Method and apparatus for simplified anti-aliasing in a video graphics system

A processor, wherein the processor determines Z values for a fragment in an anti-aliasing video graphics system, the processor comprising:

• a processing module;
• memory operably coupled to the processing module, wherein the memory stores operating instructions that, when executed by the processing module, cause the processing module to perform the functions of:
• sampling the fragment to produce a mask including a plurality of samples, wherein a valid sample indicates coverage of a pixel by the fragment at a portion of the pixel corresponding to the valid sample, wherein the fragment sampling includes;
• determining a Z value at a reference of the pixel,
• determining slopes of the Z value with respect to the reference point, and
• determining a Z value of a front most valid sample of the plurality of samples in a manner that includes determining which of the pixels is the front most valid sample based on the slopes, position of each of the plurality of samples with respect to the reference point and the mask;
• and
• calculating the Z value of the front most valid pixel based on the position of the front most valid pixel in relation to the reference point, the slopes and the Z value at the reference point, wherein the Z value of the front most valid sample represents spatial depth of the fragment at the point within the fragment corresponding to the front most sample;
• and
• utilizing the Z value of the front most valid sample as the Z value for all samples in the plurality of samples.

A video graphics circuit, comprising:

• a setup engine, wherein the setup engine produces primitive slope information based on received graphics primitives;
• a raster engine operably coupled to the setup engine, wherein the raster engine generates pixel fragments from the primitive slope information, wherein each pixel fragment includes:
• a color value;
• a set of coordinates indicating a pixel in a display frame to which the fragment corresponds;
• a mask value that indicates coverage of the pixel by the fragment, wherein coverage is indicated by set bits in a bit field corresponding to a predetermined sampling pattern that includes a plurality of samples, wherein the raster engine produces a plurality of samples of the fragment, a subset of the samples corresponding to the set bits in the bit field are valid samples in that they are within the coverage of the pixel by the fragment;
• and
• a Z value for the fragment, wherein the Z value represents spatial depth of a front most valid sample of the fragment, wherein the Z value is determined by:
• determining a Z value at a reference point of the pixel,
• determining slopes of the Z value in two directions with respect to the reference point,
• determining which of the pixels is the front most valid sample based on the mask, the slopes, and the position of each of the plurality of samples in the predetermined sampling pattern with respect to the reference point, and
• determining the Z value of the front most valid pixel based on position of the front most valid pixel in relation to the reference point, the slopes, and the Z value at the reference point;
• a pixel pipe operably coupled to the raster engine, wherein the pixel pipe performs texture mapping operations on the pixel fragments to produce textured fragments;
• a frame buffer that stores color and Z values for a plurality of pixels included in a frame;
• and
• a render backend block operably coupled to the pixel pipe and the frame buffer, wherein the render backend block blends textured fragments with corresponding pixels in the frame buffer as determined by the set of coordinates for each textured fragment, wherein the Z value for a textured fragment is used to blend all valid samples in the textured fragment.