[cairo] PDF Backend for cairo

[Carl Worth]

On Tue, 30 Nov 2004 21:37:20 -0800, Keith Packard wrote:
> The X solution here is to construct a mask holding all of the trapezoids
> and then use that to draw the final object.  Using an ADD mode for merging
> the trapezoids together ensures that solid figures end up without seams.

Kristian and I looked at a similar problem with seams in his output
yesterday. (The seams were showing up in acroread only after enabling
the "Smooth line art" preference). Kristian switched from filling
individual trapezoids to a single fill of a complex path containing many
trapezoids and the problem went away.

> Can you create a temporary alpha mask in PDF?

The stuff we were looking at yesterday was all opaque. As we look at
transparent objects there may yet be problems that aren't solved by the
default rules for filling complex paths. If so, PDF provides
"transparency groups" that should allow the full control necessary for
the intermediate combining of seam-free trapezoids.

-Carl