OpenGL and Plasma::Wallpaper

[Martin Gräßlin]

On Saturday 31 December 2011 12:10:37 Shaun Reich wrote:
> On Sat, Dec 31, 2011 at 5:17 AM, Martin Gräßlin <mgraesslin at kde.org> wrote:
> > On Thursday 29 December 2011 11:21:36 Justin L. Boss wrote:
> > Personally I am not a big fan of having animations which would require
> > OpenGL in the background. Most of the time the background is not visible,
> > it requires resources and puts load on the compositor which has to update
> > the scene although nothing changes (full repaints are most expensive).
> > 
> > May I ask why you want to use OpenGL?
> 
> Probably because QPainter is dog slow.
using OpenGL doesn't make it faster if you need QPainter to render to the 
background ;-)
> 
> Also, I don't think you should be against OGL wallpapers, considering
> some really sweet/impressive things could be done with them which
> could really make KDE stand out. e.g. a wallpaper playing a moving OGL
> scene, movies, virus wallpaper (which is currently a large CPU drain,
> and has no HW accel afik). Take Win 7 for instance, how they have
> "Dreamscene™" or whatever.
I divide the world into two categories: good for KWin, bad for KWin. An 
animated wallpaper is bad for KWin as it needs to update everything all the 
time. In that sense it does not matter whether the wallpaper uses OpenGL or 
something else. If it is animated than it is bad.

This is of course orthogonal to what it provides: being awesome. KWin has also 
the being awesome things which are in fact bad for KWin. But what's the 
difference? Nobody tries to use the desktop while the cube is spinning. It 
just doesn't matter that KWin is using lots of resources.

In case of a wallpaper covered by windows it does matter whether the 
background makes everything slow or not. So here I just think we should not 
give users the tool to make the desktop unbearable slow. Yes it looks awesome, 
yes new users might love it. Yes new users will switch back to whatever they 
used, because everything is extremely slow.

So unless our wallpapers learn to not redraw the areas which are not visible 
anyway (which is probably impossible to know for the wallpaper), I am not a 
fan of animated wallpapers in general.

Just for the record: using always animated wallpapers should perform better 
thanks to optimizations in 4.8.

Cheers
Martin
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