[compiz] state of blur plugin

[David Reveman]

I forgot to give everyone an update on this.

The blur plugin is in a reasonable state now. It requires an OpenGL
implementation with an accelerated CopyTexSubImage2D path for usable
performance and that's likely not going to change sometime soon. One
major performance improvement can still be made, which allow us to avoid
the CopyTexSubImage2D path whenever the area behind a blurred region is
a solid window. However, there's a lot of special cases to such an
optimization and I reckon that it will be error prune so I'm considering
not to try and add it myself. If someone else likes to give it a shot,
I'll gladly look at any patches and include them if it proves to work
well.

Some additional options have been added to the decorators which allow
you to make any translucent decorations blur what's behind them.
Applications can also use the hint recognized by the blur plugin to
specify blurred regions.

I've added two small utility programs to git.compiz.org:

git.compiz.org/blurset
and
git.compiz.org/blurdemo

blurset, is similar to transset except that it allow you turn on/off
blur behind translucent parts of any application window.

blurdemo, is just a simple gtk example app that uses the blur support
provided by the blur plugin.

So all the hard work needed for a proper blur plugin should be done now
and the fun and easy part with adding additional filters is left. I only
put the simplest possible filter I could come up with in there for now
and it doesn't do much blurring at all. I'm interested in patches that
add additional filters.

- David