Why matchbox window manager calls XRenderComposite from top to bottom?

[Xing Xu]

Thanks a lot. I understand how the Opaque window is composited. But as to
the translucency window, it starts composite from the first translucent
window (the first translucent when searching from top to bottom), then to
the top.   But if there are any other translucent windows between
first translucent window and the bottom window, should this be considered?

Olivier Fourdan <ofourdan at redhat.com> 于2020年7月10日周五 下午5:12写道：

> 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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