With a GL_LINE, is there a way to have the vertex (or geometry) shader treat the first and second point differently?
i.e. In a line from p0 -> p1 I'd like to apply a different transform to p0 than to p1.
I know how to do this with a computer shader, but I was wondering if there is a way to do it with a vertex/geometry shader.
If, in your case, you want to treat all even numbered vertices different from all odd numbered vertices, then you could use gl_VertexID built in GLSL variable.
You could pass in two modelviewprojection matrices, one for type A and one for type B, and apply the one based on the least significant bit of gl_VertexID.
if ( gl_VertexID & 1 ) ...
If there is no fixed pattern for which vertex number gets which treatment, then you just need to add an additional vertex attribute like DMGregory proposed.
If you don't want to do that, and if you are passing 4-float coordinates with x,y,z,w you could even encode the special treatment in 'w', and reset it to '1' after detecting the special case. (Or even hack in a large offset in x to signal this. But that's the ugliest option.)
gl_VertexID in my geometry shader, but I got an error saying it's not available in my current profile. I'm stuck using geometry shaders instead of vertex shaders right now because I'm using multiple viewports with geometry instancing. Anyways, I'm going to try your second suggestion. Thanks!
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#version specified in your shader source.
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QOpenGLFunctions_4_3_Core. I do begin my shaders with #version #430 I try to keep it pretty basic because I've had issues in the past where after getting stuff working on Linux, I'd move to Windows just to have it say it doesn't support a bunch of stuff.
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gl_VertexID is not available in geometry shaders.
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