Overlay graphics memory management method and apparatus

• US 6,396,473 B1
• Filed: 04/22/1999
• Issued: 05/28/2002
• Est. Priority Date: 04/22/1999
• Status: Expired due to Fees

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: WebTV Networks Inc. (Microsoft Corporation)
• Inventors: Anderson, David R., Callahan, Sean M.
• Primary Examiner(s): Shalwala, Bipin
• Assistant Examiner(s): Frenel, Vanel
• Application Number:
  US09/299,454
• Time in Patent Office: 1,132 Days
• Field of Search: 345/113-116,435,536,543,531,561,548
• US Class Current: 345/530
• CPC Class Codes: G09G 2320/103 Detection of image changes, e.g. determination of an index representative of the image change
• CPC Class Codes: G09G 2340/10 Mixing of images, i.e. displayed pixel being the result of an operation, e.g. adding, on the corresponding input pixels
• CPC Class Codes: G09G 2360/122 Tiling
• 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: H04N 21/42653 for processing graphics
• CPC Class Codes: H04N 21/4435 Memory management allocation of memory to service a request G06F9/5016; addressing or allocating within memory systems or architectures G06F12/02
• CPC Class Codes: H04N 5/44504 Circuit details of the additional information generator, e.g. details of the character or graphics signal generator, overlay mixing circuits

Abstract

The invention frees up memory to other uses by allocating memory to video graphics buffering only to the extent required. It also saves graphic processor bandwidth by processing, e.g. blending, only to the extent required. It does so by defining a regular grid of so-called tiles or cells in the overlay graphic data window, e.g orthogonally arrayed squares of 32-pixel sides, and allocating memory only to those requiring update, i.e. only those that are visible and subject to change between successive frames. Allocation is dynamic and requires little tagging overhead to keep track of the tiles in memory by location in the video graphic window. Processing is only of those tiles for which memory is allocated, since entirely transparent tiles within the window require no blending or processing whatsoever because they are invisible. In one implementation, only onscreen buffered graphics are tiled and the offscreen buffered graphics require full-sized memory allocation and in another offscreen buffered graphics are tiled also by clipping within variously sized buffers during successive passes through a drawing operation wherein the various sized buffers all are smaller than the entire window. New offscreen buffer-processed tiles may be swapped as they are processed for existing (visible) onscreen tiles directly, when there is less available memory, or new tiles may be processed and block-stored in memory until a wholesale swap can occur invisibly, when there is more memory available.

Claims

1. In a system comprised of a display monitor and a graphic processor for processing an overlay window image and a background image for simultaneous display on the monitor, and wherein the system comprises a background buffer for storing data corresponding to the background image and an overlay buffer for storing data corresponding to the overlay window image, a method for reducing the amount of data that must be processed when the overlay window image is updated, the method comprising:

defining a plurality of overlay;

window cells which correspond to the overlay window;

determining which overlay window cells are visible and thus subject to change over a given period of time, and which are transparent and thus not subject to change over the same period of time;

identifying which of one or more visible overlay window cells has actually changed over the given period of time;

allocating within an update buffer, one or more update buffer cells corresponding to each of one or more visible overlay window cells that has been identified as changing over the given period of time; and

processing data to create a blended image that includes both the background image and the overlay image as it changes, by blending (i) only that data from the one or more update buffer cells that have been allocated for each of the one or more visible overlay window cells identified as changing, with (ii) data for the background image that corresponds to the location of the one or more visible overlay window cells identified as changing.

2. The method of claim 1, wherein said blending includes weighting the overlay image data with the background image data in a defined ratio to produce a transparent overlay of such overlay image data on the background image for said displaying.

3. The method of claim 1, wherein said allocating is dynamically responsive to the spatial extent of change of overlay image data between successive time periods, said allocating being characterized in that when the extent of change is relatively high, a larger amount of memory is allocated to the update buffer and when the extent of change is relatively low, a smaller amount of memory is allocated to the update buffer.

4. The method of claim 1, wherein said identifying and said allocating are characterized such that a two-dimensional orthogonal array of pixel-containing cells is produced in the update buffer, the orthogonal array containing cells of a number and location determined at lent in part by a spatial extent of change of overlay image data between successive time periods.

5. The method of claim 4 in which the update buffer contains a given number of pixels, wherein said identifying and said allocating are performed in such manner that the produced cells are of predefined size and shape containing a predefined number of the pixels within the update buffer.

6. The method of claim 1, wherein each of the allocated one or more update buffer cells is an onscreen update buffer cell, and wherein changes to the corresponding overlay window cell are made directly to the one or more onscreen update buffer cells.

7. The method of claim 1, wherein each of the allocated one or more update buffer cells is a new offscreen update buffer cell, and wherein changes to the corresponding overlay window cell are made directly to the one or more new offscreen update buffer cells.

8. The method of claim 1, wherein the update buffer includes at least one existing onscreen update buffer cell that has been allocated prior to the one or more new offscreen update buffer cells, the method further comprising:

swapping the one or more new offscreen update buffer cells with the at least one existing onscreen update buffer cell, such that one or more new offscreen update buffer cells become one or more onscreen update buffer cells, and such that the at least one existing onscreen update buffer cell is no longer used; and

deallocating the at least one existing onscreen update buffer cell after it is no longer used.

9. The method of claim 8, wherein only a portion of the one or more update buffer cells corresponding to each of the one or more visible overlay windows cells that has been identified as changing over the given period of time are allocated initially, and wherein the method further comprises iteratively allocating, swapping, and deallocating, until all of the one or more update buffer cells have been allocated.

10. The method of claim 1, wherein the overlay buffer stores only a portion of the data corresponding to the overlay window image at any given time.

11. The method of claim 1, wherein none of doe one of more visible overlay window cells is identified as actually changing over the given period of time.

12. In a system comprised of a display monitor and a graphic processor for processing an overlay window image and a background image for simultaneous display on the monitor, and wherein the system comprises a background buffer for storing data corresponding to the background image and an overlay buffer for storing data corresponding to the overlay window image, a method for reducing the amount of data that must be processed when the overlay window image is updated, the method comprising:

defining a plurality of overlay window cells which correspond to the overlay window;

identifying which of one or more overlay window cells has actually changed over a given period of time;

allocating within an update buffer, one or more update buffer cells corresponding to each of one or more overlay window cells that has been identified as changing over the given period of time, wherein each of the allocated one or more update buffer cells is either an onscreen update buffer cell or a new offscreen update buffer cell, and wherein changes to the corresponding overlay window cell are made directly to the one or more update buffer cells; and

processing data to create a blended image that includes both the background image and the overlay image as it changes, by blending (i) only tat data from the one or more update buffer cells that have been allocated for each of the one or more overlay window cells identified as changing, with (ii) data for the background image that corresponds to the location of the one or more overlay window cells identified as changing.

13. The method of claim 12, wherein the update buffer comprises at least one existing onscreen update buffer cell that has been allocated prior to one or more new offscreen update buffer cells, the method further comprising:

swapping the one or more new offscreen update buffer cells with the at least one existing onscreen update buffer cell, such that one or more new offscreen update buffer cells become one or more onscreen update buffer cells, and such that the at least one existing onscreen update buffer cell is no longer used; and

deallocating the at least one existing onscreen update buffer cell after it is no longer used.

14. The method of claim 13, wherein only a portion of the one or more update buffer cells corresponding to each of the one or more overlay windows cells that has been identified as changing over the given period of time are allocated initially, and wherein the method further comprises iteratively allocating, swapping, and deallocating, until all of the one or more update buffer cells have been allocated.

15. The method of claim 12, further comprising determining which overlay window cells are visible and thus subject to change over a given period of time, and which are transparent and thus not subject to change over the same period of time.

16. The method of claim 12, wherein the overlay buffer stores only a portion of the data corresponding to the overlay window image at any given time.

17. A graphics system for using a display monitor to display a blended image comprised of a background image and an overlay window image, comprising:

a graphic processor for processing the overlay window image and the background image for simultaneous display on the display monitor;

a background buffer for storing data corresponding to the background image, and for communicating data to the graphic processor;

an overlay buffer for storing data corresponding to the overlay window image, and for communicating data to the graphic processor; and

buffer control means for controlling the amount of data that must be processed when the overlay window image is updated, said buffer control means comprising;

means for defining a plurality of overlay window cells which correspond to the overlay window;

means for determining which overlay window cells are visible and thus subject to change over a given period of time, and which are transparent and thus not subject to change over the same period of time;

means for identifying which of one or more visible overlay window cells has actually changed over the given period of time;

means for allocating within an update buffer, one or more update buffer cells corresponding to each of one or more visible overlay window cells that has been identified as changing over the given period of time; and

means for communicating data as determined by the buffer control means to the graphic processor, the graphic processor thereafter processing the received data to create a blended image that includes both the background image and the overlay image as it changes, by blending (i) only that data from the one or more update buffer cells that have been allocated for each of the one or more visible overlay window cells identified as changing, with (ii) data for the background image that corresponds to the location of the one or more visible overlay window cells identified as changing.

18. The graphics system of claim 17, wherein the graphic processor comprises means for weighting the overlay image data with the background image data in a defined ratio to produce a transparent overlay of the overlay image data on the background image for displaying.

19. The graphics system of claim 17, wherein the allocating means is dynamically responsive to the spatial extent of change of overlay image data between successive time periods, the allocating means being characterized in that when the extent of change is relatively high, a larger amount of memory is allocated to the update buffer and when the extent of change is relatively low, a smaller amount of memory is allocated to the update buffer.

20. The method of claim 17, wherein the means for identifying and the means for allocating are characterized such that a two-dimensional orthogonal array of pixel-containing cells is produced in the update buffer, the orthogonal array containing cells of a number and location determined at least in part by a spatial extent of change of overlay image data between successive time periods.

21. The graphics system of claim 17, wherein each of the allocated one or more update buffer cells is an onscreen update buffer cell, the graphics system further comprising means for directly changing the one or more onscreen update buffer cells based on changes to the corresponding overlay window cell.

22. The graphics system of claim 17, wherein each of the allocated one or more update buffer cells is a new offscreen update buffer cell, the graphics system further comprising means for directly changing the one or more offscreen update buffer cells based on changes to the corresponding overlay window cell.

23. The graphics system of claim 22, wherein the update buffer includes at least one existing onscreen update buffer cell that has been allocated prior to the one or more new offscreen update buffer cells, the graphics system further comprising:

means for swapping the one or more new offscreen update buffer cells with the at least one existing onscreen update buffer cell, such that one or more new onscreen update buffer cells become one or more onscreen update buffer cells, and such that the at least one existing onscreen update buffer cell is no longer used; and

means for deallocating the at least one existing onscreen update buffer cell after it is no longer used.

24. The graphics system of claim 23, wherein only a portion of the one or more update buffer cells corresponding to each of the one or more visible overlay windows cells that has been identified as changing over the given period of time are allocated initially, and wherein the graphics system further comprises means for iteratively allocating, swapping, and deallocating, until all of the one or more update buffer cells have been allocated.

25. The graphics system of claim 17, wherein the overlay buffer is sized so as to store only a portion of the overlay window image at any given time.

26. The graphics system of claim 17, wherein the means for identifying does not identify any of the one or more visible overlay window cells as actually changing over the given period of time.