Idea how to fix slow window resize in a composited desktop

[Dennis Kasprzyk]

Hi,

I think that I have found a solution for the slow window resize in a 
composited desktop environment. I don't know enough about the xserver 
internals to say that my idea will work, but I would like to share it with 
you.

To prevent the need the reallocation of new window pixmaps on the xserver side 
and it's handling on the composite manager side during a frequent window 
resize, we could redirect the drawing of the window to a pixmap that is 
bigger than the window:

- The composite/window manager uses XCompositeNameWindowPixmap for the normal 
window handling.
- If the user clicks on a window edge (=wants to resize a window), then the CM 
creates a big (screen size?) pixmap and calls a new 
XCompositeAssignPixmapToWindow function and frees the old window pixmap.
- The xserver copies the content of the window to the new pixmap and redirects 
all drawings to the new big pixmap.
- As long the window fits into the big pixmap all resizes will directly go 
into it. If the window gets bigger than the current assigned pixmap, then the 
CM will need to create a bigger pixmap or switch to the current 
XcompositeNameWindowPixmap handling.
- If the user releases the window edge (=terminated resizing) then the CM can 
call XCompositeNameWindowPixmap to get a window sized pixmap and can free the 
big one.
- The xserver can then copy the window content from the big pixmap to the new 
window sized pixmap.


Dennis Kasprzyk