It controls the quality of the upsampling filter. This can help a lot
if heavy scaling is needed to maintain performance, it also helps if
MSAA is not enabled.
There are 3 quality levels, low, medium and high. 1, 4 and 9 bilinear
taps are used for each level respectively. The high quality setting
employs a tent filter.
Pixelflinger
8866e2829f