[cairo-bugs] [Bug 28583] New: PDF glyph_path() inaccuracies

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=28583

           Summary: PDF glyph_path() inaccuracies
           Product: cairo
           Version: 1.8.6
          Platform: x86-64 (AMD64)
        OS/Version: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: pdf backend
        AssignedTo: ajohnson at redneon.com
        ReportedBy: britten at caris.com
         QAContact: cairo-bugs at cairographics.org


Created an attachment (id=36336)
 --> (https://bugs.freedesktop.org/attachment.cgi?id=36336)
Sample C program that reproduces the glyph_path() PDF problem

There appears to be some inaccuracies from cairo_glyph_path(), when written to
PDF.  Note the problem may only be noticeable when the text is tiny/small
(which is the case I encountered).

Use cairo_glyph_path() to convert a glyph to a path, then stroke() it with a
thick lineweight.  Then, do a show_glyphs() directly after (Different colour,
but same position/size/etc).  In the resulting PDF, the 'halo' outline isn't
evenly aligned around the text, as would be expected.  However, rendering the
same data to an image surface produces the expected output.

Attached is a stand-alone test program that demonstrates the problem.  The
single glyph is rendered at the centre of the output files.
[ WARNING - It produces a *huge* PNG for comparison, in addition to the PDF. 
Disable the PNG if desired ]

This has already been investigated some by Chris Wilson (ickle) on IRC.  He has
triaged the problem some, and says: "... mention that I think it is due to the
Tm matrix".  He also suggested CC'ing Adrian

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