(1) Suzanne's normal map is actually linear but we were telling GL that
it is SRGB, so the shader was not reading (0.5,0.5,1.0) from a perfectly
flat normal map.
(2) --linear in mipgen was not honored when consuming PNG files.
(3) The build was not passing --linear to mipgen for the normal map.
d3e7103ee5
