Is it possible to accelerate somehow wallpaper painting?
I haven't found how to do it with QPainter.

Is there some ways to accelerate with compositing turned on?

There is a video wallpaper plasma plugin, but it eats too much cpu (copy every frame and repaint the whole screen...)

//Dreamscene for windows has good performance

Unfortunately, due to a limitation of the Plasma Canvas used for painting efficient methods for painting such as XCB are unavailable...

ok, another idea.
is it possible to make parts of desktop window transparent (wallpaper)?
then it's possible to use kwin effects api for doing this - draw animated wallpaper on the "pre-paint window" stage

If you implemented what was required using a Plasma::Wallpaper plugin which did the needed drawing ( or lack of drawing ) then it would be possible to draw the animated wallpaper on top yes.

Note that integrating the animation itself directly into Plasma through a Plasma::Wallpaper would be more strongly recommended and least likely to break.

yep, I understand that... but you've said it's impossible to draw something on a wallpaper in an efficient way.

My question - how do I make "wallpaper" parts of desktop window transparent? (some plasmoids are transparent, the must be painted after the wallpaper is)

The likely solution would be to have a Wallpaper which drew only a transparent Alpha channel as the desktop, then used Compositing to place another window behind Plasma ( As it sets itself as the root window in X though, not sure if this is possible... )