Not very long ago I mentioned that Frogatto’s iris transition effect didn’t work with the ATI R600 KMS drivers, and I assumed that this was caused by some lacking in the Mesa code. I even filed a bug report to its developers about it.

I was wrong. As MostAwesomeDude explained to me on IRC, and later posted in the bug tracker:

In UMS mode, r600c provides 8 bits of stencil on all configs, but in KMS mode, the normal wider variety of configs are available. The app used to have a call to SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 1), but it was commented out for some reason. Uncommenting that line caused a stencilled config to be properly selected.

The moral: Always check your GL configs.

Effectively, we discovered that restoring that line would solve the issue. It was apparently commented out by Dave at some point by accident. This won’t matter for long anyway, since Frogatto is already using a different mechanism to render the transitions on SVN trunk, solving the missing effect on who knows how many PC configurations. The iPhone port also lacked these transitions because of a platform limitation, so maybe the new technique will solve that minor shortcoming as well.

So now I’m basically just waiting for a new official release of the Tux-On-Ice patch for Linux 2.6.35 before switching to a complete KMS-based configuration. Until that happens, I’ll continue using 2.6.34.4 in UMS mode.

Again, thanks to MostAwesomeDude for the help with finding the cause of the bug!