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List:       kwin
Subject:    Re: Compositing manager
From:       "Matias Valdenegro T." <hunts () igloo ! cl>
Date:       2006-07-14 22:07:10
Message-ID: 200607141807.10993.hunts () igloo ! cl
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El Friday, 14 de July de 2006 15:24, Thomas Lübking escribió:
> Am Freitag, 14. Juli 2006 19:23 schrieb Matias Valdenegro T.:
> > I don't agree that Effects should work in all scenes, as OpenGL
> > compositing is very different in implementation and capabilities as
> > XRender compositing (See Shaders and GLSL).
>
> well, i do =)
> YES. XRender support is (currently more than) poor. Even nVidia's is broken
> on 7.1
> YES. XRender doesn't support shaders - but openGL < 2.0 (afaik) neither
> (you'd need to call some shader language. If i missed the part in the
> latter OpenGL API (i think the latest a took a look on was 1.3) -
> apologises, and please correct me)

Right, but most cards (2003 - 2004 at least) supports Shaders, and just using 
an extension or direct driver support is sufficient for using them.

Even without shaders compositing is easy, i can create an API for that.

> However,
> 1. OpenGL won't be /real/ fun before a X server on top of OpenGL (like EGL)
> is (commnly and fully) avaliable (or the texture from pixmap extension is
> übergood)
> 2. XRender could be accelerated in the future (i don't really believe
> anymore, but who knows...)

I hear that every year :)

> 3. It's probably easy to maintain XRender code (especially on a high level
> API, such as for a plugin ;) - it will just be damn slow unless you've got
> XRender acceleration (and it's done in SW)

Actually it might be, but i don't think so.

Besides, how many people are using XRender and how many are using OpenGL? The 
latter overpasses XRender by much.

Anyway, an interesting question to ourselves is "Why everyone (Compiz, AIGLX, 
glcompmgr, etc) is using OpenGL and dropping XRender?

> > As i understand, shadows are just an image that gets composited along the
> > window, producing a bigger image that gets composited to the desktop.
>
> You'll be in trouble for arbitrarily shaped windows using this technique.
> For arbitrary shadow i'd propose (on infrastructures with accelerated
> scaling) to create the shadow by generating n (0,0,0,1/n) copies of the
> shape matrix (where a is the alpha value of the window), scale them by
> 1+f*n/i (where i is the copy index and f is the shadow size factor, maby an
> exponetial function will look better) and blend them over each other (and
> good god, cache this in a texture/pixmap and only update if the window is
> rescaled =) as this is by far faster than a proper gaussian blur (that
> could really stress the CPU for big windows)

Yep you're right, interesting approach.
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