Commit 1036409692909705332be4f2b0181c2d250496dc
2012-03-11T15:20:32
[autofit] Return correct linear advance width values. This was quite a subtle bug which accidentally showed up with glyph `afii10023' of arial.ttf (version 2.76). This glyph is a composite; the first component, `E', has an advance width of 1366 font units, while the advance width of the composite itself (which looks like uppercase `E' with dieresis) is 1367 font units. I think this is actually a bug in the font itself, because there is no reason that this glyph has not the same width as uppercase `E' without the dieresis. Anyway, it helped identify this problem. Using the TrueType hinter, the correct value (1367) of `afii10023' was returned, but the autohinter mysteriously returned 1366. Digging in the code showed that the autohinter recursively calls FT_Load_Glyph to load the glyph, adding the FT_LOAD_NO_SCALE load flag. However, the `linearHoriAdvance' field is still returned as a scaled value. To avoid scaling twice, the old code in autofit reset `linearHoriAdvance', using the `horiAdvance' field. This seemed to work since FT_LOAD_NO_SCALE was in use, but it failed actually, because `horiAdvance' is defined as the distance of the first subglyph's phantom points, which in turn are initialized using the advance width of the first subglyph. And as the given example shows, these widths can differ. * src/autofit/afloader.c (af_loader_load_g): Temporarily set FT_LOAD_LINEAR_DESIGN while calling FT_Load_Glyph to get unscaled values for the linear advance widths.
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diff --git a/ChangeLog b/ChangeLog
index a34f8e8..69b22bc 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,34 @@
+2012-03-11 Werner Lemberg <wl@gnu.org>
+
+ [autofit] Return correct linear advance width values.
+
+ This was quite a subtle bug which accidentally showed up with glyph
+ `afii10023' of arial.ttf (version 2.76). This glyph is a composite;
+ the first component, `E', has an advance width of 1366 font units,
+ while the advance width of the composite itself (which looks like
+ uppercase `E' with dieresis) is 1367 font units. I think this is
+ actually a bug in the font itself, because there is no reason that
+ this glyph has not the same width as uppercase `E' without the
+ dieresis. Anyway, it helped identify this problem.
+
+ Using the TrueType hinter, the correct value (1367) of `afii10023'
+ was returned, but the autohinter mysteriously returned 1366.
+
+ Digging in the code showed that the autohinter recursively calls
+ FT_Load_Glyph to load the glyph, adding the FT_LOAD_NO_SCALE load
+ flag. However, the `linearHoriAdvance' field is still returned as a
+ scaled value. To avoid scaling twice, the old code in autofit reset
+ `linearHoriAdvance', using the `horiAdvance' field. This seemed to
+ work since FT_LOAD_NO_SCALE was in use, but it failed actually,
+ because `horiAdvance' is defined as the distance of the first
+ subglyph's phantom points, which in turn are initialized using the
+ advance width of the first subglyph. And as the given example
+ shows, these widths can differ.
+
+ * src/autofit/afloader.c (af_loader_load_g): Temporarily set
+ FT_LOAD_LINEAR_DESIGN while calling FT_Load_Glyph to get unscaled
+ values for the linear advance widths.
+
2012-03-10 Werner Lemberg <wl@gnu.org>
[truetype] Fix SSW instruction.
diff --git a/src/autofit/afloader.c b/src/autofit/afloader.c
index 34ef9d8..dabd619 100644
--- a/src/autofit/afloader.c
+++ b/src/autofit/afloader.c
@@ -104,9 +104,11 @@
AF_GlyphHints hints = &loader->hints;
FT_GlyphSlot slot = face->glyph;
FT_Slot_Internal internal = slot->internal;
+ FT_Int32 flags;
- error = FT_Load_Glyph( face, glyph_index, load_flags );
+ flags = load_flags | FT_LOAD_LINEAR_DESIGN;
+ error = FT_Load_Glyph( face, glyph_index, flags );
if ( error )
goto Exit;
@@ -124,10 +126,6 @@
FT_Vector_Transform( &loader->trans_delta, &inverse );
}
- /* set linear metrics */
- slot->linearHoriAdvance = slot->metrics.horiAdvance;
- slot->linearVertAdvance = slot->metrics.vertAdvance;
-
switch ( slot->format )
{
case FT_GLYPH_FORMAT_OUTLINE: