System and method for path rendering with multiple stencil samples per color sample

• US 8,704,830 B2
• Filed: 05/19/2011
• Issued: 04/22/2014
• Est. Priority Date: 05/21/2010
• Status: Active Grant

• Current Assignee: NVIDIA Corporation
• Original Assignee: NVIDIA Corporation
• Inventors: Kilgard, Mark J., Brown, Patrick R.
• Primary Examiner(s): Caschera, Antonio A
• Application Number:
  US13/111,897
• Publication Number:
  US 20110285742A1
• Time in Patent Office: 1,069 Days
• Field of Search: None
• US Class Current: 345/422
• CPC Class Codes: G06T 11/203 Drawing of straight lines or curves
• CPC Class Codes: G06T 15/005 General purpose rendering architectures

Abstract

One embodiment of the present invention sets forth a technique for improving path rendering on computer systems by efficiently representing and computing sub-pixel coverage for path objects. A stencil buffer is configured to store multiple stencil samples per pixel stored in an image buffer. The stencil samples undergo stencil testing to produce a set of Boolean values per pixel, which collectively define a geometric coverage percentage for the pixel. The coverage percentage is used to modulate a color value for the pixel. The modulated color value is then blended into the image buffer as an anti-aliased pixel. This technique advantageously enables efficient anti-aliasing for path rendering.

Claims

1. A method for rendering an image sample associated with a geometric primitive, the method comprising:

selecting the image sample for rendering based on the image sample being at least partially covered by the geometric primitive;

performing a stencil test on each stencil sample covered by the geometric primitive included in a plurality of stencil samples associated with the image sample to generate a set of stencil test results, wherein each stencil test result comprises a Boolean value of either pass or fail;

based on the set of stencil test results, calculating a coverage percentage that indicates how much of the image sample is covered by the geometric primitive object;

computing, via a processing unit, a color value based on a color shading operation associated with the geometric primitive; and

computing a modulated color value for the image sample based on the color value and the coverage percentage.

2. The method of claim 1 wherein the geometric primitive contributes to at least one attribute of a set of attributes that includes coverage, stenciling, and covering for the image sample, as a result of filling or stroking a related path object.

3. The method of claim 1, further comprising blending the modulated color value with a previously stored color value to produce a blended color value.

4. The method of claim 3, wherein blending comprises adding the modulated color value to the product of the difference of one minus an alpha component of the modulated color value and the previously stored color value.

5. The method of claim 1, wherein the coverage percentage comprises the quotient of a count of Boolean pass values divided by a count of stencil samples in the set of stencil samples.

6. The method of claim 1, wherein the plurality of stencil samples comprises four stencil samples, and each stencil sample comprises an eight bit value.

7. The method of claim 1, wherein at least a portion of a storage resource allocated to stencil storage overlaps with a storage resource configured to store depth information.

8. The method of claim 1, wherein a first programmable shader is configured to perform the step of performing a stencil test, and wherein the first programmable shader generates a mask indicating which stencil samples included in the plurality of stencil samples are covered stencil samples.

9. The method of claim 1, wherein a second programmable shader is configured to mark a covered stencil sample for discard prior to the covered stencil sample being subjected to a stencil test.

10. The method of claim 1, wherein computing the modulated color value comprises multiplying the coverage percentage by an alpha color component of the color value.

11. The method of claim 1, wherein computing the modulated color value comprises multiplying the coverage percentage by at least red, green, and blue color components of the color value.

12. A non-transitory computer-readable storage medium including instructions that, when executed by a processing unit, cause the processing unit to render an image associated with a path object, by performing the steps of:

selecting the image sample for rendering based on the image sample being at least partially covered by the geometric primitive;

performing a stencil test on each stencil sample covered by the geometric primitive included in a plurality of stencil samples associated with the image sample to generate a set of stencil test results, wherein each stencil test result comprises a Boolean value of either pass or fail;

based on the set of stencil test results, calculating a coverage percentage that indicates how much of the image sample is covered by the geometric primitive object;

computing a color value based on a color shading operation associated with the geometric primitive; and

computing a modulated color value for the image sample based on the color value and the coverage percentage.

13. The non-transitory computer-readable storage medium of claim 12 wherein the geometric primitive contributes to at least one attribute of a set of attributes that includes coverage, stenciling, and covering for the image sample, as a result of filling or stroking a related path object.

14. The non-transitory computer-readable storage medium of claim 12, further comprising blending the modulated color value with a previously stored color value to produce a blended color value.

15. The non-transitory computer-readable storage medium of claim 14, wherein blending comprises adding the modulated color value to the product of the difference of one minus an alpha component of the modulated color value and the previously stored color value.

16. The non-transitory computer-readable storage medium of claim 12, wherein the coverage percentage comprises the quotient of a count of Boolean pass values divided by a count of stencil samples in the set of stencil samples.

17. The non-transitory computer-readable storage medium of claim 12, wherein the plurality of stencil samples comprises four stencil samples, and each stencil sample comprises an eight bit value.

18. The non-transitory computer-readable storage medium of claim 12, wherein at least a portion of a storage resource allocated to stencil storage overlaps with a storage resource configured to store depth information.

19. The non-transitory computer-readable storage medium of claim 12, wherein a first programmable shader is configured to perform the step of performing a stencil test, and wherein the first programmable shader generates a mask indicating which stencil samples included in the plurality of stencil samples are covered stencil samples.

20. The non-transitory computer-readable storage medium of claim 12, wherein a second programmable shader is configured to mark a covered stencil sample for discard prior to the covered stencil sample being subjected to a stencil test.

21. The non-transitory computer-readable storage medium of claim 12, wherein computing the modulated color value comprises multiplying the coverage percentage by an alpha color component of the color value.

22. The non-transitory computer-readable storage medium of claim 12, wherein computing the modulated color value comprises multiplying the coverage percentage by at least red, green, and blue color components of the color value.

23. A computing device, comprising:

a memory system;

a processing unit coupled to the memory system and configured to;

select a image sample for rendering based on the image sample being at least partially covered by a geometric primitive;

perform a stencil test on each stencil sample covered by the geometric primitive included in a plurality of stencil samples associated with the image sample to generate a set of stencil test results, wherein each stencil test result comprises a Boolean value of either pass or fail;

based on the set of stencil test results, calculating a coverage percentage that indicates how much of the image sample is covered by the geometric primitive;

compute a color value based on a color shading operation associated with the geometric primitive;

compute a modulated color value for the image sample based on the color value and the coverage percentage; and

blend the modulated color value with a previously stored color value and storing a resulting blended color value into the image buffer,

wherein the stencil samples are stored in a stencil buffer, and wherein the stencil buffer and the image buffer reside in the memory system.

24. The computing device of claim 23, wherein the coverage percentage comprises the quotient of a count of Boolean pass values divided by a count of stencil samples in the set of stencil samples, and wherein the processing unit is configured to compute the modulated color value by multiplying the coverage percentage by at least red, green, and blue color components of the color value.