[cairo-bugs] [Bug 23333] New: Mismatches hinting at certain glyph pixelsizes.

[bugzilla-daemon at freedesktop.org]

http://bugs.freedesktop.org/show_bug.cgi?id=23333

           Summary: Mismatches hinting at certain glyph pixelsizes.
           Product: cairo
           Version: 1.8.8
          Platform: x86 (IA32)
        OS/Version: Linux (All)
            Status: NEW
          Severity: minor
          Priority: low
         Component: general
        AssignedTo: cworth at cworth.org
        ReportedBy: craftjml+freedesktopbugs at gmail.com
         QAContact: cairo-bugs at cairographics.org


Fedora 11, Cairo 1.8.8, GTK 2.16.5.

When jumping between certain increments of pixelsize, GTK/Cairo appears to
render the wrong size font when hinting is enabled.

(This does not appear when hinting is disabled).

How to Duplicate:
1.  Go to GNOME Appearance\Font properties.
2.  Under Details, set 72 DPI (makes fontsize corresponds to fontconfig's
pixelsize).
3.  Back at the font tab, open both a) a font selection dialog (for Application
font) and b) the Details box from the Font tab.
4.  Examine DejaVu Sans, Book, size 12.5.
5.  On the open Details dialog, switch between None and
Slight/Medium/Whichever-you-like hinting.
6.  Notice how the font glyph is rendered at a small size when hinting is
turned on.

(Note that unhinted pixel sizes 12.0-12.49 appear nearly identical.  They show
minor variations in size when hinted.  But a hinted pixelsize 12.5 glyph is
actually -smaller- than its unhinted version).

It clearly does not make sense that size 12.5 becomes -smaller- when hinting is
disabled.

(This problem occurs with any font, from pixelsize 12.5 to pixelsize 13.1, and
again within pixelsizes 14.5-14.99.  It may also occur in other pixelsizes I
have not checked.)

[Font-screen-grabs were taken using GNOME's Appearance\Fonts dialog, with DPI
72 (at which font size corresponds to fontconfig's pixelsize scale), and then
assembled in the GIMP].

I was unsure if this was a bug in GTK, cairo, or freetype.  But according to my
layman guess, freetype merely generates glyphs, GTK uses cairo to draw, and
cairo uses freetype (I believe), so cairo it is.  No idea what specific
component of cairo though.


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