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[sfnt, truetype] Improve handling of missing sbits.

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Requested by Behdad.

Modern bitmap-only SFNTs like `NotoColorEmoji.ttf' don't contain
entries in the bitmap strike(s) for empty glyphs.  Instead, they
rely that a space glyph gets created from the font's metrics data.
This commit makes FreeType behave accordingly.

* include/freetype/fterrdef.h (FT_Err_Missing_Bitmap): New error
code.

* src/sfnt/ttsbit.c (tt_sbit_decoder_load_image): Change error codes
to make a distinction between a missing bitmap in a composite and a
simple missing bitmap.

* src/truetype/ttgload.c (TT_Load_Glyph): For a missing bitmap (in a
bitmap-only font), synthesize an empty bitmap glyph if metrics are
available.
This commit is contained in:
Werner Lemberg 2017-08-11 09:34:20 +02:00
parent e77ee789fa
commit b45043c440
4 changed files with 86 additions and 4 deletions
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22
ChangeLog
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@ -1,3 +1,25 @@
2017-08-11 Werner Lemberg <wl@gnu.org>
[sfnt, truetype] Improve handling of missing sbits.
Requested by Behdad.
Modern bitmap-only SFNTs like `NotoColorEmoji.ttf' don't contain
entries in the bitmap strike(s) for empty glyphs. Instead, they
rely that a space glyph gets created from the font's metrics data.
This commit makes FreeType behave accordingly.
* include/freetype/fterrdef.h (FT_Err_Missing_Bitmap): New error
code.
* src/sfnt/ttsbit.c (tt_sbit_decoder_load_image): Change error codes
to make a distinction between a missing bitmap in a composite and a
simple missing bitmap.
* src/truetype/ttgload.c (TT_Load_Glyph): For a missing bitmap (in a
bitmap-only font), synthesize an empty bitmap glyph if metrics are
available.
2017-08-10 Werner Lemberg <wl@gnu.org>
[base] Minor API improvement for default variation axis setting.

2
include/freetype/fterrdef.h
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@ -233,6 +233,8 @@
"invalid PostScript (post) table" )
FT_ERRORDEF_( DEF_In_Glyf_Bytecode, 0x9C,
"found FDEF or IDEF opcode in glyf bytecode" )
FT_ERRORDEF_( Missing_Bitmap, 0x9D,
"missing bitmap in strike" )
/* CFF, CID, and Type 1 errors */

11
src/sfnt/ttsbit.c
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@ -1448,10 +1448,17 @@
return FT_THROW( Invalid_Table );
NoBitmap:
if ( recurse_count )
{
FT_TRACE4(( "tt_sbit_decoder_load_image:"
" missing subglyph sbit with glyph index %d\n",
glyph_index ));
return FT_THROW( Invalid_Composite );
}
FT_TRACE4(( "tt_sbit_decoder_load_image:"
" no sbit found for glyph index %d\n", glyph_index ));
return FT_THROW( Invalid_Argument );
return FT_THROW( Missing_Bitmap );
}

55
src/truetype/ttgload.c
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@ -87,7 +87,7 @@
/*************************************************************************/
/* */
/* Return the vertical metrics in font units for a given glyph. */
/* See macro `TT_LOADER_SET_PP' below for explanations. */
/* See function `tt_loader_set_pp' below for explanations. */
/* */
FT_LOCAL_DEF( void )
TT_Get_VMetrics( TT_Face face,
@ -2625,7 +2625,58 @@
IS_DEFAULT_INSTANCE )
{
error = load_sbit_image( size, glyph, glyph_index, load_flags );
if ( error )
if ( FT_ERR_EQ( error, Missing_Bitmap ) )
{
/* the bitmap strike is incomplete and misses the requested glyph; */
/* if we have a bitmap-only font, return an empty glyph */
if ( !FT_IS_SCALABLE( glyph->face ) )
{
TT_Face face = (TT_Face)glyph->face;
FT_Short left_bearing = 0, top_bearing = 0;
FT_UShort advance_width = 0, advance_height = 0;
/* to return an empty glyph, however, we need metrics data */
/* from the `hmtx' (or `vmtx') table; the assumption is that */
/* empty glyphs are missing intentionally, representing */
/* whitespace - not having at least horizontal metrics is */
/* thus considered an error */
if ( !face->horz_metrics_size )
return error;
/* we now construct an empty bitmap glyph */
TT_Get_HMetrics( face, glyph_index,
&left_bearing,
&advance_width );
TT_Get_VMetrics( face, glyph_index,
0,
&top_bearing,
&advance_height );
glyph->outline.n_points = 0;
glyph->outline.n_contours = 0;
glyph->metrics.width = 0;
glyph->metrics.height = 0;
glyph->metrics.horiBearingX = left_bearing;
glyph->metrics.horiBearingY = 0;
glyph->metrics.horiAdvance = advance_width;
glyph->metrics.vertBearingX = 0;
glyph->metrics.vertBearingY = top_bearing;
glyph->metrics.vertAdvance = advance_height;
glyph->format = FT_GLYPH_FORMAT_BITMAP;
glyph->bitmap.pixel_mode = FT_PIXEL_MODE_MONO;
glyph->bitmap_left = 0;
glyph->bitmap_top = 0;
return FT_Err_Ok;
}
}
else if ( error )
{
/* return error if font is not scalable */
if ( !FT_IS_SCALABLE( glyph->face ) )