[Xcb] xcb, xrender and thin lines

Keith Packard keithp at keithp.com
Wed Feb 15 00:37:07 PST 2006

On Wed, 2006-02-15 at 08:56 +0100, Vincent Torri wrote:

> For the xlib engine, raster uses XRenderCompositeDoublePoly for drawaing
> thin lines (and thin polygons too). That function is quite complicated and
> maybe there is a better idea. Does someone as an idea about how to do that
> with xcb, which maybe can be simpler ?

Far worse than complicated, that function is horribly inadequate for the
job of tesselating arbitrary polygons. I'm sorry I ever even considered
putting that into the Xrender library. You should stop using it
immediately to avoid catastrophe; it will generate garbage trapezoids
for seemingly benign input. It barely supports the polygons that xclock
generates, which was the only test application for that function.

Generating trapezoids for arbitrary polygons is a hard problem; cairo
still doesn't have a great algorithm in place for this (although we have
read papers about which algorithm we should implement).

keith.packard at intel.com
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