Emulating screen overlays by flip-mapping memory

• US 6,326,969 B1
• Filed: 05/18/1998
• Issued: 12/04/2001
• Est. Priority Date: 12/20/1996
• Status: Expired due to Term

• Current Assignee: Comcast Cable Communications Management LLC (Comcast Corporation)
• Original Assignee: Liberate Technologies
• Inventors: Helman, Jim, Vickers, Mark A.
• Primary Examiner(s): Vo., Cliff N.
• Application Number:
  US09/080,575
• Time in Patent Office: 1,296 Days
• Field of Search: 345/435, 345/436, 345/113, 345/114, 345/434
• US Class Current: 345/629
• CPC Class Codes: G06F 16/9535 Search customisation based on user profiles and personalisation
• CPC Class Codes: G09G 5/397 Arrangements specially adapted for transferring the contents of two or more bit-mapped memories to the screen simultaneously, e.g. for mixing or overlay G09G5/02 takes precedence
• CPC Class Codes: Y10S 707/99935 Query augmenting and refining, e.g. inexact access

Abstract

A method and apparatus for managing background and foreground display images. Graphics memory for images which are rendered in software is referenced by a processor using an MMU (memory mapping unit) having MMU tables. The graphics memory includes a portion for on-screen display, and a portion which can be written into but which is not displayed. When a background image is overlaid by a foreground image, the portion of the background image overlaid is copied to a save-away area, and the MMU tables are altered so that software rendering of the background image automatically occurs in the save-away area. However, the foreground image is written directly into the on-screen display area by rendering hardware. This allows the software-rendered image to be kept up to date, and allows data for the software-rendered image not to be lost during the time the background image is covered up. When the background image is no longer overlaid by the foreground image, the portion of the background image which was overlaid is copied back from the save-away area to the on-screen display area. The MMU tables are altered so that software rendering of the background image thereafter automatically occurs in the on-screen display area This allows the software-rendered image to be quickly displayed on screen in its updated form.

Claims

1. A method of managing background and foreground images in a graphics display system, the method comprising the steps of:

copying image data corresponding to at least a portion of a background image which is intended to be covered by at least a portion of a foreground image from an on-screen memory portion to a save-under area;

covering said at least a portion of said background image with at least a portion of said foreground image;

routing modified image data to said save-under area when said modified image data corresponds to said portion of said background image covered by said portion of said foreground image; and

routing said modified image data to said on-screen memory portion when said modified image data corresponds to a portion of said background image not covered by any portion of said foreground image.

2. The method in claim 1, further comprising the steps of removing said portion of said foreground image covering said portion of said background image by copying image data corresponding to said background image in said save-under area to said on-screen memory portion.

3. The method in claim 1, wherein said steps of routing include using an MMU having an MMU table to route said modified image data.

4. The method in claim 1, wherein said step of copying and said step of covering said at least a portion of said background image with said at least a portion of said foreground occur substantially simultaneously.

5. The method in claim 1, further including the step of rendering said background image and said foreground image on a display screen.

6. The method of claim 5, wherein said background image is rendered by a computer system operating under program control and said foreground image is rendered by a graphics display system under hardware control.

7. The method in claim 5, wherein said step of rendering said background image and said foreground image is performed by a computer system operating under program control, said computer system using software references to perform said steps of routing said modified image data to said save-under area and to said on-screen memory portion.

23. A method as in claim 1, wherein said routing steps are performed by an MMU so as to allow an application program to generate said modified image data for said background image without regard to what portion of said background image is intended to be covered.

24. A method as in claim 1, wherein said background image is generated under control by an application program, and said foreground image is rendered by a graphics controller independent of control by said application program.

8. A method of managing background and foreground images in a graphics display system, the graphics display system having a memory that includes an on-screen memory portion and an off-screen memory portion, the memory storing the background and foreground images and the graphics display system using the on-screen memory portion as a source of images for display, comprising the steps of:

copying a portion of a background image to be overlaid by a foreground image from the on-screen memory portion to a save-under area within the off-screen memory portion;

routing software references using an MMU which correspond to said portion of the background image to be overlaid to said save-under area, said step of routing enabling said portion of the background image to be overlaid in said save-under area to be written to when said background image is rendered;

rendering the background image to the on-screen memory portion and to the save-under area in response to said software references; and

rendering the foreground image to the on-screen memory portion.

9. The method in claim 8, further comprising the steps of:

removing the foreground image by copying contents of said save-under area to the on-screen memory portion; and

routing said software references to the on-screen memory portion.

10. The method in claim 8, wherein said step of routing includes updating an MMU table.

11. The method in claim 8, wherein said step of rendering the background image and said step of rendering the foreground image occur substantially simultaneously.

12. The method in claim 8, wherein said step of routing includes determining when said portion of the background image to be overlaid is being rendered and altering the software references to refer to the save-under area instead of the on-screen memory portion.

13. The method in claim 8, wherein said step of rendering the background image is performed by a computer system operating under program control and wherein said step of rendering the foreground image is performed by the graphics display system using hardware control.

14. The method in claim 8, wherein said step of rendering the background image and said step of rendering the foreground image are performed by a computer system operating under program control, said computer system using software references to perform said steps of rendering.

25. A method as in claim 8, wherein said routing is performed by said MMU so as to allow an application program to generate said background image without regard to what portion of said background image is intended to be overlaid.

26. A method as in claim 8, wherein said background image is generated under control by an application program, and said foreground image is rendered by a graphics controller independent of control by said application program.

15. An apparatus having a program recorded in a computer-readable medium for laying out a page, the apparatus comprising:

means for copying a portion of a background image to be overlaid by a foreground image for the on-screen memory portion to a save-under area within the off-screen memory portion;

means for routing software references using an MMU which correspond to said overlaid portion of the on-screen memory to said save-under area, said step of routing enabling said overlaid portion in said save-under area to be written to when said background image is rendered;

means for rendering the background image to the on-screen memory portion and to the save-under area in response to said software references in said step of routing; and

means for rendering the foreground image defined within said on-screen memory portion onto said overlaid portion.

16. A computer system for managing background and foreground images in a graphics display system, the system comprising:

an on-screen memory portion;

a save-under area; and

an image data router responsive to software references corresponding to image data, said image data router sending said image data to said save-under area when said image data corresponds to at least a portion of a background image that is overlaid by at least a portion of a foreground image.

17. The computer system in claim 16, further comprising a graphics adapter for rendering foreground images.

18. The computer system in claim 17, further comprising a processor running under software control, said processor rendering images onto a display screen in response to image data saved in said on-screen memory portion.

19. The computer system in claim 16, wherein said image data router is an MMU having an MMJ table for holding software references.

20. The computer system in claim 19, further comprising a graphics adapter for rendering foreground images.

21. The computer system in claim 20, further comprising a processor running under software control, said processor for sending said image data to said MMU and to said graphics adapter, said graphics adapter responsive to said image data corresponding to said at least a portion of said foreground image.

22. The computer system in claim 16, further comprising a processor running under software control, said processor for establishing said software references in response to whether or not said at least a portion of said background image is covered by said at least a portion of said foreground image.

27. An apparatus as in claim 16, wherein said image data router is an MMU that sends said image data to said save under area so as to allow an application program to generate said image data for said background image without regard to what portion of said background image is overlaid.

28. An apparatus as in claim 16, wherein said background image is generated under control by an application program, and said foreground image is rendered by a graphics controller independent of control by said application program.

29. An apparatus having a program recorded in a computer-readable medium for laying out a page, the apparatus comprising:

means for copying a portion of a background image to be overlaid by a foreground image from the on-screen memory portion to a save-under area within the off-screen memory portion;

means for routing software references using an MMU which correspond to said portion of the background image to be overlaid to said save-under area, said means for routing enabling said portion of the background image to be overlaid in said save-under area to be written to when said background image is rendered;

means for rendering the background image to the on-screen memory portion and to the save-under area in response to said software references; and

means for rendering the foreground image to the on-screen memory portion.