Dr. Vanessa Freudenberg

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 ...

For high-quality prints you need high-quality screenshots. This means very high resolution, and nice anti-aliasing. Just grabbing the screen produces rather unpleasant results ( screenshot , 80 KB, 800x600 pixels). With normal OpenGL rendering you get rarely more than screen resolution, and anti-aliasing quality very much depends on your graphics board. So what to do? Tiled Rendering comes to the rescue. Instead of rendering the whole image at once, we render smaller portions of the scene, and then arrange the tiles into a large picture. However, just pointing the camera at each tile will not work as intended, the perspective would change from tile to tile. What is needed instead is to construct partial viewing frustums that together exactly recreate the whole frustum. This sounds like a lot of math, but actually it is quite simple: gluPerspective: fov aspect: aspect zNear: near zFar: far tile: rect | cotangent radians w h | radians := (fov/2.0) degreesToRadians. cotan...

We've been wondering for a while, why screen updates are more expensive than expected in the Tweak overlay. Now I debugged into this and it turns out we're uploading the whole texture even if only a small part was changed. The relevant code is in OGLTextureManager>>uploadTexture:dirtyRect: . A partial upload using glTexSubImage2D() is only performed if the texture in use is not static. Having found out what's going on it's easy to fix, a one-line change in TeapotMorph>>glRenderTweakCostume:on: does the trick: texCache isStatic: false. As simple as that - I just posted the update.