Compiz and Fedora

There was a big discussion about enabling compiz by default in Fedora on fedora-devel list a couple of days ago. Reading through the thread I realized that we never really communicated our plans here very well. I sent out the writeup below to explain a bit where we're going with Fedora and what the road blocks are, but I figured it wouldn't harm to also blog it.

We are working towards being able to enable a compositor by default.

Redirected direct rendering, Xv, Java problems, these are problems in the drivers and X server and affects all compositors. To get this done, we need to land a big chunk of code in the kernel (the DRM memory manager), we need to update the X server, the 2D drivers and the 3D drivers to take advantage of the new memory manager. We need to fix Xv. Hopefully the OpenGL support will broaden to support more chipsets (nouveau, avivo). Getting all this to a shippable state may take years, and in the mean time, the composited desktop, whether it's compiz, kwin4 or something else will only be an opt-in tech demo.

Once we get there, the default compositor will be compiz.

Some people can't get over on the wobbly windows and spinning cube, and claim it's over the top or apparently get nauseous. At the core, compiz is just a very efficient OpenGL redraw loop with a flexible plugin architecture. Compiz allows burning windows and spinning cubes, but we ship it in a very toned down default configuration that looks a lot like good old metacity. Consider xeyes; like wobbly windows, it's a neat tech demo and shows off the flexibility of X, but just because nobody runs xeyes for more that 2 minutes at a time that doesn't mean that X (or shaped windows) isn't useful.

A valid point about compiz is that it is not yet a great window manager. Metacity has a few years of head start there, but that doesn't mean that we can't fix compiz or that it'll be duplicated effort. For now, our (Red Hat) efforts have gone towards fixing the big underlying shortcomings in the X and OpenGL stack, which has left compiz in Fedora with a set of minor (but certainly annoying) windows manager bugs. Other spins (Fedora KDE or Fedora XFCE) can set up different default compositing managers, and they will of course benefit from the infrastructure work mentioned above.

We're not working on making metacity a compositing manager.

We tried it and decided that the metacity code base was not a welcoming place for a compositor. When we put down the work in metacity, the conclusion was to leave this very stable and well tested code base alone instead of injecting an OpenGL based compositor. The flip side of this decision is that we can now do a clean break in compiz and assume throughout the code that we're an OpenGL based combined compositing and window manager.

Compiz fusion and configuration tools.

desktop-effects is close to what we want to ship by default, perhaps we want to fold it into the new gnome-appearance-properties capplet as a new tab. The default compiz configuration and the set of options we expose outside gconf-editor is intended to be very conservative. At the same time, we want to allow installation of other compiz configuration managers and the compiz fusion plugins for people who like the tweak-ui kind-of tools.

Power consumption and other hand-wavey fud arguments.

Clearly running a 3D screen saver at the full frame rate is going to burn more battery than the blank screen saver, but that's not really relevant here. When idling, compiz and metacity use exactly the same amount of power. There are no code paths anywhere in the stack that "turn on 3d powerplanes". My bet is that it's more power consuming to wake up all applications to redraw their exposed areas under the window you're dragging than it is for compiz to just recomposite that out of textures already in video memory.