Dither

The Pixel Engine uses a 4×4 perfect-magic-square matrix when DstMode.DitherEnable is set.

Y / X	0	1	2	3
0	0	12	3	15
1	7	11	4	8
2	13	1	14	2
3	10	6	9	5

DitherOffset adds two-bit offsets to the low two integer bits of X and Y, modulo four. This preserves the dither pattern when a window moves.

Let d be the selected matrix value. The reduced-width component calculations are:

Color6 = min(Color8 + (d >> 2), 255) >> 2
Color5 = min(Color8 + (d >> 1), 255) >> 3
Color4 = min(Color8 +  d,       255) >> 4
Color3 = min(Color8 + (d << 1), 255) >> 5
Color2 = min(Color8 + (d << 2), 255) >> 6

Sources: Technical Spec, p.34, Technical Spec, p.35