Re: [E-devel] RFC gradient clip

[Carsten H. (T. R. <ra...@ra...>]

On Tue, 8 May 2007 14:42:37 -0300 "Gustavo Sverzut Barbieri"
<bar...@gm...> babbled:

> I want to know how difficult would be to implement support for clip
> using gradient objects.
> 
> Motivation to do so is to have clip border as fade out instead of hard
> "cut". We need it for our software, Canola, but talking to Freevo guys
> show the same problem.
> 
> I've already talked to raster about this issue and he suggested
> creating an overlay image with a copy of the background with alpha
> channel changed, but then comes the question raised by Tackaberry
> (freevo dev) if the background changes a lot, it couldn't be just one
> image, but the rendered background so far. How does it behave to
> retrieve rendered scene in different backends, like GL?
> 
> We are willing to implement it if you give us some hints :-)

it's not as easy as it sounds. what you want is "generic clipping" to an mask.
that has been on the "will do it one day" list for a long time. so RFC-wise -
"absolutely". but implementing it so its vaguely efficient will need some work.
any mask needs to be rendered first, THEN used when compositing objects. right
now evas has no "clip buffer" mode (all objects clipped are clipped WHEN they
are rendered, instead of being rendered to a temporary buffer first, then
clipped when finally composited to the screen). for now its "clip when you
draw" method is ok for most uses, but we still need it implemented.

to implement this we will need (imho) the "tile cache" i suggested. something
that lets you generate a surface from sources and cache just regions of it
(tiles) that are needed. this means you don't re-generate it for every object
clipped to it that needs a draw, but will allow us to cap the memory usage of
such regions during a draw.

but before leaping into this - note, this is not so "simple" as it needs
implementing across multiple engines and graphics api's.

> -- 
> Gustavo Sverzut Barbieri
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-- 
------------- Codito, ergo sum - "I code, therefore I am" --------------
The Rasterman (Carsten Haitzler)    ra...@ra...
裸好多
Tokyo, Japan (東京 日本)