Varying effective resolution by screen location by changing active color sample count within multiple render targets

1. A method for graphics processing with a graphics processing system having a graphics processing unit coupled to a display device, comprising: receiving metadata specifying an active sample configuration for a particular region of a screen of the display device among a plurality of regions of the screen; receiving pixel data for one or more pixels of an image in the particular region, wherein the pixel data specifies the same number of color samples for each pixel; and for each pixel in the particular region that is covered by a primitive, invoking a pixel shader only for color samples for the pixel specified to be active samples by the active sample configuration, wherein invoking the pixel shader includes unrolling pixel shader invocations by default, wherein pixel shading computations of the pixel shader super-sample each pixel by virtue of being invoked for each active color sample of each pixel in the particular region that is covered by the primitive, wherein the metadata specifies different active sample configurations for regions of the screen that have different resolutions.

2. The method of claim 1 , wherein the metadata specifies a mask of active samples for the particular region and wherein invoking the pixel shader only for active samples includes performing a logical AND between the mask and a set of samples covered by a primitive to determine the active samples for the primitive for which the pixel shader is to be invoked.

3. The method of claim 1 , wherein the metadata specifies an active sample count for the particular region of the plurality of regions; wherein the active sample count is less than or equal to the number of color samples, wherein the number of color samples is two or more;

wherein invoking the pixel shader only for active samples includes for each pixel in the particular region, invoking a pixel shader only for a number of the color samples for the pixel equal to the active sample count.

4. The method of claim 1 , wherein the metadata is configured such that an active sample count for one or more regions of the plurality located near a center of the screen is greater than an active sample count for one or more regions of the plurality located near a periphery of the screen.

5. The method of claim 1 , wherein the metadata is configured such that an active sample count for one or more regions of the plurality located near a center of the screen is greater than an active sample count for one or more regions of the plurality located near an edge of the screen and wherein the active count for the one or more regions located near the edge of the screen is greater than an active count for one or more regions of the plurality located near a corner of the screen.

6. The method of claim 1 , wherein the display device is characterized by a field of view of 90 degrees or more.

7. The method of claim 1 , wherein the display device is a head-mounted display device.

8. The method of claim 1 , further comprising determining a portion of a screen of the display device that a user is looking at and wherein the metadata is configured to vary the pixel resolution such that pixel resolution is highest for one or more subsections of the screen containing the portion the user is looking at.

9. The method of claim 1 , wherein the metadata is static for given optics and a given field of view of the display device.

10. The method of claim 1 , wherein the metadata is configured to specify different active color samples for different regions of the screen.

11. The method of claim 1 , wherein, each region of the plurality corresponds to a fixed size portion of the screen.

12. The method of claim 1 , wherein each region of the plurality corresponds to a variable size portion of the screen.

13. The method of claim 1 , wherein the metadata defines each region of the plurality of regions by ranges of pixels in vertical and horizontal directions.

14. The method of claim 1 , wherein the metadata defines each region of the plurality by coarse rasterization tiles of some size.

15. The method of claim 1 , wherein a portion of the metadata associated with a particular region of the plurality includes information specifying an active color sample count for the particular region.

16. The method of claim 1 , wherein the metadata is stored in the form of a table in a memory and/or graphics memory.

17. A system for graphics processing, comprising

a graphics processing unit (GPU) configured to

receive metadata specifying an active sample configuration for a particular region of a screen of a display device among a plurality of regions of the screen;

receive pixel data for one or more pixels of an image in the particular region, wherein the pixel data specifies the same number of color samples for each pixel; and

for each pixel in the particular region that is covered by a primitive, invoke a pixel shader only for color samples for the pixel specified to be active samples by the active sample configuration, wherein invoking the pixel shader includes unrolling pixel shader invocations by default, wherein pixel shading computations of the pixel shader super-sample each pixel by virtue of being invoked for each active color sample of each pixel in the particular region that is covered by the primitive, and wherein the metadata specifies different active sample configurations for regions of the screen that have different resolutions.

18. The system of claim 17 , wherein the metadata specifies a mask of active samples for the particular region and wherein the graphics processing unit is configured to invoke the pixel shader only for active samples by performing a logical AND between the mask and a set of samples covered by a primitive to determine the active samples for the primitive for which the pixel shader is to be invoked.

19. The system of claim 17 , wherein the metadata specifies an active sample count for the particular region of the plurality of regions, wherein the active sample count is less than or equal to the number of color samples, wherein the number of color samples is two or more; and

wherein the GPU is configured to invoke the pixel shader only for active samples includes for each pixel in the particular region by invoking a pixel shader only for a number of the color samples for the pixel equal to the active sample count.

20. The system of claim 17 , wherein the metadata is configured such that an active sample count for one or more regions of the plurality located near a center of the screen is greater than an active sample count for one or more regions of the plurality located near a periphery of the screen.

21. The system of claim 17 , wherein the metadata is configured such that an active sample count for one or more regions of the plurality located near a center of the screen is greater than an active sample count for one or more regions of the plurality located near an edge of the screen and wherein the active count for the one or more regions located near the edge of the screen is greater than an active count for one or more regions of the plurality located near a corner of the screen.

22. The system of claim 17 , further comprising the display device, wherein the display device is characterized by a field of view of 90 degrees or more.

23. The system of claim 17 , further comprising the display device, wherein the display device is a head-mounted display device.

24. The system of claim 17 , wherein the system is configured to determine a portion of a screen of the display device that a user is looking at and wherein the metadata is configured to vary the pixel resolution such that pixel resolution is highest for one or more subsections of the screen containing the portion the user is looking at.

25. The system of claim 17 , wherein the system is configured to use static metadata for given optics and field of view of the display device.

26. The system of claim 17 , wherein the metadata is configured to specify different active color samples for different regions of the screen.

27. The system of claim 17 , wherein, each region of the plurality corresponds to a fixed size portion of the screen.

28. The system of claim 17 , wherein each region of the plurality corresponds to a variable size portion of the screen.

29. The system of claim 17 , wherein the metadata defines each region of the plurality of regions by ranges of pixels in vertical and horizontal directions.

30. The system of claim 17 , wherein the metadata defines each region of the plurality by coarse rasterization tiles of some size.

31. The system of claim 17 , wherein a portion of the metadata associated with a particular region of the plurality includes information specifying an active color sample count for the particular region.

32. The system of claim 17 , further comprising a memory and/or graphics memory, wherein the metadata is stored in the form of a table in the memory and/or graphics memory.

33. A non-transitory computer-readable medium having computer executable instructions embodied therein that, when executed, implement a method for graphics processing with a graphics processing system having a graphics processing unit coupled to a display device, the method comprising:

receiving metadata specifying an active sample configuration for a particular region of a screen of the display device among a plurality of regions of the screen;

receiving pixel data for one or more pixels of an image in the particular region, wherein the pixel data specifies the same number of color samples for each pixel; and

for each pixel in the particular region that is covered by a primitive, invoking a pixel shader only for color samples for the pixel specified to be active samples by the active sample configuration, wherein invoking the pixel shader includes unrolling pixel shader invocations by default, wherein pixel shading computations of the pixel shader super-sample each pixel by virtue of being invoked for each active color sample of each pixel in the particular region that is covered by the primitive, and wherein the metadata specifies different active sample configurations for regions of the screen that have different resolutions.