Comment # 4 on bug 107428 from Isaac Curtis

The bug has been identified. It can be seen on Lines 40-53 of
https://github.com/OpenRA/OpenRA/blob/bfcbe8c0043bfadd1b38c4987f133e29aa54275c/glsl/shp.frag

Basically, it was a floating point comparison bug. It checked for samplerIndex
a float that takes int values, against 1.0, 2.0, etc. However, sometimes 1 is
less than 1 due to floating point issues. Changing samplerIndex < 1.0 to
samplerIndex < 0.5 fixes the issue.

It turns out that AMDGPU drivers seem to be the only implementation that
experience this particular issue. 

This case is resolved. I don't see anything to fix in the drivers here.