[cairo] [PATCH 0/5] Fix dashing with zero length dash intervals.

Carl Worth cworth at cworth.org
Fri Apr 14 10:15:49 PDT 2006

On Sun, 9 Apr 2006 23:10:36 -0400, Jeff Muizelaar wrote:
> The current implementation will render a zero-length visible segment as having
> zero length. However, the ghostscript rasterizer as well as acrobat both render
> these segments as they do zero-width lines -- 1 pixel thick.

Oh, so that's actually a problem.

Now that the zero-length dash stuff has landed I am getting a failure
for the new dash-zero-length test against the PostScript backend. The
claim of the test case is that butt-capped zero-length dash segments
should be invisible.

I like that semantic, as it is consistent with the fact that zero
width stroked lines in cairo are also invisible.

So this new failure is a bug in the PostScript backend since it's not
emitting something invisible.

In the case of zero-width lines, cairo's PostScript should be
consistent with cairo's "invisible" semantics because we catch the 0.0
case early up in cairo_gstate.c and don't draw anything.

So maybe we should do the same thing here, and at a high-level catch
the case of butt-capped dashing and filter out any zero elements in
the dash array. For example, a dash array of:

	[4 0 1]

would be replaced with:


when drawing with butt caps, (and should be left alone when drawing
with round or square caps).

What do you think?

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