Bug 26010 - cairo_line_to optimizes away path segments
Summary: cairo_line_to optimizes away path segments
Status: RESOLVED FIXED
Alias: None
Product: cairo
Classification: Unclassified
Component: general (show other bugs)
Version: 1.9.4
Hardware: All All
: high critical
Assignee: Carl Worth
QA Contact: cairo-bugs mailing list
URL:
Whiteboard:
Keywords:
Depends on:
Blocks:
 
Reported: 2010-01-12 08:07 UTC by Alois
Modified: 2010-01-12 14:35 UTC (History)
1 user (show)

See Also:
i915 platform:
i915 features:


Attachments

Description Alois 2010-01-12 08:07:36 UTC
If I draw (with cairo_line_to() calls) a path which contains segments which
are draw twice, these segments are not rendered when the path is stroked.

Example:
cairo_move_to(1,1)
cairo_line_to(1,2);
cairo_line_to(2,3);
cairo_line_to(1,2);
cairo_stroke();

The same happens when I use rel_line_to().

This bug did not exist in cairo 1.8.8

Because of improved PDF handling I need to switch to a newer cairo version
than 1.8.8 and wouldbe very happy if this bug could be checked and fixed.

Thank you
Comment 1 Chris Wilson 2010-01-12 09:09:00 UTC
Thanks for the bug report!

commit 74ea4c908067f5579b51d3dbaea387da8f343671
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Tue Jan 12 17:00:25 2010 +0000

    path: Do not remove anti-parallel line segments in case we are stroking
    
      Bug 26010 - cairo_line_to optimizes away path segments
      http://bugs.freedesktop.org/show_bug.cgi?id=26010
    
    As exercised by path-stroke-twice, we incorrectly optimise away a line
    segment if the path doubled back upon itself. This is very reminiscent
    of the optimisation bug for replacing curve-to with line-to.

commit a5dd5a6069c0d7435260a954d8d98483f5fbcc1c
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Tue Jan 12 16:32:09 2010 +0000

    test: Add path-stroke-twice
    
    Exercises a bug found by alois@astro.ch, whereby we inadvertently remove
    a line segment when the path doubles back upon itself.
    
      Bug 26010 - cairo_line_to optimizes away path segments
      http://bugs.freedesktop.org/show_bug.cgi?id=26010
Comment 2 Alois 2010-01-12 14:35:23 UTC
Thanks for the very quick fix. I have backported the patch into my copy of 1.9.4 snapshot, it works fine now.


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