  and display buffer  132 , as illustrated by the arrow between stage  1004  and stage  1006 . 
     At stage  1006 , user device  102  has aligned display buffer  1012  with display buffer  112  but user device  102  has not yet aligned display buffer  132  with respect to display buffer  1012  and/or display buffer  112 . Thus, the display buffer alignment operation can continue at stage  1006  with graphical object  1020  presented on display device  1010  at the location where graphical target  1024  was previously presented. For example, graphical target  1024  can be dismissed or hidden by user device  102  after being selected by the user. Since graphical target  1022  was not selected by the user, user device  102  can continue to present graphical target  1022  on display device  130 . Seeing the graphical target  1022  (e.g., a user prompt), the user may move graphical object  1020  onto display device  130  to select graphical target  1022 . After receiving user input to move graphical object  1020  to the location of graphical target  1022  and receiving user input selecting graphical target  1022 , user device  102  can align display buffer  132  with respect to display buffer  1012  and/or display buffer  112  based on the path or trajectory along which the user moved graphical object  1020  to reach graphical target  1022  (e.g., the destination location), as described above. Thus, display buffers  112 ,  132 , and  1012  can be aligned by observing how the user moves graphical object  1020  between display devices to select the graphical targets. 
     While the above description of  FIG. 10  primarily describes analyzing a prompted (e.g., provoked) user interaction to align display buffers, a similar approach can be used to align display buffers during an unprompted user interaction. For example, instead of presenting user input prompting graphical targets  1022 ,  1024 , user device  102  can monitor user input that moves graphical object  1020  to passive graphical targets  1022 ,  1024 . For example, passive graphical targets can correspond to menus, files, folders, or other graphical objects that are normally presented on a display screen during normal operation. User device  102  can monitor the user&#39;s movement of graphical object  1020 , receive a user selection input selecting a graphical target, determine which display (e.g., display  1010 , display  130 ) is currently presenting a graphical target (e.g., graphical target  1024 ) at the location where the user selection input was received, and align the corresponding display buffer based on the path along which graphical object  1020  was moved by the user. Thus, display buffers  112 ,  132 , and  1012  can be aligned by observing how the user moves graphical object  1020  between display devices to select the non-prompting graphical targets. 
       FIG. 11  is a diagram  1100  illustrating alignment of multiple external display buffers based on observed cross-display interactions. For example, diagram  1100  illustrates how a computing device can align external display buffers for multiple external display devices when the external display devices are not adjacent. The alignment process illustrated by diagram  1100  can be performed by provoking a user interaction (e.g., presenting GUI targets that the user must select) or by otherwise observing user interactions with graphical object (e.g., targets) on different external displays, as described herein. 
     In some implementations, user device  102  can detect the addition of one or more external display devices  130  and/or  1010  to user device  102  that includes display device  110 . User device  102  can detect an event that may indicate a change in the alignment, orientation, or configuration of the various display devices  130 ,  1010 , and/or  110  with respect to each other. In response to detecting a change in the configuration of the display devices  130 ,  1010 , and/or  110  connected to user device  102 , user device  102  can initiate an observed (e.g., provoked or unprovoked) alignment process, as described herein. 
     At stage  1104 , user device  102  can initially align display buffers  1012 ,  132 , and or  112  corresponding to physical display devices  130 ,  1010 , and  110  according to default alignment data or previously determined alignment data, as described above. In the example of stage  1104 , user device  102  can initially align the display buffers with display buffer  1012  on the far left, display buffer  112  on the far right, and display buffer  132  between display buffer  1012  and display buffer  112 . As illustrated by the physical display alignment of display device  130 , display device  1010 , and display device  110 , the initial display buffer alignment may not represent the real-world physical locations of the display devices. For example, the real-world alignment of the display devices may have display device  1010  positioned at the far left, display device  130  at the far right, and display device  110  between (e.g., in the middle of) display device  130  and display device  1010 . 
     To align or position the display buffers so that they match the real-world alignment of the physical display devices and will therefore present graphical objects in the appropriate locations on the display devices when the graphical objects are moved between display devices and/or display buffers, user device  102  can perform a display buffer alignment operation based on observed user input (e.g., provoked or passive), as described herein above and below. 
     When performing the provoked or prompted display buffer alignment operation, user device  102  can, in response to detecting a change in display device alignment (e.g., a repositioning or display device addition), present graphical object  1120  (e.g., a cursor, a pointer, an input position indicator, etc.) on one of the display devices (e.g., display device  110 ) and present graphical targets  1122 ,  1124  (e.g., prompts that require user input, prompt  606 , etc.) on the other display devices (e.g., display device  130 , display device  110 . These graphical objects will, of course, be correspondingly represented in display buffers  1012 ,  132 , and  112  from which the graphics presented on the displays are obtained and/or generated. 
     In some implementations, graphical object  1120  can be initially presented on the primary display device (e.g., display device  110 ) when performing the alignment operation. For example, in a multiple display system, one of the display devices can be identified as a primary display device. In some implementations, graphical object  1120  can be presented at its current location on a previously connected display device. For example, if user device  102  was previously connected to display device  110  and display device  130  and graphical object  1120  was located on display device  110  when the alignment operation was initiated by user device  102 , then graphical object  1120  can remain presented at its location on display device  110 . 
     In some implementations, graphical targets  1122 ,  1124  (e.g., prompts, passive targets, etc.) can be presented on the other display devices (e.g., display devices  130 ,  1010 , etc.) that are not currently presenting graphical object  1120 . For example, each of the display devices  130 ,  1010  can present one prompt that requests user input. Graphical targets  1122 ,  1124  can be presented at different locations on each display device to induce the user to move graphical object  1120  along different trajectories to reach each target. For example, graphical target  1122  can be presented at a different vertical location (e.g., near the top edge of the screen) on display device  130  than the vertical location (e.g., near the bottom edge of the screen) at which graphical target  1124  is presented on display device  1010 . Graphical target  1122  can be presented at a different horizontal location (e.g., near the left edge of the screen) on display device  130  than the vertical location (e.g., near the right edge of the screen) at which graphical target  1124  is presented on display device  1110 . 
     When graphical targets  1122 ,  1124  are presented on display device  120  and display device  1010 , the user may provide input to user device  102  to move graphical object  1120  toward one of the graphical targets  1122 ,  1124 . Since display device  1010  and display device  130  are both physically located near display device  110 , the user may move graphical object  1120  from its location on display  110  toward GUI target  1124  on display device  1010  or toward GUI target  1122  on display device  130 . In the example of  FIG. 11 , the user has chosen to move graphical object  1120  toward graphical target  1124  presented by display device  1010 . When graphical object  1120  is moved off the edge (e.g., left edge) of the screen of display device  110 , user device  102  can present graphical object  1120  on the right edge of the screens on display device  130  and display device  1010 . For example, since the user has moved graphical object  1120  to the left off display device  110 , user device  102  can initially determine that display device  130  and/or display device  1010  is positioned to the left of display device  110  and present graphical object  1120  on the right side of the screens of display device  130  and display device  1010 . To be clear, graphical object  1020  will now be presented on both display device  130  and display device  1010 . 
     As the user moves graphical object  1120  on display device  130  and display device  1010  (e.g., the same user input moves graphical object  1120  on both display devices), user device  102  can record the trajectory of the movement until the user moves graphical object  1120  to one of the graphical targets  1122  or  1124 . For example, since graphical targets  1122  and  1124  are positioned in horizontally and/or vertically different locations on each display device  130 ,  1010 , the user input moving graphical object  1120  on both devices will not cause graphical object  1020  to intersect both graphical target  1122  and graphical target  1124  at the same time. Thus, when the user moves graphical object  1120  to a graphical target  1122  or  1124  and provides input selecting the graphical target (e.g., an ‘ok’ button, a file, a folder, etc.), user device  102  can determine which display device the user is focused on and align that display device with the display device that initially presented graphical object  1120 . For example, since the location of graphical object  1120  corresponds to the location of graphical target  1124  on display device  1010  when the user input indicating a selection was received, user device  102  can determine that the user&#39;s focus was on display device  1010 . Conversely, since the location of graphical object  1120  corresponds to a location where no graphical target is located (as illustrated by empty circle  1126 ) on display device  130  when the user input indicating a selection was received, user device  102  can determine that the user&#39;s focus was not on display device  1010 . 
     As illustrated in the example of stage  1104 , the user may move graphical object  1120  off the left edge of display device  110  and select graphical target  1124  on display device  1010  since display device  1010 . After receiving the user input selecting graphical target  1124 , user device  102  can analyze the path (e.g., trajectory) along which the user moved graphical object  1120  to reach graphical target  1124  (e.g., destination location  1124 ), to determine how to align display buffer  1012  with display buffer  112 , as described above. In this example, since the display buffer  1012  is positioned incorrectly with respect to display buffer  112  and display buffer  132 , user device  102  can reposition display buffer  1012  so that it is next to display buffer  112  and between display buffer  112  and display buffer  132 , as illustrated by the arrow between stage  1104  and stage  1106  indicating the repositioning of display buffer  1012 . 
     At stage  1106 , user device  102  has aligned display buffer  1012  with display buffer  112  but user device  102  has not yet aligned display buffer  132  with respect to display buffer  1012  and/or display buffer  112 . Thus, the display buffer alignment operation can continue at stage  1106  with graphical object  1120  presented on display device  1010  at the location where graphical target  1124  was previously presented. For example, graphical target  1124  can be dismissed or hidden by user device  102  after being selected by the user. Since graphical target  1122  was not selected by the user, user device  102  can continue to present graphical target  1122  on display device  130 . Seeing the graphical target  1122  (e.g., a user prompt), the user may move graphical object  1120  to display device  130  through display device  110  to select graphical target  1022  as indicated by path  1130 . 
     After receiving user input to move graphical object  1120  to the location of graphical target  1122  and/or receiving user input selecting graphical target  1122 , user device  102  can align display buffer  132  with respect to display buffer  1012  and/or display buffer  112  based on the path or trajectory (e.g., path  1130 ) along which the user moved graphical object  1120  to reach graphical target  1122  (e.g., the destination location), as described above. Thus, display buffers  112 ,  132 , and  1012  can be aligned by observing how the user moves graphical object  1120  between display devices to select the graphical targets. 
     While the above description of  FIG. 11  primarily describes analyzing a provoked (e.g., prompted) user interaction to align display buffers, a similar approach can be used to align display buffers during an unprompted user interaction. For example, instead of presenting user input prompting graphical targets  1122 ,  1124 , user device  102  can monitor user input that moves graphical object  1120  to passive graphical targets  1122 ,  1124 . For example, passive graphical targets can correspond to menus, files, folders, or other graphical objects that are normally presented on a display screen during normal operation. User device  102  can monitor the user&#39;s movement of graphical object  1120 , receive a user selection input selecting a graphical target, determine which display (e.g., display  1010 , display  130 ) is currently presenting a graphical target (e.g., graphical target  1124 ) at the location where the user selection input was received, and align the corresponding display buffer based on the path along which graphical object  1120  was moved by the user. Thus, display buffers  112 ,  132 , and  1012  can be aligned by observing how the user moves graphical object  1020  between display devices to select the non-prompting graphical targets. 
     Example Processes 
     To enable the reader to obtain a clear understanding of the technological concepts described herein, the following processes describe specific steps performed in a specific order. However, one or more of the steps of a particular process may be rearranged and/or omitted while remaining within the contemplated scope of the technology disclosed herein. Moreover, different processes, and/or steps thereof, may be combined, recombined, rearranged, omitted, and/or executed in parallel to create different process flows that are also within the contemplated scope of the technology disclosed herein. Additionally, while the processes below may omit or briefly summarize some of the details of the technologies disclosed herein for clarity, the details described in the paragraphs above may be combined with the process steps described below to get a more complete and comprehensive understanding of these processes and the technologies disclosed herein. 
       FIG. 12  is flow diagram of an example process  1200  for aligning display buffers based on a forced user interaction. For example, process  1200  can be performed by user device  102  in response to detecting a new connection to a new display device. 
     At step  1202 , user device  102 , already connected to a first display device, can establish a connection to a second display device. For example, user device  102  can be a laptop computer with a built-in display that establishes a connection to another display through a video cable. User device  102  can be a desktop computer connected to an external display that establishes a connected to another external display through a video cable. User device  102  can be tablet computer with a built-in display that establishes a wireless connection to a wall mounted display (e.g., television, monitor, etc.). 
     At step  1204 , user device  102  can present a first graphical object the first display device and a second graphical object on the second display device. For example, display controller  104  can present a first graphical object (e.g., a box, a square, an arrow, etc.) on the first display device and a second graphical object (e.g., a box, a square, an arrow, etc.) on the second display device. To do so, display controller  104  can store data representing the first graphical object and the second graphical object in the display buffers for the respective first and second display devices. Frame data can be generated based on the data in the display buffers and the frames can be sent to the display devices according to the respective frame rates of the display devices, according to well-known practices. 
     At step  1206 , user device  102  can receive a first user input for moving the first graphical object on the first display device and the second graphical object on the second display device. For example, display controller  104  can prompt the user to move the first graphical object on the first display device toward the second graphical object on the second display device to align the first and second graphical objects at the edge of their respective display devices. The user can provide input to move the first and second graphical objects using various input devices, such as a mouse, a trackpad, a keyboard, etc. 
     At step  1208 , user device  102  can, in response to receiving the first user input, move the first graphical object on the first display device and the second graphical object on the second display device. For example, display controller  104  can move the first and second graphical objects in the display buffers corresponding to the first and second display devices to cause the first and second graphical objects to appear to move across the first and second display devices according to the receives first user input. For example, if the user provides input to move the first graphical object in one direction (e.g., upward and to the right on the first display device), display controller  104  can move the second graphical object in the opposite direction (e.g., downward and to the left on the second display device) so that at some point in the movement the first and second graphical objects may be aligned. 
     At step  1210 , user device  102  can receive a second user input indicating that a first current location of the first graphical object on the first display device is aligned with a second current location of the second graphical object on the second display device. For example, display controller  104  can receive a second user input (e.g., a mouse click, a particular keyboard input, etc.) indicating that the first and second graphical objects are aligned. For example, the second user input (e.g., a mouse click) can be different than the first user input (e.g., mouse movement) moving the first and second graphical objects. The user may provide the second user input when the first and second graphical objects are horizontally or vertically aligned to indicate that the current locations of the first graphical object and the second graphical objects are aligned in the current physical orientation of the display devices. For example, when the first display device and the second display device are positioned to the left and right of each other, then the user may provide the second user input when the first and second graphical objects are horizontally aligned (e.g., the row of pixels where the first graphical object is located is aligned with the row of pixels where the second graphical object is located). When the first display device and the second display device are positioned above and below each other, then the user may provide the second user input when the first and second graphical objects are vertically aligned (e.g., the column of pixels where the first graphical object is located is aligned with the column of pixels where the second graphical object is located). 
     At step  1212 , user device  102  can, in response to receiving the second user input, align a first display buffer of the first display device with a second display buffer of the second display device based on the first current location and the second current location. For example, display controller  104  can align the display buffer corresponding to the first display device with the display buffer corresponding to the second display device based on the alignment locations on the display devices (e.g., and in the respective display buffers) indicated by the user with the second user input. The alignment can be performed by determining an offset value corresponding to the number of pixel rows or columns between the alignment positions on the respective display devices or within the corresponding display buffers. For example, the number of pixel rows/columns can be determined by calculating the difference in the pixel row/column indices for each alignment location. For example, when the physical display devices (e.g., and display buffers) are positioned above and below each other, the user indicated alignment location for the first graphical object may be at pixel column  20  and the user indicated alignment location for the second graphical object pixel column  75 . Thus, the column offset value for aligning the display buffers can be −50 when moving from the second display buffer to the first display buffer and +50 when moving from the first display buffer to the second display buffer. By adding or subtracting the column offset value to the last location of the graphical object in the previous display buffer of a graphical object being moved between display buffers (e.g., display buffers), display controller  104  can cause the graphical object to appear in the expected location on the destination display device when moving the graphical object between display devices. Similar row offset values can be calculated to align display buffers and move graphical objects between display buffers (e.g., display devices) when the display devices (e.g., display buffers) are arranged to the right and left each other. 
       FIG. 13  is a flow diagram of an example process  1300  for aligning display buffers based on observed interactions. For example, process  1300  can be performed by a display controller  104  on user device  102  to automatically detect and correct alignment issues between display devices (e.g., display buffers) in a multiple display system. Process  1300  can be implemented to covertly or overtly refine the alignment of display buffers so that the display buffer alignment more closely matches the alignment or positioning of the corresponding physical display devices in the real world. When the display buffers more closely match the physical alignment of the display devices, graphical objects moved between display devices are more likely to appear in user expected locations on the display devices thereby improving the user experience. 
     At step  1302 , user device  102  can detect movement of a graphical object from a first display buffer corresponding to a first display device to a second display buffer corresponding to a second display device. For example, as a user provides input to move a graphical object (e.g., cursor, folder, window, etc.) from a first display device connected to user device  102  to a second display device connected to user device  102 , display controller  104  of user device  102  can update the location of the graphical object in the display buffers corresponding to respective display devices. When display controller  104  detects movement of the graphical object between display devices (e.g., from the first display buffer to the second display buffer, or from the second display buffer to the first display buffer), display controller  104  can analyze the movement to determine if an adjustment to the alignment of the display buffers is required. 
     At step  1304 , user device  102  can determine a path corresponding to the movement of the graphical object from a first location in the first display buffer to a second location in the second display buffer. For example, display controller  104  can determine a path along which the user has moved the graphical object from the first location in the first display buffer (e.g., on the first display device) to a second location (e.g., destination location) in the second display buffer (e.g., on the second display device). The second location, or destination location, can be identified by some path terminating action or input taken by the user. For example, the destination location for the path can be identified by user input selecting a graphical object, menu, or some other user input indicative of the target of the movement of the graphical object. 
     In some implementations, user device  102  can exclude paths, or portions of paths, that are not appropriate or valid for use when determining how to align display buffers. For example, if the path on the initial display is wandering (not well described as an arc) then the user possibly lacked intention and the path is consequently not predictive of an alignment issue, nor useful for making an alignment correction. However, if the initial path is not a ballistic arc, it might be an intentional line and then probably very predictive of the intended path to the target and any deviation on the new display is similarly indicative of an alignment error between display buffers. 
     At step  1106 , user device  102  can detect a correction in the path associated with the second display buffer. For example, display controller  104  can fit a curve to the path of the graphical object as it moves between display buffers and determine whether a discontinuity (e.g., correction) exists in the curve of the path. For example, when display controller  104  detects a first or second derivative discontinuity in the curve of the path, display controller  104  can determine that the user made a correction to the path of the graphical object as the user moved the graphical object from the first display buffer to the second display buffer. For example, the discontinuity may be found in the portion of the path corresponding to, or moving across, the second display buffer when the relative positions of the display buffers (e.g., right/left, top/bottom) are correct but the display buffers are misaligned horizontally or vertically. The discontinuity may be found in the portion of the path corresponding to, or moving across, the first display buffer when the relative positions of the display buffers are incorrect (e.g., right/left positions, top/bottom positions, etc.) 
     At step  1308 , user device  102  can adjust a position of the second display buffer relative to the first display buffer based on the detected correction. For example, in response to detecting a correction in the path of the graphical object, display controller  104  can move the position of the second display buffer relative to the first display buffer such that the destination location intersects a projection of the initial path of the graphical object (e.g., the portion of the path before the user correction). Thus, after adjustment, if the user had continued to move the graphical object along the initial path (e.g., a continuous curve extended or projected from the initial path), the graphical object would have reached the destination location without user input correcting the path. 
     The above process  1300  describes an display buffer alignment process that adjusts the alignment of a second display buffer relative to a first display buffer by moving the entire second display buffer such that a destination location intersects a projected or extended curve of an initial portion of a path from a starting location to the destination location. However, process  1300  can be performed using multiple user input path/destination location data sets to more accurately align the display buffers. By aligning the second display buffer such that multiple destination locations intersect multiple corresponding projected user input paths, display controller  104  can more accurately determine not only alignment offsets (e.g., horizontal or vertical alignment), but also spacing between display devices so that display controller  104  can better determine where to location graphical objects in display buffers and on display devices when moving graphical objects between display buffers and display devices. 
     Additionally, the above display alignment approaches could be used to generate different display alignments for different users. For example, by using the forced user interaction approach and/or the observed user interaction approaches described above, the computing device can generate different display alignments for different users that use the same computer and display devices. This may be beneficial when the users have different physical characteristics (e.g., right vs. left hand users, short vs. tall users, etc.) and/or when the users position themselves differently with respect to the display devices when using the computer. 
     Graphical User Interfaces 
     This disclosure above describes various Graphical User Interfaces (GUIs) for implementing various features, processes or workflows. These GUIs can be presented on a variety of electronic devices including but not limited to laptop computers, desktop computers, computer terminals, television systems, tablet computers, e-book readers and smart phones. One or more of these electronic devices can include a touch-sensitive surface. The touch-sensitive surface can process multiple simultaneous points of input, including processing data related to the pressure, degree or position of each point of input. Such processing can facilitate gestures with multiple fingers, including pinching and swiping. 
     When the disclosure refers to “select” or “selecting” user interface elements in a GUI, these terms are understood to include clicking or “hovering” with a mouse or other input device over a user interface element, or touching, tapping or gesturing with one or more fingers or stylus on a user interface element. User interface elements can be virtual buttons, menus, selectors, switches, sliders, scrubbers, knobs, thumbnails, links, icons, radio buttons, checkboxes and any other mechanism for receiving input from, or providing feedback to a user. 
     Example System Architecture 
       FIG. 14  is a block diagram of an example computing device  1400  that can implement the features and processes of  FIGS. 1-13 . The computing device  1400  can include a memory interface  1402 , one or more data processors, image processors and/or central processing units  1404 , and a peripherals interface  1406 . The memory interface  1402 , the one or more processors  1404  and/or the peripherals interface  1406  can be separate components or can be integrated in one or more integrated circuits. The various components in the computing device  1400  can be coupled by one or more communication buses or signal lines. 
     Sensors, devices, and subsystems can be coupled to the peripherals interface  1406  to facilitate multiple functionalities. For example, a motion sensor  1410 , a light sensor  1412 , and a proximity sensor  1414  can be coupled to the peripherals interface  1406  to facilitate orientation, lighting, and proximity functions. Other sensors  1416  can also be connected to the peripherals interface  1406 , such as a global navigation satellite system (GNSS) (e.g., GPS receiver), a temperature sensor, a biometric sensor, magnetometer or other sensing device, to facilitate related functionalities. 
     A camera subsystem  1420  and an optical sensor  1422 , e.g., a charged coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS) optical sensor, can be utilized to facilitate camera functions, such as recording photographs and video clips. The camera subsystem  1420  and the optical sensor  1422  can be used to collect images of a user to be used during authentication of a user, e.g., by performing facial recognition analysis. 
     Communication functions can be facilitated through one or more wireless communication subsystems  1424 , which can include radio frequency receivers and transmitters and/or optical (e.g., infrared) receivers and transmitters. The specific design and implementation of the communication subsystem  1424  can depend on the communication network(s) over which the computing device  1400  is intended to operate. For example, the computing device  1400  can include communication subsystems  1424  designed to operate over a GSM network, a GPRS network, an EDGE network, a Wi-Fi or WiMax network, and a Bluetooth™ network. In particular, the wireless communication subsystems  1424  can include hosting protocols such that the device  100  can be configured as a base station for other wireless devices. 
     An audio subsystem  1426  can be coupled to a speaker  1428  and a microphone  1430  to facilitate voice-enabled functions, such as speaker recognition, voice replication, digital recording, and telephony functions. The audio subsystem  1426  can be configured to facilitate processing voice commands, voiceprinting and voice authentication, for example. 
     The I/O subsystem  1440  can include a touch-surface controller  1442  and/or other input controller(s)  1444 . The touch-surface controller  1442  can be coupled to a touch surface  1446 . The touch surface  1446  and touch-surface controller  1442  can, for example, detect contact and movement or break thereof using any of a plurality of touch sensitivity technologies, including but not limited to capacitive, resistive, infrared, and surface acoustic wave technologies, as well as other proximity sensor arrays or other elements for determining one or more points of contact with the touch surface  1446 . 
     The other input controller(s)  1444  can be coupled to other input/control devices  1448 , such as one or more buttons, rocker switches, thumb-wheel, infrared port, USB port, and/or a pointer device such as a stylus. The one or more buttons (not shown) can include an up/down button for volume control of the speaker  1428  and/or the microphone  1430 . 
     In one implementation, a pressing of the button for a first duration can disengage a lock of the touch surface  1446 ; and a pressing of the button for a second duration that is longer than the first duration can turn power to the computing device  1400  on or off. Pressing the button for a third duration can activate a voice control, or voice command, module that enables the user to speak commands into the microphone  1430  to cause the device to execute the spoken command. The user can customize a functionality of one or more of the buttons. The touch surface  1446  can, for example, also be used to implement virtual or soft buttons and/or a keyboard. 
     In some implementations, the computing device  1400  can present recorded audio and/or video files, such as MP3, AAC, and MPEG files. In some implementations, the computing device  1400  can include the functionality of an MP3 player, such as an iPod™. 
     The memory interface  1402  can be coupled to memory  1450 . The memory  1450  can include high-speed random-access memory and/or non-volatile memory, such as one or more magnetic disk storage devices, one or more optical storage devices, and/or flash memory (e.g., NAND, NOR). The memory  1450  can store an operating system  1452 , such as Darwin, RTXC, LINUX, UNIX, OS X, WINDOWS, or an embedded operating system such as VxWorks. 
     The operating system  1452  can include instructions for handling basic system services and for performing hardware dependent tasks. In some implementations, the operating system  1452  can be a kernel (e.g., UNIX kernel). In some implementations, the operating system  1452  can include instructions for performing display buffer alignment. For example, operating system  1452  can implement the display buffer alignment features as described with reference to  FIGS. 1-13 . 
     The memory  1450  can also store communication instructions  1454  to facilitate communicating with one or more additional devices, one or more computers and/or one or more servers. The memory  1450  can include graphical user interface instructions  1456  to facilitate graphic user interface processing; sensor processing instructions  1458  to facilitate sensor-related processing and functions; phone instructions  1460  to facilitate phone-related processes and functions; electronic messaging instructions  1462  to facilitate electronic-messaging related processes and functions; web browsing instructions  1464  to facilitate web browsing-related processes and functions; media processing instructions  1466  to facilitate media processing-related processes and functions; GNSS/Navigation instructions  1468  to facilitate GNSS and navigation-related processes and instructions; and/or camera instructions  1470  to facilitate camera-related processes and functions. 
     The memory  1450  can store software instructions  1472  to facilitate other processes and functions, such as the display buffer alignment processes and functions as described with reference to  FIGS. 1-13 . 
     The memory  1450  can also store other software instructions  1474 , such as web video instructions to facilitate web video-related processes and functions; and/or web shopping instructions to facilitate web shopping-related processes and functions. In some implementations, the media processing instructions  1466  are divided into audio processing instructions and video processing instructions to facilitate audio processing-related processes and functions and video processing-related processes and functions, respectively. 
     Each of the above identified instructions and applications can correspond to a set of instructions for performing one or more functions described above. These instructions need not be implemented as separate software programs, procedures, or modules. The memory  1450  can include additional instructions or fewer instructions. Furthermore, various functions of the computing device  1400  can be implemented in hardware and/or in software, including in one or more signal processing and/or application specific integrated circuits. 
     To aid the Patent Office and any readers of any patent issued on this application in interpreting the claims appended hereto, applicants wish to note that they do not intend any of the appended claims or claim elements to invoke 35 U.S.C. 112(f) unless the words “means for” or “step for” are explicitly used in the particular claim.