Efficient Z testing

Abstract

Z testing during computer graphics rendering is performed in a manner so as to optimize rendering. The status of a pixel as non-promotable may be tracked using a pixel status array (PSA). Each PSA row may contain bits which correspond to the non-promotable status of pixels. Each row may include five pixels, the first four of which represent the pixels in a subspan. If the row corresponds to a valid subspan, a determination may be made as to whether any pixel in the subspan is represented by a one, indicating that the pixel is non-promotable. This row corresponds to a previous subspan that has been sent down rendering pipeline. If a one is present, then the current subspan may be stalled until the pixels of the previous subspan has gone through color calculation. If, in the row that has just been read, no pixels are represented by a one, then a determination may be made as to whether any pixels in the current subspan are non-promotable. If so, then the corresponding bit in the current PSA row may be set to one. Otherwise, the Z test may be performed on each pixel of the current subspan.

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