[ft-devel] important ftraster fix

[Werner LEMBERG]

David,


I'm going to apply the following patch below.  Without that change,
glyph `xi' in verdana.ttf at 13ppem has one pixel too much (see the
attached images).  I did a direct comparison with the rendering result
on Windows to find this particular problem.  BTW, two other glyphs in
tahoma.ttf, for example (one for Arabic and one for Thai), also
benefit from this change.  Images are attached, too.

However, glyph `afii57400' of tahoma.ttf is now rendered `better' than
on Windows.  It seems that we never can completely match the Windows
results :-( Reason is probably that the Windows rasterizer and
bytecode interpreter uses floating point arithmetic AFAIK.  Well...

Are the values I've selected for `step' and `jitter' reasonable?  Can
you give an explanation how the original values have been determined?

And finally: Do you see any problem with this change?  I could imagine
to introduce an `FT_OUTLINE_ULTRA_HIGH_PRECISION' for resolutions
lower than or equal to, say, 16ppem -- however, I think this is
probably unnecessary.


   Werner


======================================================================

--- ftraster.c.old      2009-06-07 08:20:54.000000000 +0200
+++ ftraster.c  2009-06-11 09:25:21.000000000 +0200
@@ -588,9 +588,9 @@
   {
     if ( High )
     {
-      ras.precision_bits   = 10;
-      ras.precision_step   = 128;
-      ras.precision_jitter = 24;
+      ras.precision_bits   = 12;
+      ras.precision_step   = 256;
+      ras.precision_jitter = 50;
     }
     else
     {