Hi, I set specular to 1.0 and shininess to 128 and I get a nice
effect on my
surface when I use a non-white surface color. Then I apply a texture
and the
shining effect disappears. How to keep it?
This is because the shading model in standard OpenGL is done before
texturing, so the texture overlays the specular highlight, which isn't
what you naturally expect to happen.
effectively you get (diffuse + specular) * texture
when you want (diffuse * texture) + specular
Three ways I know of getting around this.
1) Old School: Do 1 pass that has ambient and diffuse at normal, with
texturing, but no specular. Do 2nd pass with zero ambient and diffuse,
no texturing, but with specular. Blend it on so as to add the two
images together.
2) Semi-Old School: OpenGL 1.2 Added GL_SEPARATE_SPECULAR_COLOR. Using
this you can separate the specular colour out, and add it at a later
stage in the pipeline
3) New School: Vertex shader that does the lighting calculations, but
forwards the diffuse and specular colours separately to the fragment
shader. Fragment shader that does diffuse * texture + specular. If you
do this then you can do per-fragment lighting rather than per-vertex
and it looks that much better.
Easiest on to get going is No. 2. I think it's just a glEnable() call
to get it working. For number 3 take a look in the Orange book (I've
never read it, but it must be in there)
Paul
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