Grimrock

I am trying to alter some dif-maps. But sometimes I got some ugly edges with grafics that go into transpareny. It seems that ingame transparency is rendered differently. In various graficprogramms everything looks fine.

I am using Gimp and save to BC3/DXT5

Does anyone have an idea, what I am doing wrong?

If the blend mode is "Opaque" then you only get 1-bit alpha with alphaTest = true, or no alpha at all with alphaTest = false. If you need alpha blending you need to use "Translucent" blend mode but the material cannot be lit in this case.