[compiz] Blurring behind windows

[Mirco Müller]

Am Donnerstag, den 04.01.2007, 20:01 +0100 schrieb julio at lepi.org:

> Maybe you assume too much ;)

Possibly, but I have such a feeling...

> Imagine you have on current compiz 9 firefox windows open, maximized, and
> each one with a very low transparency. Does that make compiz (or the whole
> system) crawl? No.

	That would mimick just _one_ window following your approach. I not
seldomly have 10 open/mapped windows around (many at least have
screen-size... area-wise). Instead of dealing with 10 textures for those
windows I would then have 9 times the texture-lookups operations needed
to draw all those windows. While that might not matter to owners for the
bigger GeForce-cards, people on intel-"cards" (the integrated graphics
with shared memory) will run out of texture-fillrate pretty quickly.

> A quick test I made:
> http://ghanima.alarue.net/gallery/compiz/Screenshot_001
> Here are 9 galeon windows opened, each one with a 9 percent transparency,
> with a movie playing behind them. Xgl remains at 12% of CPU use.

	BTW, the offset will have to be smaller for the actual implementation
to verify your approach. But I guess you just didn't place them close
enough before making the screenshot to approximate the look of your
idea.

> I don't think making blur that way would mean uploading the same texture
> multiple times.

	I did not mean uploading in the sense of "move from system memory to
GL-cards memory". That's what GLX_EXT_texture_from_pixmap is for to
avoid.

	I should have phrased that more precise. What I meant was there would
be additional setup work needed for the multi-texture mode and I do not
know how much overhead that will create. But I do not think this to be
cheap. This will need to happen on every configure- and map-event.

> Why not give it a chance?

	Anybody is free to try that of course. But I would not recommend it and
that's only my opinion. 

> Anyway, nobody said that using blur on large regions of the screen would
> be costless.

	Well, I just have the feeling it will be too costly. I do not expect
blurring to be cost-free at all :)

Best regards...

Mirco "MacSlow" Müller

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