From a6feefdfefd6eb8e62728f40638241bb1d8c993e Mon Sep 17 00:00:00 2001 From: Nikolaus Waxweiler Date: Sat, 2 Feb 2019 15:50:57 +0000 Subject: [PATCH] [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. --- ChangeLog | 11 ++++++++ src/truetype/ttgxvar.c | 62 +++++++++++++++++++++++++++++------------- 2 files changed, 54 insertions(+), 19 deletions(-) diff --git a/ChangeLog b/ChangeLog index aac45a472..870972c83 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,14 @@ +2019-02-02 Nikolaus Waxweiler + + [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 [sfnt] Use typo metrics if OS/2 fsSelection USE_TYPO_METRICS bit is set. diff --git a/src/truetype/ttgxvar.c b/src/truetype/ttgxvar.c index a2e6dd137..787d68614 100644 --- a/src/truetype/ttgxvar.c +++ b/src/truetype/ttgxvar.c @@ -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;