GLSLtryout is the main program of a jogl/GLSL image convolve example,
adapted from various code on the web:
- redbook checkers program (gl texture mapping)
- jglmark (jogl/glsl interface)
- http://www.ozone3d.net/tutorials/image_filtering.php (glsl convolve)


you will need to rewrite the image loading code (routine tobyte3)
and use a square power-of-2 texture image.