Enabling GL_VERTEX_PROGRAM_TWO_SIDE

[wernermarius]

When writing to gl_BackColor inside a GLSL vertex shader, it is ignored as long as no call to glEnable(GL_VERTEX_PROGRAM_TWO_SIDE) was made. So the fragment shader's gl_Color always ends up with the value of gl_FrontColor.

Would it be a problem to enable GL_VERTEX_PROGRAM_TWO_SIDE by default (i.e. in GLRenderSystem::initGL) ?

[sinbad]

Have you tried this (in your GLSL)?

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#extension GL_VERTEX_PROGRAM_TWO_SIDE : enable

[wernermarius]

Have you tried this (in your GLSL)?

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#extension GL_VERTEX_PROGRAM_TWO_SIDE : enable

If I do that in my vertex shader, I get

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WARNING: 0:2: extension 'GL_VERTEX_PROGRAM_TWO_SIDE' is not supported

However, I have recompiled Ogre with a change to GLRenderSystem::initGL(), where I simpy call glEnable(GL_VERTEX_PROGRAM_TWO_SIDE) at the end. With that, everything works just fine (without adding the #extension... in my vertex shader).

[sinbad]

Ok - I think in practice this option has to be a material option rather than enabled globally, because otherwise it will change the behaviour of materials with culling set to off (two sided) where only the front colour is populated. You can of course continue to use your quick hack if you need it.

[wernermarius]

Yes, that sounds very reasonable. I will continue using my hack for the moment...