Patent Publication Number: US-10318134-B2

Title: Computer interface having a virtual single-layer mode for viewing overlapping objects

Description:
CLAIM OF PRIORITY 
     This application is a continuation of and claims the benefit of priority under 35 U.S.C. § 120 to U.S. patent application Ser. No. 13/773,382, filed on Feb. 21, 2013, now issued as U.S. Pat. No. 9,164,650, which is a continuation of and claims the benefit of priority under 35 U.S.C. § 120 to U.S. patent application Ser. No. 11/892,155, filed on Aug. 20, 2007, now issued as U.S. Pat. No. 8,386,956, which is a continuation of and claims the benefit of priority under 35 U.S.C. § 120 to U.S. patent application Ser. No. 11/530,883, filed on Sep. 11, 2006, which is a continuation of and claims the benefit of priority under 35 U.S.C. § 120 to U.S. patent application Ser. No. 10/689,687, filed on Oct. 22, 2003, now issued as U.S. Pat. No. 7,739,617, which is a continuation-in-part of and claims the benefit of priority under 35 U.S.C. § 120 to U.S. patent application Ser. No. 10/465,855, filed on Jun. 20, 2003, now issued as U.S. Pat. No. 8,127,248, the benefit of priority of each of which is claimed hereby and each of which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention is generally directed to operating systems for computers, and more particularly to a computer-human interface that manages the manner in which multiple overlapping objects are presented to a user. 
     BACKGROUND OF THE INVENTION 
     The increased processing power that becomes available with each new generation of personal computers provides users with greater opportunities to accomplish a variety of different tasks. A user is no longer confined to performing a single task at any given time on a personal computer. Rather, multitasking has become a common manner of operating the computer. Such multitasking may occur within a single application program, e.g., a user might have several documents open within a word processing or graphics program. Likewise, it can occur across multiple applications. For instance, the user could open a web browser to access one or more web sites on the Internet, while at the same time running an electronic mail program to read messages and a word processing program to paste the content of the messages or web sites into one or more documents. 
     In graphical user interfaces that employ windows to present data, each task that is being performed by the user may have one or more windows associated with it. For example, each document that is open in a word processing program will have its contents displayed in a separate window. In addition, various functions performed by the program, such as spell checking, print spooling and the like may each have one or more secondary windows associated with them, to provide status information and/or user input. Similarly, every other application program that is running on the computer presents one or more windows to the user. For instance, if a browser is employed to access a number of different types of web sites, e.g., an http site, an ftp site and a news site, the contents of each site might be presented in a different respective window. 
     It can be appreciated that, as multiple tacks are performed on the computer, the number of windows that are simultaneously displayed can become significant. For the inexperienced user, multiple open windows can be a source of frustration or confusion. More particularly, the windows are presented in a layered manner. Every window has a relative depth associated with it, wherein the most recently accessed, or active, window appears in the foreground of the display, and every other window is located “behind” the active window, in inverse relation to the order in which they were accessed. As a result, a window of interest may become completely overlaid by other, later-accessed windows, thereby blocking it from view. The user may not know how to navigate to the desired window without closing, minimizing, or repositioning all of the windows that overlie it, which may not be consistent with the operation intended by the user. Even for the more experienced user, a large number of open windows may present a cluttered interface which detracts from the ability to easily access desired information in a particular window. 
     One approach to solving this problem is described in co-pending, commonly assigned U.S. application Ser. No. 09/447,419, filed Jan. 4, 2000. In this approach, a single-window viewing mode can be selected, in which a single window, or at most a few windows associated with the currently active task, is displayed to the user. All other windows relating to non-active tasks are automatically minimized, to thereby reduce the amount of information presented to the user at any one time. 
     The present invention is directed to an alternative approach to facilitate navigation among multiple windows of information. More particularly, some users may prefer to keep the windows open for all ongoing tasks, rather than reduce most of them to a minimized state. For instance, it may be desirable to keep multiple windows open to enable their content to be easily copied from one to another. As the number of open windows increases, however, the user&#39;s ability to locate the one containing the desired content becomes more difficult. 
     While the case of overlapping windows readily illustrates the potential for user difficulties, that is not the only situation in which overlapping objects can be a source of inconvenience to the user. For instance, multiple icons in a folder can lie on top of one another, thereby inhibiting the ability of the user to locate one of interest. More generally, almost any type of object that is displayed in a graphical user interface can appear in front of another object, and thereby interfere with the user experience. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a computer-human interface provides a mechanism to manage the available space of a computer display in a manner that facilitates viewing of multiple objects that are overlaid upon one another. The interface includes one or more user-selectable modes in which the objects are rearranged, and resized if necessary, so that the objects can be simultaneously viewed in their entireties within the area of the display, thereby enabling any one of the objects to be easily selected for access. In effect, the presentation of the objects is “flattened” so that all objects appear at the same virtual depth, rather than overlapping one another. Once the desired object has been selected, the display returns to the normal layered view, either automatically or in response to a further user command. With this approach, there is no need to minimize windows, or otherwise manually move objects within the display, in order to access one that is overlaid by another, thereby enabling the user to keep a constant working environment. 
     Further features of the invention, and the advantages attained thereby, are described hereinafter in connection with preferred embodiments of the invention illustrated in the accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a general block diagram of a computer system in which the present invention can be implemented; 
         FIG. 2  is a block diagram showing the relationship of some of the software and hardware components of the computer system; 
         FIGS. 3-8  are screen shots illustrating an example of the effects achieved with the present invention; 
         FIGS. 9-15  depict illustrative examples of one algorithm for repositioning the windows; 
         FIG. 16  is a flowchart summarizing the algorithm; 
         FIG. 17  depicts the use of a border for each window; 
         FIG. 18  illustrates an example of a variation of the invention; 
         FIGS. 19 a -19 d  and 20 a -20 d    are schematic illustrations of operations in the “Show Desktop” viewing mode; 
         FIG. 21  shows an example of the display in the “Show Desktop” mode; 
         FIG. 22  illustrates a panel for choosing user options to select the different viewing modes; and 
         FIGS. 23 a -23 d    are schematic illustrations of the “Application Only” viewing mode. 
     
    
    
     DETAILED DESCRIPTION 
     To facilitate an understanding of the present invention, it is described hereinafter with particular reference to the viewing of multiple open windows on the desktop of a computer display. It will be appreciated, however, that the principles which underlie the invention are not limited to this particular application. Rather, they can be employed in any environment in which multiple objects might overlie one another, and it is desirable for the user to view each of them substantially in their entireties. 
     In addition, various features of the invention are occasionally described in the context of their implementation in the user interface associated with the Macintosh® Operating System (Mac OS®) provided by Apple Computer, Inc. These features are equally applicable to other types of graphical user interfaces. Consequently, specific aspects of the implementation that are described hereinafter should not be viewed as any limitation on the applicability of the invention to a variety of different computer-human interfaces. 
     The present invention is directed to the presentation of objects to a user in a computer system, such as the display of windows, icons, images, etc. The hardware components of a computer system, of a type in which the invention can be implemented, are briefly described herein to provide a thorough understanding of the manner in which the invention operates within the system to produce the desired results. Referring to  FIG. 1 , an exemplary computer system includes a computer  10  having a variety of external peripheral devices  12  connected thereto. The computer  10  includes a central processing unit  14  and associated memory. This memory generally includes a main memory which is typically implemented in the form of a random access memory  16 , a static memory that can comprise a read-only memory  18 , and a permanent storage device, such as a magnetic or optical disk  20 . The CPU  14  communicates with each of these forms of memory through an internal bus  22 . The peripheral devices  12  include a data entry device such as a keyboard  24 , and a pointing or cursor control device  26 , such as a mouse, trackball, pen or the like. One or more display devices  28 , such as a CRT monitor or an LCD screen, provide a visual display of information, including the various components of the graphical user interface. Hard copies of desired information can be provided through a printer  30 , or similar such device. A network connection  31  provides the computer with access to one or more servers, which may function as gateways, file storage systems, messaging systems, and the like. Each of these external peripheral devices  12  communicates with the CPU  14  by means of one or more input/output ports  32  on the computer. 
     A significant component of a user&#39;s experience in operating a computer is the user interface, i.e., the manner in which the computer presents information to the user via the display device  28 . In an effort to make the computing experience as friendly and intuitive to the user as possible, many computer systems employ a graphical user interface. The graphical user interface may constitute an element of the computer&#39;s operating system, as in the case of the Mac OS® and the Windows® operating system provided by Microsoft Corporation. In other cases, the graphical user interface may comprise a separate application program that interacts with the operating system, or one that is integrated with the operating system. 
     One of the fundamental components of most graphical user interfaces is the window. In essence, a window functions as a container for a particular type of data that is to be presented to the user, such as the text in a word processing document, graphical images in a drawing document, or the content of an Internet web page. Each different application program that is being executed on the computer presents its associated data within a separate window. For instance,  FIG. 2  illustrates an example in which three application programs  34 , such as a word processing program, a web browsing program and an electronic mail program, are all running simultaneously on the computer. Some or all of the code for these programs is loaded into the main memory  16 , for access by the CPU  14 . Whenever one of these programs has data to display to the user, it sends a request to the computer&#39;s operating system  36 , requesting a window for the presentation of the data. This request is provided to a window manager  38 , which sends instructions to a display driver  40  to create the structure of the window on the display  28 , and informs the application program of the area within which its data can be displayed. 
     If all three application programs are running concurrently on the computer, three different windows that are respectively associated with the three programs may be displayed. At any given time, one of these windows is the active window, namely the window which pertains to the current task and receives user input from the keyboard  24  and the cursor control device  26 . If the user clicks in one of the other windows to perform a new task, it becomes the active window and the previously active window becomes non-active. The window manager is responsive to the action of the cursor control device  26  to cause the displays of the active and non-active windows to be changed accordingly, for example by dimming features of non-active windows or removing color from their components, and bringing the active window to the forefront of the display. In addition, the window manager is responsive to other user actions to store data for each window. Thus, if the user repositions or resizes a window, that information is stored so that the next time the window is opened, it appears at the size and position last set by the user. 
     It is also possible to open several windows under the control of a single application program. For example, if the user is working with multiple documents in a word processing program, each document is displayed in a separate window. Furthermore, different portions of the same document can be displayed in different respective windows. Consequently, it is conceivable that a significant number of windows can be opened on the computer&#39;s display  28 , particularly for users who perform a number of different tasks on their computers.  FIG. 3  illustrates an example of a computer display containing a variety of windows, which may accumulate as a result of all of the tasks at are performed during a typical day of operating the computer. 
     While the ability to have multiple windows simultaneously open on the computer display is advantageous, since it provides the user with instantaneous access to the information associated with a number of different tasks, in some situations such a display may diminish the user experience. For instance, multiple open windows may inhibit the user&#39;s ability to navigate to a particular item of information that is desired. More specifically, the windows are displayed in a layered environment. As each new window is opened, it appears in the foreground of the display, and may overlap or completely obscure other windows. Similarly, when a previously opened window is accessed and made active, it is brought to the foreground, and may also overlay or obscure other windows. As a result, the least recently accessed window will appear to be “behind” all of the other windows, making it difficult for the user to find. 
     Of course, the user can locate a desired window by closing all of the other windows that are displayed on top of it. However, such an action may be contrary to the user&#39;s intentions, since the closing of a window may effectively terminate the task associated with the information in that window. If the task has not yet been completed, the user may not want to close the window. As an alternative, the user could move all of the windows manually, or minimize them to a designated holding area such as a dock, or hide all of the running applications. However, each of these actions results in a change to the working environment, which may be undesirable. In addition, further effort on the part of the user would be required to restore the environment to its original condition. 
     In accordance with the present invention, these concerns associated with a proliferation of windows are addressed in a user interface that selectively provides a “flattened”, i.e., virtual 2-dimensional, view of the open windows to be viewed. In general, this flattening is accomplished by positioning each open window to be viewed in a respective portion of the total display area, coupled with any resizing that may be required to eliminate overlap of the windows. As a result, the entirety of each window of interest is visible to the user. From this view, the user can easily locate and select any desired window that is open on the display. After the selection takes place, the display is returned to the normal view, with the selected window appearing in the foreground, and all other windows in their previous positions. 
     The effect that is achieved with the present invention is illustrated in the sequence of screen shots depicted in  FIGS. 3-8 . As noted previously,  FIG. 3  illustrates an example of a typical computer display, containing a variety of open windows  42 - 50 . Window  42  is the active window, and therefore appears in the foreground. Since the display presents a layered view of the windows, each of the other windows  44 - 50  appears to be located behind one or more of the other windows. Thus, one attribute of each window is its layer, or depth, relative to the other windows. After completing a task associated with window  42 , the user may desire to access the contents of window  46 . For purposes of illustration, outer edges of window  46  are visible behind window  44 . It may be the case, however, that window  44  is larger than window  46 , as a result of which window  46  would be totally obscured from the user&#39;s view. 
     In accordance with the present invention, the user&#39;s ability to access window  46 , or any other window that is partially or totally obscured, is enhanced by temporarily rearranging the windows into a virtual non-layered, or “flattened” arrangement. To initiate such a viewing mode in one embodiment of the invention, the user might actuate an appropriate control element, e.g. a predetermined key or combination of keys on the keyboard, a control button on one of the windows, a selection from a menu  52 , etc. Alternatively, the user might issue a spoken command. In other embodiments, the indication to enter the alternative viewing mode might come from a source other than the user. For instance, a program might request this mode through an application programming interface (API) call. For example, the operating system, an application program, or other component of the computer system may initiate the alternative viewing mode in response to a certain condition. 
     When this viewing mode is requested, the windows transition from the initial layered view of  FIG. 3  to the flattened, or single-layer, view of  FIG. 5 .  FIG. 4  illustrates an intermediate state as the windows are moving from the multi-layer view of  FIG. 3  to the virtual single-layer view of  FIG. 5 . As can be seen, the windows are moving away from each other, and shrinking in size. This movement preferably occurs over a discernable period of time, so that the user can visualize the transition from the layered view to the flattened view. At the final stage depicted in  FIG. 5 , each of the windows occupies its own space within the area of the display, and without overlap, i.e. their locations are mutually exclusive of one another. To achieve this appearance, the windows are repositioned and reduced in size, if necessary. In addition, the desktop area  51  of the display is preferably darkened, to dim icons and other background objects, and thereby highlight the windows being viewed in this mode. 
     From the virtual single-layer view of  FIG. 5 , the user can easily select a desired window, or an object in any window. For example, the user might select a file in the window  42 , and drag it to a folder in the previously obscured window  46 . To facilitate identity of each window, particularly if they are significantly scaled down in size, a text label can be drawn in the window over which the cursor is positioned. This label (not shown) can display the title or name of the window. 
     Continuing with the illustrated example, the user has selected window  46 , which is depicted in  FIG. 6  by the location of the cursor and the shading. After making the selection, the windows return to their original sizes and positions based on the data maintained in the window manager  38 , as depicted in  FIGS. 7 and 8 , to again present a layered view. The return to this view might be accomplished automatically in response to selecting a window, or may be the result of an affirmative action on the part of the user, e.g. a toggle action on the key or button that was used to initiate the single-layer viewing mode, selecting a command from a menu, actuating a control element in the user interface, etc. Upon returning to the normal layered view, the depth attribute for the selected window  46  has been changed as a result of it having been selected by the user, so that it now appears in the foreground, enabling the user to easily access the contents of this window. 
     The invention takes advantage of the fact that the content of each window is typically buffered in memory associated with the display driver  40 . Thus, all of the pixel data for each window is available to be displayed as portions of overlapping windows are uncovered, thereby avoiding the need to request any data from the applications  34 , or even have them be aware of the alternative viewing mode. However, even if all of the window content is not buffered, the principles of the invention are still applicable. In such a case, a call can be made to the applications to have them redraw the contents of their windows, once they have been repositioned. 
     The functionality of the present invention can reside in a number of different environments. In the case of the exemplary computer system depicted in  FIG. 2 , it might be incorporated into the windows manager. In other cases, it could be embodied in a separate program that operates to lay out application windows or other user interface elements, for instance a plug-in module. It could also be present in an application program. 
     In a preferred embodiment of the invention, when the user initiates the single-layer viewing mode, e.g. by pressing a predetermined function key, the new positions for the windows are calculated in the background, while the windows remain in their original positions. Once the new positions have been determined, the windows then move in a smooth fashion from their original, layered positions to the calculated, non-layered positions. One algorithm for calculating new positions for the windows will be described with reference to an illustrative example depicted in  FIGS. 9-13 . In this example, three windows A, B and C overlap one another in the normal viewing mode, as illustrated in  FIG. 9 . Once the user performs an action to initiate the virtual single-layer viewing mode, the first step in the process is to define the area within which the windows are to be viewed. The total area of the display is indicated by the rectangle  54  in  FIG. 9 . In one embodiment, it may be acceptable to allow the windows to cover this entire area. In other cases, however, it may be more appropriate to restrict the windows from certain portions of the display. For example, it may be desirable to keep the menu bar  52  within view at all times, rather than permit the windows to overlap it. Likewise, the display might contain a dock  56  for storing control elements, minimized windows, or the like. This dock might appear at the bottom of the display, as illustrated in  FIG. 9 , or along one of the sides, and it may be desirable to keep this component in view at all times as well. Taking these considerations into account, a boundary depicted by the rectangle  58  is determined, to define the area within which the windows are permitted to move. 
     Once the boundary  58  has been defined, a target position for each window is determined. In one embodiment of the invention, the algorithm attempts to maintain the relative positioning of the windows, to the extent possible. In this embodiment, therefore, a vector is established for each pair of overlapping windows, which identifies the desired movements of the windows relative to one another. In the example of  FIG. 9 , the vector V AC  indicates the directions of movement of the windows A and C relative to one another. This vector is established by drawing a line between the center points C A  and C C  of each of the two windows. In a similar manner, vectors V AB  and V BC  are established by drawing lines through the center points of each other pair of overlapping windows. 
     For each pair of windows, the amount of overlap is determined in each of horizontal and vertical dimensions. In the example of  FIG. 9 , the horizontal overlap of windows A and B is identified as ΔX AB , and the vertical overlap is ΔY AB . Similarly, the overlap between windows A and C is measured as ΔX AC  and ΔY AC , and the overlap between windows B and C is measured as ΔX BC  and ΔY BC . These delta values represent distances by which the respective windows must move away from each other to eliminate overlap. The dimensions can be measured in units of pixels, for instance, or any other suitable metric. 
     In one implementation of the invention, it is preferable to move each window along the vectors V AC , V AB , etc., to thereby maintain their relative positions, to the extent possible. Consistent with this objective, it is also desirable to move the windows the minimum amount necessary to eliminate overlap. For instance, with reference to  FIG. 10 , it can be seen that two windows D and E have a significant amount of overlap ΔX DE  in the horizontal direction, but a relatively small overlap ΔY DE  in the vertical direction. For example, ΔX DE  may be 20, whereas ΔY DE  may be 3. Once the two windows have moved vertically away from each other by at least 3 pixels, further relative movement between them is unnecessary, even though they may still “overlap” in the horizontal direction, as illustrated in  FIG. 11 . 
     To this end, as a further feature of the invention, once the values for ΔX DE  and ΔY DE  are determined, the smaller value of the two is selected. The value for the other of the two parameters is then calculated as a function of the selected value and the slope of the vector. Thus, in the example given above, where ΔX DE =20 and ΔY DE =3, if it is assumed that the slope of the vector V DE =1.5, then ΔY DE  is maintained at its actual value of 3, since it is the smaller of the two values, and ΔX DE  is set to the adjusted value of 3/1.5=2. 
     These established delta values are then apportioned between the windows in each pair. Referring again to  FIG. 9 , assume that the adjusted value for ΔX AC =12 pixels. In one approach, the values can be equally apportioned between the two windows. In such a case, window A would be assigned a value of Δx A,C =−6, i.e. movement six units to the left, and window C would be assigned a value Δx C,A =+6. In another approach, the amount of movement of each window is weighted in inverse relation to its size, so that a bigger window moves less than a smaller window. If the area of window A is three times larger than that of window C, their relative movements are therefore allocated at a ratio of 1:3. Thus, window A would be assigned a value of Δx A,C =−3, and window C is assigned a value Δx C,A =+9. 
     For overlapping windows A and B, if it is assumed that they have approximately the same area, the ΔX value is equally weighted between them. Thus, if ΔX AB =30, window A is assigned a value of Δx A,B =−15, and window B is assigned a value of Δx B,A =+15. 
     All of the assigned Δx values for a given window are then algebraically summed, to compute a movement value for that window. For the case where weighting is employed, in the preceding example, the horizontal movement value for window A, ΔX A , is therefore ˜18. In the same manner, the vertical movement value ΔY A  is determined. In this case, the component of this value for the overlap between windows A and B, i.e. Δy A,B , will be positive, whereas the component attributable to the overlap between windows A and C, Δy A,C , will be negative. As a result, the composite amount of the vertical movement value is likely to be quite small. In a similar manner, the horizontal and vertical movement values ΔX and ΔY for each of windows B and C are likewise computed. 
     The calculated movement values are then used to determine target positions for the windows. The determination of the target positions for the windows is carried out in an iterative manner. For this purpose, the computed ΔX and ΔY values are multiplied by a suitable moderating factor, and new positions for the windows are calculated in accordance with these moderated amounts. For instance, if the moderating factor is 0.5, after the first iteration each of the three windows will have moved half of the distance necessary to eliminate overlap, as depicted in  FIG. 12 . The foregoing steps are then repeated in a cyclic manner, until the overlap between windows has been eliminated, or at least substantially eliminated. The moderating factor can remain constant for every iteration, or it can be varied to alter the rate at which the windows are moved during the process. For example, a relatively large moderating factor can be employed at the beginning of the process, and then be decreased during later iterations, so that the effective window movement starts out relatively fast, and then slows down as they approach a final state. Conversely, the moderating factor can progress from large to small, so that the window movement starts out slowly, and then accelerates as the degree of overlap begins to diminish. 
     Other conditions can be employed to determine a suitable moderating factor as well. For instance, if there is a significant amount of overlap among windows, as indicated by the largest of the measured delta values, it may be preferable to start off with small increments of movement, to thereby maintain relative positioning. On the other hand, a minimal amount of overlap would permit a larger moderating factor to be employed, to reduce the number of iterations necessary to define the target positions. 
     As another condition, the number of windows to be repositioned can be considered. If the number of windows is small, e.g. two or three, a larger moderating factor can be employed from the outset. Conversely, if the number of windows is large, a smaller moderating factor might be preferable, to avoid the possibility that a small window might “leap frog” over an adjacent window, particularly where weighting is employed. 
     As new positions for the windows are calculated, some of them will approach the boundary  58 . Referring to  FIG. 13 , after several iterations, windows A and B extend beyond the horizontal dimensions of the boundary  58 . To maximize the utilization of the designated display area, therefore, an external force is selectively added to the movement computations. For this purpose, a bounding rectangle  59  is determined for all of the windows. This bounding rectangle also encompasses the boundary  58 . Thus, when all of the windows are contained within the boundary  58 , the bounding rectangle  59  is contiguous with the boundary  58 . However, when any of the calculated positions for the windows extends beyond the boundary, as depicted in  FIG. 13 , the bounding rectangle no longer coincides with the boundary. 
     During each iteration, the aspect ratio of the bounding rectangle  59  is compared with the aspect ratio of the boundary  58 . In the example of  FIG. 13 , the boundary  58  may have an aspect ratio of 5:3, or 1.67, whereas the bounding rectangle may have an aspect ratio of 6:3, i.e. 2. Accordingly, a horizontal external force value is added to the movement vector for each window that extends beyond the boundary  58 . In the example of  FIG. 13 , a positive value would be added to the movement vector for window A, to urge it to the right, and a negative force value would be added to the movement vector for window B. The amount of this force can be a function of the difference in the aspect ratios of the boundary  58  and the bounding rectangle  59 . 
     The foregoing process is carried out for a suitable number of iterations, to incrementally calculate target positions for each of the windows in the flattened viewing mode. The number of iterations could be fixed, or it can vary in dependence upon different factors. For instance, once the overlap has been eliminated among all windows, or it has reached a suitable minimal value, e.g. less than 1% of the window areas, the process can stop. As another condition, it may be desirable to limit the process according to time, so that the user does not have to wait too long between entering the command for the flattened viewing mode and initiation of window movement. 
     It is possible that the windows could reach a “stalemate” position before the final iteration of the process. For instance, during one iteration a window might move slightly to the left, to reduce overlap with a second window. However, that may cause it to overlap a third window or extend beyond the boundary, in which case it might move to the right on the next iterations. In the stalemate condition, therefore, the windows might simply be bouncing in place, rather than moving to non-overlapping positions. To detect such a situation, the position of each window can be averaged over a suitable number of the most recent iterations, e.g. ten iterations. If this moving average does not change over subsequent iterations, steps can be taken to eliminate the stalemate. For instance, the external force can be reduced to permit the windows to move farther outside the boundary in an effort to find optimal positions. 
     As illustrated in the example of  FIGS. 9, 12 and 13 , it may not be possible to completely separate windows A and B and yet maintain them within the boundary  58  if they remain at their original sizes. Accordingly, as a further step, the windows are scaled down in size, if needed.  FIG. 14  illustrates the destination positions for the windows after the final calculations have been made. At this point, a determination is made whether any of the dimensions of the bounding rectangle  59  are greater than those of the boundary  58 . If so, the windows are scaled down in size by an amount corresponding to the ratio of the dimensions of the two rectangles, as depicted in  FIG. 15 . Although only one window may have extended beyond the border, it is preferable to apply the scaling factor to all of the windows, so that they maintain their same relative sizes in the single-layer mode. In addition, the scaling should be proportionately applied in both the horizontal and vertical directions, so as to maintain the configurations, e.g., aspect ratios, of the windows. 
     Once the final destinations and scaling factor have been determined, the windows are then repositioned, and resized as necessary. These actions preferably occur as an animation in which the windows transition from their original positions to the target positions and sizes over a discernable period of time. For instance, the movement and resizing can occur in a linear manner over a period of 2-5 seconds. Thus, the iterative process is transparent to the user, and only a smooth transition from the original position to the alterative view is displayed. 
     The flowchart of  FIG. 16  summarizes one implementation of the general procedure that is carried out in the foregoing process. In response to receipt of a command to change the display to a flattened viewing mode at step  60 , the boundary  58  for the display area is determined at step  62 . This boundary might be calculated during the step, or it might be pre-defined, in which case it is retrieved from memory during step  62 . Thereafter, a list of the overlap deltas is generated for each pair of overlapping windows at step  64 , and a determination is made at step  65  whether all the deltas have a value of zero, i.e. there are no overlapping windows, or some suitable minimum value. If so, the repositioning process can end at that point. If at least two windows overlap, the movement vector for each pair of overlapping windows is determined at step  66 . The smaller of the two deltas for each pair of windows is chosen at step  68 , and an adjusted value is computed for the other delta at step  70 , in accordance with the determined vector. In step  72 , the resulting deltas are then allocated between the windows of each pair, as signed values to indicate right/left or up/down movement. At step  74 , the aspect ratios of the boundary  58  and the bounding rectangle  59  are compared. If they are not equal, an external force value is computed at step  76  for the windows that extend beyond the boundary. The moving averages for the windows are then checked at step  78 , to see if they have been changing. If not, the external force values are reduced, or eliminated, at step  80 . 
     A composite delta value for each window is then calculated at step  82 , and these values are scaled in accordance with the moderating factor in step  84 , to determine the amount and direction of movement for each window. 
     These movement vectors are applied to the current window positions at step  86  to determine new target positions, and the process then returns to step  64 , where the amount of overlap of the windows at the new positions is measured for the next iteration. The process continues to loop through each of steps  64 - 86 , and new target positions are calculated, until a determination is made at step  65  that there are no overlapping windows, or some other terminating condition has been reached. At this point, the destination positions have been identified. 
     Once the destination positions have been calculated in this manner, the size a the bounding rectangle  59  is compared to the boundary  58  in step  88 . If either dimension of the bounding rectangle exceeds that of the boundary, the excess amount is determined and used to compute a scaling factor in step  90 . Then, at step  92 , the windows are moved to the destination positions on the display, and simultaneously resized if necessary in accordance with the scaling factor. 
     The original positions and sizes of the windows are maintained by the Window Manager  38 , however. Subsequently, when the user issues the command to return to the layered view, the windows move back to their original positions and sizes, again, preferably within a discernable time period. If the user has selected a particular window while they were in the flattened view, the Windows Manager changes the relative depth values of the windows accordingly, so that the selected window appears in the foreground when they return to the original positions. If the selected window is a member of a logical group, it may be preferable to bring all of the windows in the group to the foreground. For example, a window group could comprise all of the windows associated with an application. Another type of group might be a primary window and any secondary windows, such as tool palettes, dialog boxes, etc., associated with the primary window. 
     Within this general framework, a number of variations are possible. For example, it may be desirable to add a border to each window, to thereby maintain a gap between them when they are repositioned. For example, as depicted in  FIG. 17 , a border  94  of a suitable number of pixels could be added to the edge of each window  96 . Further in this regard, it is preferable to provide rounded corners on the borders  94 , to thereby enable the windows  96  to slide diagonally past one another. The border can be invisible, or it might be displayed to the user, e.g. to present the appearance of a halo around each window. 
     As another variation, it may be useful to attempt to keep windows from same application together, for example to facilitate cut-and-paste operations. To accomplish such a result, an “attraction” factor can be computed for such windows. For instance, a vector can be established between each pair of windows belonging to the same application, and an attraction value can be computed which would cause them to move along the vector towards each other. This value could to be a function of the distance between the windows, e.g. one-tenth of the distance between their centers. It is included in the algebraic addition of the Δx and Δy values of the windows to calculate their composite movement values. 
     In the example of  FIGS. 3-8 , all open windows on the display are repositioned to be visible and fully accessible, in response to the command that initiates the flattened viewing mode. In variations of this embodiment, additional commands can be included to cause a subset of the open windows to be presented to the user. For example, actuation of a first function key might cause all of the open windows to be repositioned, as shown in  FIGS. 3-8 , whereas actuation of a second function key may cause only those windows associated with the active application to be brought to the foreground and repositioned. In such a case, the windows associated with non-active applications can remain in their original positions, but be dimmed while the active windows are being repositioned. 
     A third function key can be associated with a command that initiates a “Show Desktop” viewing mode. In one embodiment of this mode, all of the windows appear to slide off the display, so that the user can access the icons on the desktop. For example,  FIG. 18  illustrates the windows as they are moving off the display, so that the desktop and its icons become visible. To accomplish this result, the boundary  58  is treated as a stationary window. The foregoing algorithm is then executed to cause all of the other windows to be repositioned to eliminate overlap with this stationary window, which results in their being moved out of the display area. 
     The “Show Desktop” viewing mode facilitates interaction among desktop objects, as well as between desktop objects and open windows. To illustrate,  FIG. 19 a    schematically depicts a situation in which a number of overlapping windows F-K obscure desktop icons  100 . If the user desires to access one of these icons, the “Show Desktop” viewing mode is initiated, for instance by pressing and holding down a predetermined key or combination of keys. As a result, the windows move outside of the boundary  58 , and hence outside of the viewing area, as represented in  FIG. 19 b    by the dashed outlines. In this state, the user can view the desktop icons  100 , select a desired one of them, e.g.  100   a , and drag it to any desired location on the desktop, or onto another icon. Upon releasing the key, the windows return to their original positions within the field of view, i.e., the positions illustrated in  FIG. 19 a   , wherein the icons are once again covered. 
     In a preferred embodiment of the invention, the user can employ the “Show Desktop” viewing mode to transfer information between windows and obscured areas on the desktop. Referring again to  FIG. 19 b   , if the user exits the “Show Desktop” mode while dragging the icon  100   a , e.g. by releasing the third function key, the icon being dragged remains visible on top of the windows, as depicted in  FIG. 19 c   . In this context, the term “drag” does not necessarily mean that the icon is moving while the windows are returning to their original positions. Rather, the user only needs to continue to press the mouse button, or perform a similar action that maintains the selection of the icon while the Show Desktop mode is being exited. Once the windows have returned to their original positions, the user can then continue to drag the icon to any desired window, as shown in  FIG. 19 d   , and drop it into the contents of that window. While the dragging of a single icon is shown in the illustrated example, multiple desktop icons can be selected and dragged to a window as a group. 
     Conversely, while in the normal viewing mode, the user can select and begin dragging an object  100   b  contained in an open window, as shown in  FIG. 20 a   . Upon pressing a key or taking other appropriate action to initiate the “Show Desktop” viewing mode while continuing to drag the object, the open windows disappear from view, but the selected object  100   b  remains visible, as depicted in  FIG. 20 b   . The user can then drop that object onto a desktop icon  100   c , e.g. a disk drive, that was previously obscured by the windows, as shown in  FIG. 20 c   . Thereafter, the windows are returned to their normal positions, as depicted in  FIG. 20   d.    
     Thus, the “Show Desktop” mode enables the user to temporarily remove open windows from view, to provide access to desktop objects obscured by those windows, and then return the windows to their original positions. This operation is easily accomplished without the need to reposition, resize or minimize the windows. In other words, interaction between desktop objects and the contents of windows can be achieved without disturbing the window environment. 
     Alternative techniques for removing the windows to reveal the desktop can be employed. For instance, rather than sliding off the screen, the actuation of the third function key can cause all of the windows to be instantly hidden, or to slowly fade from view, while the key is pressed. Likewise, various forms of 3-dimensional animation might be utilized, such as virtual rotation of the entire screen about an axis that causes the view with the windows to rotate out of sight while the view of the desktop rotates into sight. 
     Rather than completely remove the windows from view in the “Show Desktop” mode, it may be preferable to have an edge of each window remain visible at the border of the display, or to represent the windows by means of tabs or pull-out drawers along the border. As long as the “Show Desktop” mode provides a temporary viewing state where the windows do not obscure the icons  100 , the ability to interact between windows and desktop objects is facilitated. 
       FIG. 21  illustrates one example of this concept. When the user performs the appropriate action to go into the “Show Desktop” mode, a translucent screen border  102  fades into view as the windows move to the edges of the display. The windows do not move all the way off the display screen. Rather, a portion  104  of each window remains visible beneath the border  102 , confirming for the user that the windows have not disappeared. This can be accomplished, for example, by defining the boundary  58  to be contiguous with the interior of the border. As an alternative to any of the other mechanisms for returning to the normal view, or in addition thereto, the user can click on the area of the border  104 , or drag an object such as an icon to the border, which causes the windows to return to their original positions. 
     In the illustrated examples, the “Show Desktop” viewing mode encompasses the entire area of the display. In some cases, it may be preferable to displace only those windows that obscure a predetermined portion of the display. For instance, if the user typically groups icons of interest in a particular area, e.g. in the upper left quadrant or along the right edge, then it is not necessary to remove windows appearing in other areas. In this case, the “Show Desktop” viewing mode might be configured to displace only those windows which appear in a designated portion of the display. This can be accomplished, for example, by dimensioning the boundary rectangle  58  so that it only covers the area of interest, rather than most or all of the display area. 
     While function-keys have been described above as the mechanism for entering the different viewing modes, a number of different approaches can be employed.  FIG. 22  illustrates an example of a preferences panel, or control panel, via which the user can select the appropriate mechanisms. As shown in the lower part of the panel, the user has chosen the right mouse button to select the “All Windows” mode, the left Control button on the keyboard to select the “Application Windows” mode, and the F10 function-key to select the “Show Desktop” mode. 
     In addition to keys and mouse buttons, the user can designate active screen corners to initiate the viewing modes. In operation, when the user positions the cursor in one of the designated corners of the display screen, the selected viewing mode is initiated. In the illustrated example, the upper left corner of the screen has been selected for the “All Windows” mode, and the upper right corner has been designated for the “Application Windows” mode. A menu  106  of available choices is displayed for the lower right corner. From this menu, the user can designate the “Desktop” mode, or a different type of functionality. A particular advantage of using active screen corners lies in the fact that, if the user is attempting to drag an object, such as an icon, to a hidden window, by dragging the object to the active corner the display will automatically switch to the single-layer mode, so that the hidden window will appear and the icon can be dropped onto it. With this approach, the user only has to concentrate on one device during the drag-and-drop operation, namely the mouse or other cursor control device, and move it in a continuous, natural manner. He or she is not required to interrupt the operation to activate a different element, such as a key on the keyboard. 
     Preferably, the user can switch between different single-layer modes. For instance, while in the “Applications Windows” mode, the user can switch the display to the “All Windows” mode by pressing the appropriate key or moving the cursor to the active corner of the screen. When this occurs, the windows that were dimmed in the background are returned to their normal brightness values, and all windows are repositioned in accordance with the foregoing description. In this case, the application windows that were already in the foreground are moved from their current positions in the “Application Windows” mode, rather than returning to their original positions that they occupied before that mode was initiated. Similarly, if the user selects the “Desktop” mode from one of the other single-layer modes, the windows move off the screen from their current positions in that other mode. 
     While in the “Application Windows” mode, the user can switch among the different applications that are currently running.  FIG. 23 a    illustrates an example of a display containing a number of open windows that are associated with different applications. The windows labeled “A” are associated with one application, those labeled “B” are associated with a second application, and those labeled “C” belong to a third application. Upon pressing the second function key or otherwise activating a control element that initiates the “Application Windows” mode, the windows associated with the foreground application, in this case Application A, are repositioned and resized as necessary to present them in a single-layer view, as depicted in  FIG. 23 b   . The windows associated with the other applications remain in their original positions in the background in a dimmed state, represented by the dashed outlines. 
     While in this view, if the user activates a designated control element, e.g. presses the “Tab” key, the display can switch to the windows associated with the application that was most recently active before the Application A. Referring to  FIG. 23 c   , the windows for Application B are brought to the foreground, and repositioned and resized as necessary. At the same time, the windows belonging to Application A are dimmed. They can remain in their single-layer positions, rather than returning to the original positions of  FIG. 23 a   . Each subsequent activation of the control element causes the display to cycle through the windows associated with each of the open application programs, in order of most recently accessed to least recently accessed, or any other suitable order. Thus, as shown in  FIG. 23 d   , the next depression of the Tab key causes the windows of Application C to be presented in the single-layer view. The same control element could also be operative in the “All Windows” mode, to cause the view to switch to the “Application Windows” mode. 
     To enable the foregoing functionality to be achieved, the computer preferably operates in a modal state when any of the single-layer viewing modes is selected. In such a state, the window manager, or other process that provides the functionality of the present invention, receives notification from an event manager of all events such as keyboard navigation, mouse clicks, etc. These events come under its control, and therefore do not interfere with the operation of any of the application programs that are currently executing. Such a state of control also permits the operating system to handle drag-and-drop actions, and other user interface types of activities that are occurring in the computer system. 
     As noted previously, when the “All Windows” mode is selected, the desktop region is dimmed, to thereby highlight the windows being viewed. Similarly, when the “Application Windows” mode is selected, the windows that are not associated with the active application are dimmed, as well as the desktop region. These dimming functions can be achieved by generating a backdrop window that covers the entire boundary area  58 , and has a variable opacity value. This window is inserted at the appropriate level in the series of windows to achieve the desired results. For instance, when the “All Windows” mode is selected, the backdrop window is inserted at the rearmost level, so that it only obscures the view of the desktop objects, but not any of the open windows. The opacity value of this backdrop window might transition from a value of 0% to a value of 60% during the animation in which the windows are being repositioned and resized. 
     For the “Application Windows” mode, the backdrop window is inserted at a level behind the levels of the active application windows, but in front of all other windows. Again, the opacity can transition from 0% to 60%, or any other suitable value, as the application windows are being repositioned. 
     When switching between the “All Windows” mode and the “Application Windows” mode, two backdrop windows are preferably used. For instance, in the “All Windows” mode, the rearmost backdrop window may be displayed with an opacity value of 60%. When the “Applications Window” mode is subsequently selected, a second backdrop window is inserted behind the application windows, with an initial opacity value of 0%. Then, as the transition between the two modes is occurring, a cross-fade can occur between the two backdrop windows. As an example, the rear backdrop window fades out, going from 60% opacity to 0% opacity, while the forward backdrop window fades in from 0% to 60%. The fade-in/fade-out rates of the two windows are coordinated so that, as the non-active application windows are dimmed relative to the active application windows, the dimness of the desktop appears to remain constant. Similarly, when transitioning from the “Application Windows” mode to the “All Windows” mode, the converse operation is carried out, so that the non-active windows re-appear while the desktop remains at a constant level of dimness. 
     Some types of secondary windows may not need to appear on the display during the flattened viewing mode. For example, a tool palette typically would not be selectable in this mode. In such a case, therefore, windows of this type can be removed from the display space while the selectable primary windows are being repositioned and viewed in the flattened mode. 
     In other cases, it might be desirable to have certain types of secondary windows remain on the display. For example, it may be useful to be able to view a drawer that extends from a primary window. In such a case, the drawer should stay with the primary window from which it extends. To accomplish such a result, the primary window and the drawer can be treated as a single composite window, so that they remain together as the repositioning is taking place. 
     In the foregoing example, the windows are repositioned in directions corresponding to vectors that interconnect overlapping windows, to thereby maintain their relative positions to the extent possible. In another implementation, a different rule might be used to determine window placement. For example, the foremost window could be placed in the upper left corner of the border area  58 . The window at the next depth level could be placed immediately to its right, or below it, and so on, such that the windows appear in rows or columns on the display in accordance with their relative levels of depth. For this arrangement, a visible or invisible grid pattern can be established on the display, and the initial movement vector for each window can extend from the location of the window to a designated cell in the grid. As a variant of this approach, the windows could be grouped by application, so that the windows belonging to one application appear in the upper left corner, those for another application appear in the upper right corner, and so forth. 
     As noted previously, the present invention is not limited to the display of windows in a graphical user interface. Rather, it can be applied to any type of object that is capable of being obscured by another object. For instance, it might be used to reposition icons or thumbnail images in a folder, so that the user can locate and select any desired one of them. It can also be applied to a combination of different types of objects, e.g. menus, icons, windows, control strips, etc., so that they can all be simultaneously viewed by the user. 
     Further in this regard, the ability to reposition objects so that they can all be viewed simultaneously is not limited to objects appearing on the computer display. It can also be applied to the printing of images. For example, it can be employed to arrange multiple photographic images that are to be printed on a single page. 
     In summary, therefore, it can be seen that the user interface a the present invention provides an effective mechanism for accessing any one of a number of objects that are simultaneously presented to the user. By repositioning the objects to mutually exclusive areas on the display or page, and resizing them as necessary to do so, the present invention enables the user to readily ascertain the content of every such object. While the objects are in the flattened viewing mode, the user can select any desired one of them. In the case of windows, the selected window becomes the active window when the display is returned to the normal viewing mode. In addition, while all of the objects are simultaneously accessible, the user can perform other types of operations, such as dragging an attachment for an e-mail message from one window to another window that might be otherwise hidden. Similarly, the user can close any windows that may no longer be desired, or minimize any that need not be currently open. 
     It will be appreciated by those of ordinary skill in the art that the present invention can be embodied in other specific forms, without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative, and not restrictive. The scope of the invention is indicated by the appended claims, rather than the foregoing description, and all changes that come within the meaning and range of equivalents thereof are intended to be embraced therein.