sin hash  non-finite  73.9%   distinct values per 64x64 tile at y=0,700,1400,2700: [6, 2, 0, 0]
IGN       non-finite   0.0%   distinct values per 64x64 tile at y=0,700,1400,2700: [31, 31, 31, 31]
blue tile wrong texel  38.7%   (rows past y=2048 can no longer be told apart at half precision)
gl_FragCoord.y exact up to y=1024