Abstract:
A method, apparatus, and computer instructions for displaying data. Each entry in a plurality of entries for an overlay window attribute table (WAT) is set with identical information in which a window identifier is unnecessary for accessing the information in the overlay WAT. Information in a color WAT is retrieved using the set of window identifiers in response to receiving a set of window identifiers. The information in the overlay WAT is retrieved without requiring the window identifier. Pixels are displayed on a display screen using the information retrieved from the color WAT and the information retrieved from the overlay WAT.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Technical Field  
           [0002]    The present invention relates generally to an improved data processing system, and in particular, to a method and apparatus for processing graphics data. Still more particularly, the present invention provides a method and apparatus for displaying pixels without requiring window identifier support for overlay pixels.  
           [0003]    2. Description of Related Art  
           [0004]    Computer graphics concerns the synthesis or display of real or imaginary objects from computer-based models. In computer graphics systems, images are displayed on a display device to a user in two-dimensional and three-dimensional forms. These images are displayed using pixels. A pixel is short for a picture element. One spot in a rectilinear grid of thousands of such spots that are individually “painted” to form an image produced on the screen by a computer or on paper by a printer. A pixel is the smallest element that display or print hardware and software can manipulate in creating letters, numbers, or graphics. These pixels and information relating to these pixels are stored in a buffer. The information describing a pixel is identified using a window ID (WID). A WID is used as an index into a window attribute table (WAT). The WAT contains information describing how a pixel will be displayed on the screen. For example, a WAT identifies depth, colormap, buffer, and gamma for a pixel.  
           [0005]    Typically, the WID is drawn into a separate buffer, which is used to describe how the pixels in the frame buffer or buffers will be displayed. Some graphics systems, such as, for example, UNIX servers, use overlays to enhance the performance of three-dimensional applications, which need to be overlaid on top of a three-dimensional application. An example of such is a menu. These types of servers typically require a separate WID buffer for the color planes and overlays so that multiple pixel interpretations can be supported on a per-pixel basis, which is required for transparent overlay support. A pixel interpretation is the way in which a pixel is displayed. Pixel interpretation involves displaying a pixel based on information or attributes associated or designated for the pixel, such as whether the pixel is 8 bits or 24 bits in depth. This pixel interpretation also includes other attributes, such as, for example, the colormap and the gamma map. Production of graphic cards that provide this support is expensive.  
           [0006]    Therefore, it would be advantageous to have an improved method, apparatus, and computer instructions for providing overlay support without requiring dedicated WID hardware.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention provides a method, apparatus, and computer instructions for displaying data. Each entry in a plurality of entries for an overlay window attribute table (WAT) is set with identical information in which a window identifier is unnecessary for accessing the information in the overlay WAT. Information in a color WAT is retrieved using the set of window identifiers in response to receiving a set of window identifiers. The information in the overlay WAT is retrieved without requiring the window identifier. Pixels are displayed on a display screen using the information retrieved from the color WAT and the information retrieved from the overlay WAT.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:  
         [0009]    [0009]FIG. 1 is a pictorial representation of a data processing system in which the present invention may be implemented in accordance with a preferred embodiment of the present invention;  
         [0010]    [0010]FIG. 2 is a block diagram illustrating a data processing system in which the present invention may be implemented;  
         [0011]    [0011]FIG. 3 is a block diagram illustrating a graphics adapter in accordance with a preferred embodiment of the present invention;  
         [0012]    [0012]FIGS. 4A and 4B are diagrams of window attribute tables in accordance with a preferred embodiment of the present invention;  
         [0013]    [0013]FIG. 5 is a diagram illustrating a window attribute table in accordance with a preferred embodiment of the present invention; and  
         [0014]    [0014]FIG. 6 is a flowchart of a process used for displaying pixels in accordance with a preferred embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0015]    With reference now to the figures and in particular with reference to FIG. 1, a pictorial representation of a data processing system in which the present invention may be implemented is depicted in accordance with a preferred embodiment of the present invention. A computer  100  is depicted which includes a system unit  110 , a video display terminal  102 , a keyboard  104 , storage devices  108 , which may include floppy drives and other types of permanent and removable storage media, and mouse  106 . Additional input devices may be included with personal computer  100 . Computer  100  can be implemented using any suitable computer, such as an IBM eServer computer or IntelliStation computer, which are products of International Business Machines Corporation, located in Armonk, N.Y. Although the depicted representation shows a computer, other embodiments of the present invention may be implemented in other types of data processing systems, such as a network computer. Computer  100  also preferably includes a graphical user interface that may be implemented by means of systems software residing in computer readable media in operation within computer  100 .  
         [0016]    With reference now to FIG. 2, a block diagram illustrating a data processing system is shown in which the present invention may be implemented. Data processing system  200  is an example of a computer, such as computer  100  in FIG. 1, in which code or instructions implementing the processes of the present invention may be located. Data processing system  200  employs a peripheral component interconnect (PCI) local bus architecture. Although the depicted example employs a PCI bus, other bus architectures such as Accelerated Graphics Port (AGP) and Industry Standard Architecture (ISA) may be used. Processor  202  and main memory  204  are connected to PCI local bus  206  through PCI bridge  208 . PCI bridge  208  also may include an integrated memory controller and cache memory for processor  202 . Additional connections to PCI local bus  206  may be made through direct component interconnection or through add-in boards. In the depicted example, local area network (LAN) adapter  210 , small computer system interface SCSI host bus adapter  212 , and expansion bus interface  214  are connected to PCI local bus  206  by direct component connection. In contrast, audio adapter  216 , graphics adapter  218 , and audio/video adapter  219  are connected to PCI local bus  206  by add-in boards inserted into expansion slots. The processes of the present invention may be used to manage rendering of data by graphics adapter  218  or audio/video adapter  219 .  
         [0017]    Expansion bus interface  214  provides a connection for a keyboard and mouse adapter  220 , modem  222 , and additional memory  224 . SCSI host bus adapter  212  provides a connection for hard disk drive  226 , tape drive  228 , and CD-ROM drive  230 . Typical PCI local bus implementations will support three or four PCI expansion slots or add-in connectors.  
         [0018]    An operating system runs on processor  202  and is used to coordinate and provide control of various components within data processing system  200  in FIG. 2. The operating system may be a commercially available operating system such as OS/2, which is available from International Business Machines Corporation. “OS/2” is a trademark of International Business Machines Corporation. An object oriented programming system such as Java may run in conjunction with the operating system and provides calls to the operating system from Java programs or applications executing on data processing system  200 . “Java” is a trademark of Sun Microsystems, Inc. Instructions for the operating system, the object-oriented operating system, and applications or programs are located on storage devices, such as hard disk drive  226 , and may be loaded into main memory  204  for execution by processor  202 .  
         [0019]    Those of ordinary skill in the art will appreciate that the hardware in FIG. 2 may vary depending on the implementation. Other internal hardware or peripheral devices, such as flash read-only memory (ROM), equivalent nonvolatile memory, or optical disk drives and the like, may be used in addition to or in place of the hardware depicted in FIG. 2. Also, the processes of the present invention may be applied to a multiprocessor data processing system.  
         [0020]    For example, data processing system  200 , if optionally configured as a network computer, may not include SCSI host bus adapter  212 , hard disk drive  226 , tape drive  228 , and CD-ROM  230 , as noted by dotted line  232  in FIG. 2 denoting optional inclusion. In that case, the computer, to be properly called a client computer, must include some type of network communication interface, such as LAN adapter  210 , modem  222 , or the like. As another example, data processing system  200  may be a stand-alone system configured to be bootable without relying on some type of network communication interface, whether or not data processing system  200  comprises some type of network communication interface. As a further example, data processing system  200  may be a Personal Digital Assistant (PDA) device which is configured with ROM and/or flash ROM in order to provide nonvolatile memory for storing operating system files and/or user-generated data.  
         [0021]    The depicted example in FIG. 2 and above-described examples are not meant to imply architectural limitations. For example, data processing system  200  also may be a notebook computer or hand held computer in addition to taking the form of a PDA. Data processing system  200  also may be a kiosk or a Web appliance.  
         [0022]    Turning next to FIG. 3, a block diagram illustrating a graphics adapter is depicted in accordance with a preferred embodiment of the present invention. Graphics adapter  300  is an example of a graphics adapter, such as graphics adapter  218  in FIG. 2. Graphics adapter  300  includes an adapter memory  302 , a random access memory digital to analog converter (RAMDAC)  304 , a color WAT table  306 , and an overlay WAT table  308 . Adapter memory  302  includes a color frame buffer  310 , an overlay frame buffer  312 , and a WID buffer  314 . The two frame buffers contain pixels, which are sent to RAMDAC  304  for output to a display device. RAMDAC  304  is a graphics controller chip that maintains the color palette and converts data from memory into analog signals for a display device.  
         [0023]    WID buffer  314  contains WIDs that are used as an index into color WAT table  306  and overlay WAT table  308 . Each of these WAT tables describes how a pixel will be shown on a display device.  
         [0024]    The present invention provides a method, apparatus, and computer instructions for reducing the WIDs needed to display pixels in different frame buffers. Specifically, with currently available systems, one window attribute table is assigned for color frame buffer  310  and a second window attribute table is assigned to overlay frame buffer  312 . Previously, at least one WID would be required for use in displaying overlay information. As a result, in most graphics adapters, N number of WIDs are assigned to the overlay frame buffer and N number of WIDs are assigned to the color frame buffer. Currently, a WID also is required to turn off pixels in overlay frame buffer  312  to allow for pixels in color frame buffer  310  to be displayed. Such a mechanism also reduces the number of WIDs available by 1. As a result, if a single WID is assigned for pixel interpretations in overlay frame buffer  312 , then N −1 WIDs are currently available for different pixel interpretations. A pixel interpretation involves, for example, a different color depth or colormap.  
         [0025]    The present invention provides an improved method, apparatus, and computer instructions for handling window attribute information in a manner that does not require a WID to be associated with overlay information. For example, the information in overlay WAT  308  may be set such that all of the information is identical for each entry. Thus, the particular WID used does not matter with respect to the information obtained from overlay WAT  308 . Thus, all of the WIDS may be assigned for use in color interpretations for color WAT  306 . Different WIDs used for color WAT  306  result in different pixel interpretation information being obtained from color WAT  306 , but always the same information from overlay WAT  308 .  
         [0026]    In another embodiment of the present invention, the mechanism of the present invention employs a single table in which all entries for overlay and transparency fields are enabled and share the same overlay colormap. By combining information in the entries and not requiring a second WAT table, the number of pixel interpretations with the same number of WIDs are increased. In this manner, no need is present for a WID to be designated for the overlay. All of the WIDs may be used in the color planes to display different pixel interpretations.  
         [0027]    Further, the particular WIDs written into WID buffer  314  do not matter when displaying pixels in overlay frame buffer  312 . The transparent field is set in the WAT entry, causing the WID to display the color frame buffer if the particular transparent pixel value is present. For example, this pixel value may be “FF”. Therefore, if this pixel value is present in overlay frame buffer  312 , the WID will cause the color frame buffer pixel in color frame buffer  310  to be displayed. As a result, a WID for turning off the overlay frame buffer is unnecessary. In this manner, N+1 number of pixel interpretations may be provided when N number of WIDs are present.  
         [0028]    With reference now to FIGS. 4A and 4B, diagrams of window attribute tables are depicted in accordance with a preferred embodiment of the present invention. Color window attribute (WAT)  400 , in FIG. 4A, contains information used for pixel interpretations in a color frame buffer, such as color frame buffer  310  in FIG. 3. Color WAT  400  includes WID field  402 , pixel type field  404 , colormap field  406 , buffer field  408 , and gamma field  410 . WID field  402  is used as an index into entries into color WAT  400 . Pixel type field  404  is used to identify the type of pixel, such as 8 bits or 24 bits. Colormap field  406  indicates the particular colormap that is to be used to display the pixel. Buffer field  408  is used in the instance in which a double buffer is present and identifies whether the front or back buffer is to be used. Gamma field  410  is used to identify a gamma map for the pixel.  
         [0029]    In FIG. 4B, overlay WAT  412  includes WID field  414 , colormap field  416 , transparent field  418 , and overlay field  420 . WID field  414  is used as an index into the entries in overlay WAT  412 . Colormap field  416  identifies the particular colormap used for the pixel. Transparent field  418  is used to indicate that the overlay frame buffer may be transparent, allowing a pixel in a color frame buffer to be displayed in place of a corresponding pixel in the overlay frame buffer. A corresponding pixel is a pixel that would be displayed in the same location as a pixel in another frame buffer. Overlay field  420  indicates that the pixel is an overlay pixel type. If this field is set to no, the corresponding pixel in the color buffer is displayed. In these examples, all of the information for colormap field  416 , transparent field  418 , and overlay field  420  are the same for each WID. As a result, all of the WIDS may be assigned for use in different interpretations in color WAT  400 . The same WIDs are used in overlay WAT  412 , rather than different WIDS as currently used. No WID is required to be associated with the overlay information because the same information is returned for any WID that is used as an index into overlay WAT  412 . As a result, all of the WIDs are available for interpretations in the color frame buffer.  
         [0030]    With reference now to FIG. 5, a diagram illustrating a window attribute table is depicted in accordance with a preferred embodiment of the present invention. In this example, table  500  includes WID field  502 , pixel type field  504 , color colormap field  506 , overlay colormap field  508 , transparent field  510 , and overlay field  512  in each of the entries. WID field  502  is used as an index into table  500 . Pixel type field  504  contains information used to identify the particular pixel type, such as 8 bits or 24 bits. Color colormap field  506  includes information used to identify the colormap to be used in a color frame buffer, such as color frame buffer  310  in FIG. 3. Overlay colormap field  508  is used to identify the colormap that is to be used in an overlay frame buffer, such as overlay frame buffer  312  in FIG. 3. Transparent field  510  is used to indicate that the overlay frame buffer may be transparent allowing a pixel in the color frame buffer to be displayed in place of the corresponding pixel in the overlay frame buffer. The mechanism of the present invention allows for this transparency when the feature is enabled in this field by the presence of a selected value in the overlay framebuffer. Any value may be used, but in these examples, the value is “FF”. Overlay field  512  indicates that the pixel is an overlay pixel type.  
         [0031]    Overlay colormap field  508 , transparent field  510 , and overlay field  512  are fields normally found in a separate overlay window attribute table, but are placed into this combined color and overlay window attribute table in a manner in which the particular WID used does not matter because all of the information for each of these fields is identical throughout the table.  
         [0032]    In this example, a buffer and gamma field are not included in table  500 . Depending on the particular implementation, these fields may be included if the hardware supports adding additional fields for the tables. With a combined table, an overlay WAT, such as overlay WAT  308  in FIG. 3, is unnecessary. In fact, the hardware may now be used to support additional types of pixel interpretations for the color frame buffer.  
         [0033]    With reference now to FIG. 6, a flowchart of a process used for displaying pixels is depicted in accordance with a preferred embodiment of the present invention. The process illustrated in FIG. 6 may be implemented in a processing unit, such as one in RAMDAC  304  in FIG. 3. This process uses WATS, such as color WAT  306  and overlay WAT  308  with tables, such as color WAT  400  and overlay WAT  412  illustrated in FIGS. 4A and 4B.  
         [0034]    The process begins by setting the color frame buffer window attribute table (step  600 ). All overlay frame buffer window attribute table entries are set to be the same transparent pixel interpretation (step  602 ). These entries are set such that the information is identical for each entry, such as illustrated for overlay WAT  412  in FIG. 4B. The window ID buffer is examined (step  604 ). This window ID buffer is one such as WID buffer  314  in FIG. 3. This information is used as an index into the WATs.  
         [0035]    Next, a determination is made as to whether the window ID in the overlay WAT is overlay enabled (step  606 ). If the window ID in the overlay is WAT overlay enabled, a determination is made as to whether the window ID in the overlay WAT is transparent (step  608 ). If the window ID in the overlay WAT is transparent, a determination is made as to whether the pixel value in the overlay frame buffer indicates that the pixel is transparent (step  610 ). For example, this value may be “0xFF”. This particular value is selected as one that indicates that the pixel in the overlay frame buffer is transparent such that the pixel in the color frame buffer corresponding to the pixel in the overlay frame buffer is displayed. Such a feature does not require the use of a WID to turn off the pixel in the overlay frame buffer. If the pixel value in the overlay frame buffer is transparent, the pixel is displayed in the color frame buffer (step  612 ) and the process terminates thereafter.  
         [0036]    With reference again to step  610 , if the pixel value in the overlay frame buffer is not transparent, the pixel is displayed in the overlay frame buffer (step  614 ) and the process terminates thereafter. Referring again to step  608 , if the window ID in the overlay WAT is not transparent, the process proceeds to step  614  as described above. Returning again to step  606 , if the window ID in the overlay WAT is not overlay enabled, the process proceeds to step  612  as described above.  
         [0037]    Thus, the present invention provides an improved method, apparatus, and computer instructions for displaying pixels in a data processing system in such a manner that a separate overlay WID is not required. This advantage is achieved by using the same interpretation for overlay pixels in all of the entries as described above. As a result, WIDs that would be used for overlay support may now be used for displaying pixels in the color frame buffer.  
         [0038]    It is important to note that while the present invention has been described in the context of a fully functioning data processing system, those of ordinary skill in the art will appreciate that the processes of the present invention are capable of being distributed in the form of a computer readable medium of instructions and a variety of forms and that the present invention applies equally regardless of the particular type of signal bearing media actually used to carry out the distribution. Examples of computer readable media include recordable-type media, such as a floppy disk, a hard disk drive, a RAM, CD-ROMs, DVD-ROMs, and transmission-type media, such as digital and analog communications links, wired or wireless communications links using transmission forms, such as, for example, radio frequency and light wave transmissions. The computer readable media may take the form of coded formats that are decoded for actual use in a particular data processing system.  
         [0039]    The description of the present invention has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiment was chosen and described in order to best explain the principles of the invention, the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.