[Pixman] [PATCH 1/3] Add CLEAR and SRC linear interpolation operators

Taekyun Kim podain77 at gmail.com
Mon Sep 19 00:00:01 PDT 2011

On 09/17/2011 12:29 AM, Søren Sandmann wrote:
> Chris Wilson<chris at chris-wilson.co.uk>  writes:
>> On Thu, 15 Sep 2011 13:26:09 +0200, sandmann at cs.au.dk (=?utf-8?Q?S=C3=B8ren?= Sandmann) wrote:
>>> Chris Wilson<chris at chris-wilson.co.uk>  writes:
>>>>> Did you see Taekyun Kim's reply to this? He proposes this API:
>>>>>       pixman_image_composite_xrender(op, src, shape, clip, dst)
>>>>>       pixman_image_composite_bounded(op, src, shape, clip, dst)
>>>>>       pixman_image_composite_simple(op, src, shape, clip, dst)
>>>>> instead, which would add direct one-pass support for all of cairo's
>>>>> compositing schemes, including clip masks.
>>>> You're encoding operator semantics into the function call and adding
>>>> parameters for the rest?
>>> Yes, basically. It's more or less a direct translation of the three
>>> compositing equations that cairo uses into function calls.
>> But why three functions when the difference is the semantics of the
>> operator. Just allow Cairo to pick the operator that corresponds to Cairo's
>> interpretation of op + mask + clip.
> I guess that makes sense. I'll take a look at the patch sometime next
> week.
> Soren

What I think as "best" is that pixman can take "compositing expression tree"
via either "compositing program" or "deferred compositing (like GPU)".
Those three interfaces are just examples of compositing equations pixman
can support for cairo by introducing some additional features i.e. LERP.
My question is then "such extension might be sufficient or not".

What I want to achieve is that "plot a pixel if and only if it is 
visible". I believe
we need compositing expression tree to achieve this. That would be the right
direction in the long run.

Anyway, for our current purpose, encoding semantics into OP seem to be a
better way. I'm not opposed to this and I will make fast paths for LERP 
if these
patches get in upstream.

Best Regards,
Taekyun Kim
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