Why matchbox window manager calls XRenderComposite from top to bottom?

[Olivier Fourdan]

Hi,

It actually renders the screen in two passes.

First pass from top to bottom, rendering only the opaque regions, while
adding up each opaque region to a global clipping region.

Second pass, from bottom to top, rendering only the translucent areas,
clipping out the opaque regions that it found in the first pass.

That's more efficient than rendering in a single pass from bottom to top.

FWIW, the logic is from xcompmgr, from Keith.

Cheers
Olivier


On Fri, Jul 10, 2020 at 11:06 AM 徐星 <openxu at gmail.com> wrote:

>
> Hi,
>
> Do you have any ideas why matchbox window manager render clients from
> top(near) to  bottom(far)?  I understand that the painter algorithm
> requires paints from far  to near.
>
>
>
>
> https://git.yoctoproject.org/cgit/cgit.cgi/matchbox-window-manager-2/tree/matchbox/comp-mgr/mb-wm-comp-mgr-xrender.c#n1619
> --
> NaCl!
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