JDK-6449753 : Differences between Mustang rasterizer and MS Cleartype with subpixel AA
  • Type: Bug
  • Component: client-libs
  • Sub-Component: 2d
  • Affected Version: 6
  • Priority: P3
  • Status: Closed
  • Resolution: Other
  • OS: windows_xp
  • CPU: x86
  • Submitted: 2006-07-17
  • Updated: 2016-03-08
  • Resolved: 2016-03-08
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Description
A while ago I reported issues around the Mustang subpixel AA.
The differences between the Mustang rasterizer and MS Cleartype
are still significant for the Windows default control fonts with build 91.

There are two types of problems:
1) some Segoe UI glyphs look significantly different, e.g. 'e', 'a', 
 's', 'c', 't'
 
   changing the whole character and style of this great font. See
   http://www.jgoodies.com/vista/segoe-ui-comparison.png

2) The Mustang subpixel AA rasterizer doesn't scale the font weight
   (thickness of glyph lines) with the font size. Cleartype scales well,
   where Mustang seems to use integer metrics. Here's Cleartype:
      http://www.jgoodies.com/vista/segoe-ui-wordpad.png
   compared to Mustang:
      http://www.jgoodies.com/vista/segoe-ui-mustangb87.png

I would like to point developers and Sun folks to these issues.
And I couldn't find these issues in the bug database. I'm aware of
6438263 "Need to handle new TrueType 'gasp' table version in vista fonts",
4924220 (fixed) "Need to handle new TrueType 'gasp' table version in 
vista fonts",
and 6282527 "LCD text artifacts due to T2K (font rasteriser) scan 
conversion of contour to glyph image"
But none of them seems to describe the above types 1 and 2.

Comments
Not application anymore.
08-03-2016

EVALUATION This is another manifistation of our current approach to oversampling glyphs for subpixel rendering. At the moment we oversample hinted outline and as a result some rounding is performed on pixel instead of subpixel basis. Note that straightforward enabling hinting on scaled version of outline does not work well. For instance, some stems will be rounded to 1 "pixel in oversapled space" that will correspond to 1/3 or even 1/6 of actual pixel. As a result in such cases (e.g. courier) subpixel text will be extremely soft. However, in this particular case results of hinting on scaled outline are more similar to what MS does in terms of metrics. Disabling DELTA and CVT helps to improve quality and reduce number of sideeffects with such approach but result is still not ideal. This needs further investigation.
18-07-2006