OpenGL embedded in gtk has colour badly displayed: shader at fault?

Question

Note that this is a re-write now that I have more clues as to where the problem could be...

I am creating a GTK GUI which contains two embedded OpenGL displays. Both use the same shader code (complied once for each). On my normal hardware, this works fine. On a virtual machine running on the same hardware, I get horrible colours -- see images.

I suspect that the shader code is at fault -- certainly dropping a simpler shader does make the problem moot. However, I do need both diffuse and spot lights in my shader thus making it non-trivial.

Anyone has seen this before?

Answer 1

The shader code was at fault. It was doing too much in the wrong place and was crippling the GPU on the virtual machine. A different shader code made things work fine.

Answer 2

It looks like the issue is that you draw the text in yellow, then it's still yellow when you draw into the next buffer. My guess is that you need to reset some state each time you draw.