diff options
Diffstat (limited to 'include/freetype/ftttdrv.h')
| -rw-r--r-- | include/freetype/ftttdrv.h | 71 |
1 files changed, 45 insertions, 26 deletions
diff --git a/include/freetype/ftttdrv.h b/include/freetype/ftttdrv.h index dc0081a..22186ee 100644 --- a/include/freetype/ftttdrv.h +++ b/include/freetype/ftttdrv.h @@ -5,7 +5,7 @@ /* FreeType API for controlling the TrueType driver */ /* (specification only). */ /* */ -/* Copyright 2013-2015 by */ +/* Copyright 2013-2016 by */ /* David Turner, Robert Wilhelm, and Werner Lemberg. */ /* */ /* This file is part of the FreeType project, and may only be used, */ @@ -17,8 +17,8 @@ /***************************************************************************/ -#ifndef __FTTTDRV_H__ -#define __FTTTDRV_H__ +#ifndef FTTTDRV_H_ +#define FTTTDRV_H_ #include <ft2build.h> #include FT_FREETYPE_H @@ -138,31 +138,37 @@ FT_BEGIN_HEADER * interpreter-version * * @description: - * Currently, two versions are available, representing the bytecode - * interpreter with and without subpixel hinting support, - * respectively. The default is subpixel support if - * TT_CONFIG_OPTION_SUBPIXEL_HINTING is defined, and no subpixel - * support otherwise (since it isn't available then). + + * Currently, three versions are available, two representing the + * bytecode interpreter with subpixel hinting support (old `Infinality' + * code and new stripped-down and higher performance `minimal' code) and + * one without, respectively. The default is subpixel support if + * TT_CONFIG_OPTION_SUBPIXEL_HINTING is defined, and no subpixel support + * otherwise (since it isn't available then). * * If subpixel hinting is on, many TrueType bytecode instructions behave * differently compared to B/W or grayscale rendering (except if `native - * ClearType' is selected by the font). The main idea is to render at a - * much increased horizontal resolution, then sampling down the created - * output to subpixel precision. However, many older fonts are not - * suited to this and must be specially taken care of by applying - * (hardcoded) font-specific tweaks. + * ClearType' is selected by the font). Microsoft's main idea is to + * render at a much increased horizontal resolution, then sampling down + * the created output to subpixel precision. However, many older fonts + * are not suited to this and must be specially taken care of by + * applying (hardcoded) tweaks in Microsoft's interpreter. * * Details on subpixel hinting and some of the necessary tweaks can be * found in Greg Hitchcock's whitepaper at - * `http://www.microsoft.com/typography/cleartype/truetypecleartype.aspx'. + * `http://www.microsoft.com/typography/cleartype/truetypecleartype.aspx'. + * Note that FreeType currently doesn't really `subpixel hint' (6x1, 6x2, + * or 6x5 supersampling) like discussed in the paper. Depending on the + * chosen interpreter, it simply ignores instructions on vertical stems + * to arrive at very similar results. * - * The following example code demonstrates how to activate subpixel + * The following example code demonstrates how to deactivate subpixel * hinting (omitting the error handling). * * { * FT_Library library; * FT_Face face; - * FT_UInt interpreter_version = TT_INTERPRETER_VERSION_38; + * FT_UInt interpreter_version = TT_INTERPRETER_VERSION_35; * * * FT_Init_FreeType( &library ); @@ -175,6 +181,8 @@ FT_BEGIN_HEADER * @note: * This property can be used with @FT_Property_Get also. * + * This property can be set via the `FREETYPE_PROPERTIES' environment + * variable (using values `35', `38', or `40'). */ @@ -197,9 +205,19 @@ FT_BEGIN_HEADER * * TT_INTERPRETER_VERSION_38 :: * Version~38 corresponds to MS rasterizer v.1.9; it is roughly - * equivalent to the hinting provided by DirectWrite ClearType (as - * can be found, for example, in the Internet Explorer~9 running on - * Windows~7). + * equivalent to the hinting provided by DirectWrite ClearType (as can + * be found, for example, in the Internet Explorer~9 running on + * Windows~7). It is used in FreeType to select the `Infinality' + * subpixel hinting code. The code may be removed in a future + * version. + * + * TT_INTERPRETER_VERSION_40 :: + * Version~40 corresponds to MS rasterizer v.2.1; it is roughly + * equivalent to the hinting provided by DirectWrite ClearType (as can + * be found, for example, in Microsoft's Edge Browser on Windows~10). + * It is used in FreeType to select the `minimal' subpixel hinting + * code, a stripped-down and higher performance version of the + * `Infinality' code. * * @note: * This property controls the behaviour of the bytecode interpreter @@ -207,9 +225,9 @@ FT_BEGIN_HEADER * get rasterized! In particular, it does not control subpixel color * filtering. * - * If FreeType has not been compiled with configuration option - * FT_CONFIG_OPTION_SUBPIXEL_HINTING, selecting version~38 causes an - * `FT_Err_Unimplemented_Feature' error. + * If FreeType has not been compiled with the configuration option + * FT_CONFIG_OPTION_SUBPIXEL_HINTING, selecting version~38 or~40 causes + * an `FT_Err_Unimplemented_Feature' error. * * Depending on the graphics framework, Microsoft uses different * bytecode and rendering engines. As a consequence, the version @@ -290,13 +308,14 @@ FT_BEGIN_HEADER * the version~1 gasp table exclusively (like Color ClearType), while * v1.6 only respects the values of version~0 (bits 0 and~1). * - * FreeType doesn't provide all capabilities of the most recent - * ClearType incarnation, thus we identify our subpixel support as - * version~38. + * Keep in mind that the features of the above interpreter versions + * might not map exactly to FreeType features or behavior because it is + * a fundamentally different library with different internals. * */ #define TT_INTERPRETER_VERSION_35 35 #define TT_INTERPRETER_VERSION_38 38 +#define TT_INTERPRETER_VERSION_40 40 /* */ @@ -304,7 +323,7 @@ FT_BEGIN_HEADER FT_END_HEADER -#endif /* __FTTTDRV_H__ */ +#endif /* FTTTDRV_H_ */ /* END */ |