Hello everyone,
just to let you know that I just introduced in the CVS depot a new API (and corresponding header)
to be able to more quickly retrieve the advance width of individual glyphs without loading their
outlines.
the new header file if FT_ADVANCES_H (a.k.a. freetype/ftadvanc.h) and provides two new APIs
(see copy of the header file with docs below).
the 'ftbench' demo program has also been updated with a new test that exercise the new APIs
in both "normal" and "fast" mode (see below).
this works as follows:
when using a strongly hinted mode (either auto-hinted or bytecoded), this does perform the hinting
and retrieves the advance(s) after that. this is slightly faster (about 10-20%) than doing successive
FT_Load_Glyph() calls, depending on the font backend being used.
however, when using no scaling, no hinting or even the "light hinting mode" (which only hints in the
vertical dimension), the function can return results *immediately* simply looking the values in the font
file itself, if the font driver supports it. I have added support for this in the TrueType / Type1 and CFF
font drivers. I still need to add CID and PFR support (I really don't think Type42 is needed)
here are some runs of the new 'ftbench' on one of my work machines:
$ objs/ftbench /usr/share/fonts/truetype/ttf-dejavu/DejaVuSerif.ttf
Load : 19.415 us/op
Load_Advances (Normal) : 16.327 us/op
Load_Advances (Fast) : 0.034 us/op
Render : 6.285 us/op
Get_Glyph : 1.077 us/op
Get_CBox : 0.539 us/op
Get_Char_Index : 0.074 us/op
Iterate CMap : 35.950 us/op
New_Face : 100.482 us/op
Embolden : 0.000 us/op
$ objs/ftbench /usr/share/fonts/type1/t1-xfree86-nonfree/cour.pfa
Load : 21.810 us/op
Load_Advances (Normal) : 13.508 us/op
Load_Advances (Fast) : 0.080 us/op
Render : 8.756 us/op
Get_Glyph : 1.190 us/op
Get_CBox : 0.118 us/op
Get_Char_Index : 0.057 us/op
Iterate CMap : 31.968 us/op
New_Face : 1855.956 us/op
Embolden : 0.222 us/op
feel free to comment on the API and suggest improvements if you see any problem here.
Regards,
- David
copy of the new header file below:
/*************************************************************************/
/* */ /* <Const> */
/* FT_ADVANCE_FLAG_FAST_ONLY */ /* */
/* <Description> */ /* a bit-flag to be or-ed to the 'flags' parameter of the */
/* @FT_Get_Advance and @FT_Get_Advances. */ /* */
/* when set, it indicates that you want these functions to fail */ /* if the corresponding hinting mode or font driver doesn't */
/* allow for very quick advance computation. */ /* */
/* typically, unscaled, unhinted, bitmapped and light-hinted glyphs */ /* can have their advance width(s) computed very quickly. */
/* */ /* not so for normal and bytecode hinted modes, which require */
/* loading/scaling/hinting the glyph outline instead, which is */ /* extremely slow by comparison */
/* */#define FT_ADVANCE_FLAG_FAST_ONLY 0x20000000U
/*************************************************************************/
/* */ /* <Function> */
/* FT_Get_Advance */ /* */
/* <Description> */ /* Retrieve the advance of a given glyph outline in a @FT_Face. */
/* by default, the unhinted advance is returned in font units */ /* */
/* <Input> */ /* face :: source @FT_Face handle */
/* gindex :: glyph index */ /* load_flags :: a set of bit-flags similar to those used */
/* when calling @FT_Load_Glyph, used to determine */ /* what kind of advances you need. */
/* <Output> */ /* padvance :: the advance value, in either font units or 16.16 */
/* format. */ /* */
/* if @FT_LOAD_VERTICAL_LAYOUT is set, this is the */ /* vertical advance corresponding to a vertical layout. */
/* otherwise, it's the horizontal advance in an */ /* horizontal layout. */
/* <Return> */ /* FreeType error code. 0 means success. */
/* */ /* <Note> */
/* This function may fail if you use @FT_ADVANCE_FLAG_FAST_ONLY and */ /* if the corresponding's font backend doesn't have a quick way to */
/* retrieve the advances. */ /* */
/* A scaled advance is returned in 16.16 format, but isn't */ /* transformed by the affine transform specified by @FT_Set_Transform */
/* */ FT_EXPORT( FT_Error )
FT_Get_Advance( FT_Face face, FT_UInt gindex,
FT_UInt load_flags, FT_Fixed *padvance );
/*************************************************************************/
/* */ /* <Function> */
/* FT_Get_Advances */ /* */
/* <Description> */ /* Retrieve the advance of several glyph outlines in a @FT_Face. */
/* by default, the unhinted advances are returned in font units */ /* */
/* <Input> */ /* face :: source @FT_Face handle */
/* start :: first glyph index */ /* count :: number of advances you want to retrieve */
/* load_flags :: a set of bit-flags similar to those used when */ /* calling @FT_Load_Glyph. */
/* */ /* <Output> */
/* padvance :: the advances, in either font units or 16.16 format. */ /* this array must contain at least 'count' elements */
/* */ /* if @FT_LOAD_VERTICAL_LAYOUT is set, these are the */
/* vertical advances corresponding to a vertical layout. */ /* otherwise, they are the horizontal advances in an */
/* horizontal layout. */ /* <Return> */
/* FreeType error code. 0 means success. */ /* */
/* <Note> */ /* This function may fail if you use @FT_ADVANCE_FLAG_FAST_ONLY and */
/* if the corresponding's font backend doesn't have a quick way to */ /* retrieve the advances. */
/* */ /* Scaled advances are returned in 16.16 format, but aren't */
/* transformed by the affine transform specified by @FT_Set_Transform */ /* */
FT_EXPORT( FT_Error ) FT_Get_Advances( FT_Face face,
FT_UInt start, FT_UInt count,
FT_UInt load_flags, FT_Fixed *padvances );