Anyone managed to get 2-sided GLSL lighting working in QC? I'm
actually trying to implement a very simple 'fake' lighting effect in
a GLSL Shader patch, whereby the colour at each fragment is a
product of it's distance from an arbitrary light-source position. I
have this working already, but I'd like to be able to shade the
front and back-facing sides of a mesh with different base-colours.
I've tried using
gl_FrontColor
and
gl_BackColor
set to different colours in the Vertex Shader, but the front color
is always used for both faces, even if I embed the GLSL Shader patch
inside a Lighting Patch with the 'Use 2-sided lighting' option
enabled.
2-sided lighting doesn't deal with gl_BackColor, it only determines
whether or not certain lighting calculations are performed on non-
front-facing polys. If it were to set gl_BackColor, there'd have to
be another input somewhere to control it (gltools feature request? ;)
You can see the effects of it here -- 2 teapots, both with front-
facing polygons culled. The left one is "normal" lighting, the second
is "2-sided". Otherwise, they're identical. Note the inner specular
highlights on the right teapot -- that's what this does.
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