I have an app where I am trying to render an image to a pbuffer, then save that
image to file. I call gl.glClearColor(0, 0, 0, 0) to make a black, transparent
background. After this, I render a few shapes and try to read the rendered
image back with gl.glReadPixels(0, 0, w, h, GL.GL_RGBA, GL.GL_UNSIGNED_BYTE, b).
However, the read back result suffers from a complete lack of transparency.
Even those places which I would expect to be transparent because nothing was
drawn there. Every pixel in the populated data buffer has an alpha of 0xFF.
This does not seem like correct behavior.
My system is a newer workstation class machine with an nVidia Quadro FX graphics
card, running windows XP. Test done with JSR 231 1.1.0 on java 1.6 JDK, run
from within eclipse. If any of that info is helpful.