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[Devel] TrueType monochrome rendering quality improved

From: David Turner
Subject: [Devel] TrueType monochrome rendering quality improved
Date: Tue, 26 Mar 2002 19:33:37 +0100


  I have spent the last few days investigating the reasons why
  FT1 and FT2 do sometimes produce different monochrome glyphs
  when the bytecode interpreter is enabled in both libraries..

  Fact was that the computation routines were slightly different,
  and that TT bytecode interpretation seems to be _extremely_
  sensitive to rounding errors when performing dot products and
  fixed-point square roots.

  As a consequence, I have included all required computation
  routines, (along with some optimisations :o) within "ttinterp.c"
  to ensure that everything runs well in all cases.. I also got
  rid of the obsolete FT_CONFIG_OPTION_OLD_CALCS macros and
  associated code in "ftcalc.c"

  The output of FT2 is now much better, though there are still
  very subtle differences with FT1 with _very_ rare glyphs. This
  is probably due to slight differences within the scanline
  rasterizers and will be studied later..

  On the other hand, there is strictly _no_ noticeable difference
  when it comes to anti-aliased text between 2.0.9 and the current
  CVS sources..


- David Turner

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