Alpha-to-coverage value determination using virtual samples
First Claim
1. A method of producing a pixel coverage mask based on an alpha value, the method comprising:
- enabling bits in a quantized alpha mask based on an alpha-to-coverage ordering associated with a sampling mode;
combining a virtual coverage mask that indicates which virtual samples and real samples within a pixel are covered by a graphics primitive and a quantized alpha mask based on the alpha value to produce the pixel coverage mask;
determining a link field that indicates links between the virtual samples and the real samples;
adjusting the link field based on the pixel coverage mask to link any orphaned virtual sample to one of the real samples, wherein each virtual sample inherits color data computed for the real sample to which the virtual sample is linked; and
outputting the pixel coverage mask and the link field for the pixel.
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Abstract
One embodiment of the present invention sets forth a technique for converting alpha values into pixel coverage masks. Geometric coverage is sampled at a number of “real” sample positions within each pixel. Color and depth values are computed for each of these real samples. Fragment alpha values are used to determine an alpha coverage mask for the real samples and additional “virtual” samples, in which the number of bits set in the mask bits is proportional to the alpha value. An alpha-to-coverage mode uses the virtual samples to increase the number of transparency levels for each pixel compared with using only real samples. The alpha-to-coverage mode may be used in conjunction with virtual coverage anti-aliasing to provide higher-quality transparency for rendering anti-aliased images.
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Citations
20 Claims
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1. A method of producing a pixel coverage mask based on an alpha value, the method comprising:
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enabling bits in a quantized alpha mask based on an alpha-to-coverage ordering associated with a sampling mode; combining a virtual coverage mask that indicates which virtual samples and real samples within a pixel are covered by a graphics primitive and a quantized alpha mask based on the alpha value to produce the pixel coverage mask; determining a link field that indicates links between the virtual samples and the real samples; adjusting the link field based on the pixel coverage mask to link any orphaned virtual sample to one of the real samples, wherein each virtual sample inherits color data computed for the real sample to which the virtual sample is linked; and outputting the pixel coverage mask and the link field for the pixel. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A non-transitory computer-readable storage medium storing instructions that, when executed by a processor, cause the processor to produce a pixel coverage mask based on an alpha value, by performing the steps of:
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enabling bits in a quantized alpha mask based on an alpha-to-coverage ordering associated with a sampling mode; combining a virtual coverage mask that indicates which virtual samples and real samples within a pixel are covered by a graphics primitive and a quantized alpha mask based on the alpha value to produce the pixel coverage mask; determining a link field that indicates links between the virtual samples and the real samples; adjusting the link field based on the pixel coverage mask to link any orphaned virtual sample to one of the real samples, wherein each virtual sample inherits color data computed for the real sample to which the virtual sample is linked; and outputting the pixel coverage mask and the link field for the pixel.
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11. A system for producing a pixel coverage mask based on an alpha value, the system comprising:
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a processor including an alpha-to-coverage unit that is configured to; enable bits in a quantized alpha mask based on an alpha-to-coverage ordering associated with a sampling mode; combine a virtual coverage mask that indicates which virtual samples and real samples within a pixel are covered by a graphics primitive and a quantized alpha mask based on the alpha value to produce the pixel coverage mask; determine a link field that indicates links between the virtual samples and the real samples; adjust the link field based on the pixel coverage mask to link any orphaned virtual sample to one of the real samples, wherein each virtual sample inherits color data computed for the real sample to which the virtual sample is linked; and output the pixel coverage mask and the link field for the pixel. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20)
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Specification