[cairo] Re: [Mesa3d-dev] OpenGL and Cairo

Jon Smirl jonsmirl at yahoo.com
Tue Apr 20 12:57:56 PDT 2004

I'll cc this over to the Cairo list. This will probably be a topic of discussion
at the xdev meeting next week. Any chance one of you OpenGL exports might come
to Boston? I'm not enough good enough at OpenGL to identify all of the issues.

--- Allen Akin <akin at pobox.com> wrote:
> My general concerns were that the semantics weren't a good match for
> what graphics accelerators (particularly fully programmable ones) do.....
complete text at bottom

This was my general conclusion too. I'm ok with creating a separate 2D API but
I'm concerned about how well it maps back into OpenGL. From my minor contact
with Cairo people I think they ignored OpenGL in the begining since OpenGL is
missing text support. Looking at Longhorn, xserver/cairo on top of mesa-solo (or
a closed source equivalent) is our only hope for competing. xrender isn't even

My choice would have been to optimize for OpenGL to the extent that it doesn't
compromise ps/pdf printing. Then I would have come back to the mesa group and
asked for mesa-solo and font support. 

If there are known problems mapping Cairo to OpenGL please let me know and I'll
make sure they get discussed. For example Cairo using a different model for
drawing gradients or curves could really mess up OpenGL performance. SVG has
this problem when mapping onto OpenGL.

Did you see these performance numbers for Cairo that were just posted?

On Mon, 2004-04-19 at 13:38 -0600, Soorya Kuloor wrote: 
> Hardware:
> ---------
> AMD Athlon64 3200
> 1.5GB RAM
> Graphics Chipset: ATI R350 NH (R9800)
> Software:
> ---------
> Fedora Core 1 (32 bit version)
> XFree: ATI's proprietary drivers downloaded from their website
> Display resolution: 1280x1024
> The numbers below are in frames per second as reported by the
> test. For full-screen numbers I just maximized the demo window.
> Test   backend       normal-size    full-screen
> ----   -------       -----------    -----------
> TRAP   image           9.2             2.2
>        xrender        11.8             2.9
>        glx           150.2           135.2
> GRAD   image           8.4             2.0
>        xrender         9.2             2.4
>        glx           125.4           103.0
> COMP   image           5.0             1.1
>        xrender         6.4             1.4
>        glx          2087.0           686.8
> TEXT   image          18.4             1.4
>        xrender        22.6             1.9
>        glx            61.8            49.4
> SHADOW image           2.1             0.35
>        xrender         2.62            0.5
>        glx           133.0           130.0
> The performance of the OpenGL back-end is really impressive. Obviously,
> the text caching problem that David mentioned slows down the OpenGL
> back-end considerably.

--- Allen Akin <akin at pobox.com> wrote:
> | So Cairo is our resticted set of operations.  Any opinions on the Cairo API
> | versus OpenGL 2D?
> My general concerns were that the semantics weren't a good match for
> what graphics accelerators (particularly fully programmable ones) do
> best; and too much of the design was duplicating functionality that
> already existed in the OpenGL world, but with slight incompatibilities
> that would force redundant implementation effort.  We can talk more
> about this stuff if you're really interested, but I don't want to waste
> time for people who aren't, so I'll leave it at that for now.
> Cairo seems to be a good response to what the UI folks think they want;
> but they admit that in general they're not experts in graphics
> acceleration, so what they want may not be a good match for where
> graphics accelerators are actually going.  From what I hear about
> Longhorn, Microsoft is trying to do a better job of bridging that gap.
> To be fair, a good bit of this disagreement concerns choosing what
> hardware you want to target, and the Cairo folks made a conscious
> decision to aim more toward systems without modern desktop-class
> accelerators.

Jon Smirl
jonsmirl at yahoo.com

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