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[truetype] Apply MVAR hasc, hdsc and hlgp metrics to current FT_Face metrics. 

Instead of setting typo or win metrics as the new FT_Face metrics
indiscriminately, apply only typo deltas to the currently active FT_Face
metrics. This prevents line height differences when e.g. the default
outlines were used as the regular face and instances for everything else.

* src/truetype/ttgxvar.c (tt_apply_mvar): Implement.
This commit is contained in:
Nikolaus Waxweiler 2019-02-02 15:50:57 +00:00
parent f72b00746c
commit a6feefdfef
2 changed files with 54 additions and 19 deletions
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11
ChangeLog
View File

@ -1,3 +1,14 @@
2019-02-02 Nikolaus Waxweiler <madigens@gmail.com>
[truetype] Apply MVAR hasc, hdsc and hlgp metrics to current FT_Face metrics.
Instead of setting typo or win metrics as the new FT_Face metrics
indiscriminately, apply only typo deltas to the currently active FT_Face
metrics. This prevents line height differences when e.g. the default
outlines were used as the regular face and instances for everything else.
* src/truetype/ttgxvar.c (tt_apply_mvar): Implement.
2019-02-02 Nikolaus Waxweiler <madigens@gmail.com>
[sfnt] Use typo metrics if OS/2 fsSelection USE_TYPO_METRICS bit is set.

62
src/truetype/ttgxvar.c
View File

@ -1325,6 +1325,9 @@
{
GX_Blend blend = face->blend;
GX_Value value, limit;
FT_Short mvar_hasc_delta = 0;
FT_Short mvar_hdsc_delta = 0;
FT_Short mvar_hlgp_delta = 0;
if ( !( face->variation_support & TT_FACE_FLAG_VAR_MVAR ) )
@ -1359,6 +1362,14 @@
/* since we handle both signed and unsigned values as FT_Short, */
/* ensure proper overflow arithmetic */
*p = (FT_Short)( value->unmodified + (FT_Short)delta );
/* Treat hasc, hdsc and hlgp specially, see below. */
if ( value->tag == MVAR_TAG_HASC )
mvar_hasc_delta = (FT_Short)delta;
else if ( value->tag == MVAR_TAG_HDSC )
mvar_hdsc_delta = (FT_Short)delta;
else if ( value->tag == MVAR_TAG_HLGP )
mvar_hlgp_delta = (FT_Short)delta;
}
}
@ -1366,25 +1377,38 @@
{
FT_Face root = &face->root;
if ( face->os2.version != 0xFFFFU )
{
if ( face->os2.sTypoAscender || face->os2.sTypoDescender )
{
root->ascender = face->os2.sTypoAscender;
root->descender = face->os2.sTypoDescender;
root->height = root->ascender - root->descender +
face->os2.sTypoLineGap;
}
else
{
root->ascender = (FT_Short)face->os2.usWinAscent;
root->descender = -(FT_Short)face->os2.usWinDescent;
root->height = root->ascender - root->descender;
}
}
/*
* Apply the deltas of hasc, hdsc and hlgp to the FT_Face's ascender,
* descender and height attributes, no matter how they were originally
* computed.
*
* (Code that ignores those and accesses the font's metrics values
* directly is already served by the delta application code above.)
*
* The MVAR table supports variations for both typo and win metrics.
* According to Behdad Esfahbod, the thinking of the working group was
* that no one uses win metrics anymore for setting line metrics (the
* specification even calls these metrics "horizontal clipping
* ascent/descent", probably for their role on the Windows platform in
* computing clipping boxes), and new fonts should use typo metrics, so
* typo deltas should be applied to whatever sfnt_load_face decided the
* line metrics should be.
*
* Before, the following led to different line metrics between default
* outline and instances, visible when e.g. the default outlines were
* used as the regular face and instances for everything else:
*
* 1. sfnt_load_face applied the hhea metrics by default.
* 2. This code later applied the typo metrics by default, regardless of
* whether they were actually changed or the font had the OS/2 table's
* fsSelection's bit 7 (USE_TYPO_METRICS) set.
*/
FT_Short current_line_gap = root->height - root->ascender +
root->descender;
root->ascender = root->ascender + mvar_hasc_delta;
root->descender = root->descender + mvar_hdsc_delta;
root->height = root->ascender - root->descender +
current_line_gap + mvar_hlgp_delta;
root->underline_position = face->postscript.underlinePosition -
face->postscript.underlineThickness / 2;