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.

Abstract: Circuits, methods, and apparatus that perform cylindrical wrapping in software without the need for a dedicated hardware circuit. One example performs cylindrical wrapping in software running on shader hardware. In one specific example, the shader hardware is a unified shader that alternately processes geometry, vertex, and fragment information. This unified shader is formed using a number of single-instruction, multiple-data units. Another example provides a method of performing a cylindrical wrap that ensures that a correct texture portion is used for a triangle that is divided by a “seam” of the wrap. To achieve this, primitive vertices are sorted such that results are vertex order invariant. One vertex is selected as a reference. For the other vertices, a difference is found for each coordinate and a corresponding coordinate of the reference vertex. If the coordinates are near, no change is made. If the coordinates are distant, the coordinate is adjusted.