desktop-shell: How to enable really alpha blending of weston background?

[Pekka Paalanen]

On Mon, 22 Feb 2016 21:36:41 +0900
YoungJun Jo <dtoartist at gmail.com> wrote:

> Environment
> OS : Linux kernel 3.10
> Version : Weston 1.8.0
> H/W spec : embedded soc based on ARM
> 
> Hello, All
> 
> I have a question about weston background.
> I want enable alpha blending to background, so i have typed
> 'background-color=0x00ffffff' on weston.ini.
> But that's not really alpha blending. Because alpha value of pixel is a
> 'ff'.
> My chips have four H/W layers, top of the layer is UI layer and second
> layer is video layer.
> 
> I reviewed source code of 'desktop-shell.c' but i can't find any hints.
> 
> Need some additional ideas to solve this problem. Any feedback is
> appreciated.

Hi,

Weston does not do transparent backgrounds. The backends instruct the
renderers to allocate an opaque framebuffer if possible, because there
is not supposed to be anything "behind" Weston. After all, Weston is in
charge of everything going to the display, so by definition there is
nothing to show through to.

IOW, the decision to use an opaque framebuffer is in each backend code.
I suppose you could change that if you wanted to: the Pixman format for
pixman-renderer, or opaque_attribs vs. alpha_attribs for the
gl-renderer.

What are you *actually* trying to do?


Thanks,
pq
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