Posted by Xerxes Rånby on Nov 04, 2015; 8:58am
URL: https://forum.jogamp.org/Unable-to-draw-to-GLOffscreenAutoDrawable-on-Raspberry-Pi-2-tp4035723p4035728.html

your example do not show when you call getImage.
I would recommend you to call getImage from within display(GLAutoDrawable drawable)
gl may be undefined if you call getImage outside display.