diff options
Diffstat (limited to 'include/ftttdrv.h')
| -rw-r--r-- | include/ftttdrv.h | 109 |
1 files changed, 86 insertions, 23 deletions
diff --git a/include/ftttdrv.h b/include/ftttdrv.h index 70ad3d5..f56040b 100644 --- a/include/ftttdrv.h +++ b/include/ftttdrv.h @@ -5,7 +5,7 @@ /* FreeType API for controlling the TrueType driver */ /* (specification only). */ /* */ -/* Copyright 2013 by */ +/* Copyright 2013-2015 by */ /* David Turner, Robert Wilhelm, and Werner Lemberg. */ /* */ /* This file is part of the FreeType project, and may only be used, */ @@ -67,13 +67,13 @@ FT_BEGIN_HEADER * 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. 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. + * 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. * * Details on subpixel hinting and some of the necessary tweaks can be * found in Greg Hitchcock's whitepaper at @@ -135,32 +135,95 @@ FT_BEGIN_HEADER * `FT_Err_Unimplemented_Feature' error. * * Depending on the graphics framework, Microsoft uses different - * bytecode engines. As a consequence, the version numbers returned by - * a call to the `GETINFO[1]' bytecode instruction are more convoluted - * than desired. + * bytecode and rendering engines. As a consequence, the version + * numbers returned by a call to the `GETINFO' bytecode instruction are + * more convoluted than desired. + * + * Here are two tables that try to shed some light on the possible + * values for the MS rasterizer engine, together with the additional + * features introduced by it. * * { - * framework Windows version result of GETINFO[1] - * ---------------------------------------------------- - * GDI before XP 35 - * GDI XP and later 37 - * GDI+ old before Vista 37 - * GDI+ old Vista, 7 38 - * GDI+ after 7 40 - * DWrite before 8 39 - * DWrite 8 and later 40 + * GETINFO framework version feature + * ------------------------------------------------------------------- + * 3 GDI (Win 3.1), v1.0 16-bit, first version + * TrueImage + * 33 GDI (Win NT 3.1), v1.5 32-bit + * HP Laserjet + * 34 GDI (Win 95) v1.6 font smoothing, + * new SCANTYPE opcode + * 35 GDI (Win 98/2000) v1.7 (UN)SCALED_COMPONENT_OFFSET + * bits in composite glyphs + * 36 MGDI (Win CE 2) v1.6+ classic ClearType + * 37 GDI (XP and later), v1.8 ClearType + * GDI+ old (before Vista) + * 38 GDI+ old (Vista, Win 7), v1.9 subpixel ClearType, + * WPF Y-direction ClearType, + * additional error checking + * 39 DWrite (before Win 8) v2.0 subpixel ClearType flags + * in GETINFO opcode, + * bug fixes + * 40 GDI+ (after Win 7), v2.1 Y-direction ClearType flag + * DWrite (Win 8) in GETINFO opcode, + * Gray ClearType * } * - * Since FreeType doesn't provide all capabilities of DWrite ClearType, - * using version~38 seems justified. + * The `version' field gives a rough orientation only, since some + * applications provided certain features much earlier (as an example, + * Microsoft Reader used subpixel and Y-direction ClearType already in + * Windows 2000). Similarly, updates to a given framework might include + * improved hinting support. + * + * { + * version sampling rendering comment + * x y x y + * -------------------------------------------------------------- + * v1.0 normal normal B/W B/W bi-level + * v1.6 high high gray gray grayscale + * v1.8 high normal color-filter B/W (GDI) ClearType + * v1.9 high high color-filter gray Color ClearType + * v2.1 high normal gray B/W Gray ClearType + * v2.1 high high gray gray Gray ClearType + * } + * + * Color and Gray ClearType are the two available variants of + * `Y-direction ClearType', meaning grayscale rasterization along the + * Y-direction; the name used in the TrueType specification for this + * feature is `symmetric smoothing'. `Classic ClearType' is the + * original algorithm used before introducing a modified version in + * Win~XP. Another name for v1.6's grayscale rendering is `font + * smoothing', and `Color ClearType' is sometimes also called `DWrite + * ClearType'. To differentiate between today's Color ClearType and the + * earlier ClearType variant with B/W rendering along the vertical axis, + * the latter is sometimes called `GDI ClearType'. + * + * `Normal' and `high' sampling describe the (virtual) resolution to + * access the rasterized outline after the hinting process. `Normal' + * means 1 sample per grid line (i.e., B/W). In the current Microsoft + * implementation, `high' means an extra virtual resolution of 16x16 (or + * 16x1) grid lines per pixel for bytecode instructions like `MIRP'. + * After hinting, these 16 grid lines are mapped to 6x5 (or 6x1) grid + * lines for color filtering if Color ClearType is activated. + * + * Note that `Gray ClearType' is essentially the same as v1.6's + * grayscale rendering. However, the GETINFO instruction handles it + * differently: v1.6 returns bit~12 (hinting for grayscale), while v2.1 + * returns bits~13 (hinting for ClearType), 18 (symmetrical smoothing), + * and~19 (Gray ClearType). Also, this mode respects bits 2 and~3 for + * 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. * */ #define TT_INTERPRETER_VERSION_35 35 #define TT_INTERPRETER_VERSION_38 38 - /* */ + FT_END_HEADER |