If all MSAA positional samples are covered by the fragment, the
shading sample is evaluated at the center of the pixel. If instead the fragment covers
fewer positional samples, the shading sample’s position can be shifted to better
represent the positions covered. Doing so avoids shade sampling off the edge of a
texture, for example. This position adjustment is called centroid sampling or centroid
interpolation and is done automatically by the GPU, if enabled. Centroid sampling
avoids off-triangle problems but can cause derivative computations to return incorrect
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