[cairo] Dia as a new Cairo testbed
keithp at keithp.com
Mon May 24 18:05:10 PDT 2004
Around 0 o'clock on May 25, Hans Breuer wrote:
> To get an educated opinion about current abilities of Cairo I've written a
> Dia  export filter based on Cairo. The source of it is already in gnome
> cvs, it even is integrated in the *NIX build process : ./configure --with-cairo
Cool. We'll try to figure out where the remaining problems are. I tested
the .svg file with the cairo-based 'xsvg' program which generated different
(The images in this version don't appear at all because the svg-cairo
library doesn't handle them yet).
> The arc drawing is completely bogus. [Doing a simple cairo_arc()
> produces arcs mirrored against the horizontal axis and all my tries
> with cairo_arc_negative() and angle juggling have failed, too.]
I think you haven't quite got the arguments for these functions figured
out; xsvg draws this figure correctly.
> Linestyle in bezier lines are apparently not supported yet
Yup. It's not a huge amount of work, but it is yet to be done.
> Image rendering is not as good as expected (At least I would
> expect it to reproduce similar quality as in the pixbuf case
> when using CAIRO_FILTER_BEST).
We're just using bilinear interpolation. Anisotropic filtering would
generate better results.
> Rendering of alpha images is completely broken. Maybe caused by
> not properly using the Cairo Operator.
Perhaps this is a confusion with the premultiplied alpha format which
cairo uses. libart uses non-premultiplied alpha (I'm pretty sure). This
may also be causing troubles mentioned above?
> Text rendering is known to be limited in Cairo (the so called 'toy api'
If dia uses pango for text rendering, we should be good to go once there's a
cairo backend for pango.
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