Posted by jmaasing on May 02, 2014; 11:35am
URL: https://forum.jogamp.org/off-screen-rendering-jogl2-tp4032257p4032259.html

AWTGLReadBufferUtil extends GLReadBufferUtil so look in the parent class.

http://jogamp.org/deployment/jogamp-next/javadoc/jogl/javadoc/com/jogamp/opengl/util/GLReadBufferUtil.html#GLReadBufferUtil(boolean,%20boolean)

Although I don't know more than that, maybe there is some pre-multiply with alpha going on somewhere for the off-screen buffer.