Friday, February 16, 2007

OpenGL in a Workspace

On some modern Linux systems, Croquet does not work anymore because OpenGL failes to initialize. Now, I originally wrote that code, and it worked fine for years. So it can't possibly be buggy, right? Jens Lincke of impara tracked it down to the "Composite" extension that is enabled by default nowadays. With Composite disabled, it works, enable it, and it does not.

So I turned to NVIDIA for help, thinking their driver might be buggy. Had to give them an easy way to reproduce the problem, this is the snippet I came up with:
| ogl green |
ogl := OpenGL newIn: (0@0 extent: 100@100).
green := 1.
ogl glClearColor(0, green, 0, 1).
ogl glClear(16r4000).
ogl swapBuffers.
Sensor waitClickButton.
green := 1 - green.
] repeat] ensure: [ogl destroy]
Beauty, eh? ;-) I guess nobody has done this in a workspace for a long time. Stop it with Alt-.

Anyway, NVIDIA could reproduce the problem, and found our bug:
[...] the app is trying to create a depth 24 child window of a depth 32 parent and the app specifies neither a border pixel nor a border pixmap.
Doh! I forgot to specify the border! We were just lucky that this did not happen before. Jens and y.t. made a patch, should be in the next VM. And big thanks to NVIDIA developer support!