I am using Mesa 4.0.1 on MS Windows 98. I have set up a window with an 8 bit alpha buffer (confirmed by checking glGetIntegerv(GL_ALPHA_BITS) ). Whenever I use glReadPixels, the alpha component is returned as 255, despite having set it differently. This problem also ocurrs with trying to blend using GL_DST_ALPHA, it is as if the alpha buffer were full of 1.0f.
Does anyone know a fix for this?