1 /**************************************************************************** 2 * 3 * ftdriver.h 4 * 5 * FreeType API for controlling driver modules (specification only). 6 * 7 * Copyright (C) 2017-2021 by 8 * David Turner, Robert Wilhelm, and Werner Lemberg. 9 * 10 * This file is part of the FreeType project, and may only be used, 11 * modified, and distributed under the terms of the FreeType project 12 * license, LICENSE.TXT. By continuing to use, modify, or distribute 13 * this file you indicate that you have read the license and 14 * understand and accept it fully. 15 * 16 */ 17 18 19 #ifndef FTDRIVER_H_ 20 #define FTDRIVER_H_ 21 22 #include <freetype/freetype.h> 23 #include <freetype/ftparams.h> 24 25 #ifdef FREETYPE_H 26 #error "freetype.h of FreeType 1 has been loaded!" 27 #error "Please fix the directory search order for header files" 28 #error "so that freetype.h of FreeType 2 is found first." 29 #endif 30 31 32 FT_BEGIN_HEADER 33 34 35 /************************************************************************** 36 * 37 * @section: 38 * auto_hinter 39 * 40 * @title: 41 * The auto-hinter 42 * 43 * @abstract: 44 * Controlling the auto-hinting module. 45 * 46 * @description: 47 * While FreeType's auto-hinter doesn't expose API functions by itself, 48 * it is possible to control its behaviour with @FT_Property_Set and 49 * @FT_Property_Get. The following lists the available properties 50 * together with the necessary macros and structures. 51 * 52 * Note that the auto-hinter's module name is 'autofitter' for historical 53 * reasons. 54 * 55 * Available properties are @increase-x-height, @no-stem-darkening 56 * (experimental), @darkening-parameters (experimental), 57 * @glyph-to-script-map (experimental), @fallback-script (experimental), 58 * and @default-script (experimental), as documented in the @properties 59 * section. 60 * 61 */ 62 63 64 /************************************************************************** 65 * 66 * @section: 67 * cff_driver 68 * 69 * @title: 70 * The CFF driver 71 * 72 * @abstract: 73 * Controlling the CFF driver module. 74 * 75 * @description: 76 * While FreeType's CFF driver doesn't expose API functions by itself, it 77 * is possible to control its behaviour with @FT_Property_Set and 78 * @FT_Property_Get. 79 * 80 * The CFF driver's module name is 'cff'. 81 * 82 * Available properties are @hinting-engine, @no-stem-darkening, 83 * @darkening-parameters, and @random-seed, as documented in the 84 * @properties section. 85 * 86 * 87 * **Hinting and anti-aliasing principles of the new engine** 88 * 89 * The rasterizer is positioning horizontal features (e.g., ascender 90 * height & x-height, or crossbars) on the pixel grid and minimizing the 91 * amount of anti-aliasing applied to them, while placing vertical 92 * features (vertical stems) on the pixel grid without hinting, thus 93 * representing the stem position and weight accurately. Sometimes the 94 * vertical stems may be only partially black. In this context, 95 * 'anti-aliasing' means that stems are not positioned exactly on pixel 96 * borders, causing a fuzzy appearance. 97 * 98 * There are two principles behind this approach. 99 * 100 * 1) No hinting in the horizontal direction: Unlike 'superhinted' 101 * TrueType, which changes glyph widths to accommodate regular 102 * inter-glyph spacing, Adobe's approach is 'faithful to the design' in 103 * representing both the glyph width and the inter-glyph spacing designed 104 * for the font. This makes the screen display as close as it can be to 105 * the result one would get with infinite resolution, while preserving 106 * what is considered the key characteristics of each glyph. Note that 107 * the distances between unhinted and grid-fitted positions at small 108 * sizes are comparable to kerning values and thus would be noticeable 109 * (and distracting) while reading if hinting were applied. 110 * 111 * One of the reasons to not hint horizontally is anti-aliasing for LCD 112 * screens: The pixel geometry of modern displays supplies three vertical 113 * subpixels as the eye moves horizontally across each visible pixel. On 114 * devices where we can be certain this characteristic is present a 115 * rasterizer can take advantage of the subpixels to add increments of 116 * weight. In Western writing systems this turns out to be the more 117 * critical direction anyway; the weights and spacing of vertical stems 118 * (see above) are central to Armenian, Cyrillic, Greek, and Latin type 119 * designs. Even when the rasterizer uses greyscale anti-aliasing instead 120 * of color (a necessary compromise when one doesn't know the screen 121 * characteristics), the unhinted vertical features preserve the design's 122 * weight and spacing much better than aliased type would. 123 * 124 * 2) Alignment in the vertical direction: Weights and spacing along the 125 * y~axis are less critical; what is much more important is the visual 126 * alignment of related features (like cap-height and x-height). The 127 * sense of alignment for these is enhanced by the sharpness of grid-fit 128 * edges, while the cruder vertical resolution (full pixels instead of 129 * 1/3 pixels) is less of a problem. 130 * 131 * On the technical side, horizontal alignment zones for ascender, 132 * x-height, and other important height values (traditionally called 133 * 'blue zones') as defined in the font are positioned independently, 134 * each being rounded to the nearest pixel edge, taking care of overshoot 135 * suppression at small sizes, stem darkening, and scaling. 136 * 137 * Hstems (this is, hint values defined in the font to help align 138 * horizontal features) that fall within a blue zone are said to be 139 * 'captured' and are aligned to that zone. Uncaptured stems are moved 140 * in one of four ways, top edge up or down, bottom edge up or down. 141 * Unless there are conflicting hstems, the smallest movement is taken to 142 * minimize distortion. 143 * 144 */ 145 146 147 /************************************************************************** 148 * 149 * @section: 150 * pcf_driver 151 * 152 * @title: 153 * The PCF driver 154 * 155 * @abstract: 156 * Controlling the PCF driver module. 157 * 158 * @description: 159 * While FreeType's PCF driver doesn't expose API functions by itself, it 160 * is possible to control its behaviour with @FT_Property_Set and 161 * @FT_Property_Get. Right now, there is a single property 162 * @no-long-family-names available if FreeType is compiled with 163 * PCF_CONFIG_OPTION_LONG_FAMILY_NAMES. 164 * 165 * The PCF driver's module name is 'pcf'. 166 * 167 */ 168 169 170 /************************************************************************** 171 * 172 * @section: 173 * t1_cid_driver 174 * 175 * @title: 176 * The Type 1 and CID drivers 177 * 178 * @abstract: 179 * Controlling the Type~1 and CID driver modules. 180 * 181 * @description: 182 * It is possible to control the behaviour of FreeType's Type~1 and 183 * Type~1 CID drivers with @FT_Property_Set and @FT_Property_Get. 184 * 185 * Behind the scenes, both drivers use the Adobe CFF engine for hinting; 186 * however, the used properties must be specified separately. 187 * 188 * The Type~1 driver's module name is 'type1'; the CID driver's module 189 * name is 't1cid'. 190 * 191 * Available properties are @hinting-engine, @no-stem-darkening, 192 * @darkening-parameters, and @random-seed, as documented in the 193 * @properties section. 194 * 195 * Please see the @cff_driver section for more details on the new hinting 196 * engine. 197 * 198 */ 199 200 201 /************************************************************************** 202 * 203 * @section: 204 * tt_driver 205 * 206 * @title: 207 * The TrueType driver 208 * 209 * @abstract: 210 * Controlling the TrueType driver module. 211 * 212 * @description: 213 * While FreeType's TrueType driver doesn't expose API functions by 214 * itself, it is possible to control its behaviour with @FT_Property_Set 215 * and @FT_Property_Get. The following lists the available properties 216 * together with the necessary macros and structures. 217 * 218 * The TrueType driver's module name is 'truetype'. 219 * 220 * A single property @interpreter-version is available, as documented in 221 * the @properties section. 222 * 223 * We start with a list of definitions, kindly provided by Greg 224 * Hitchcock. 225 * 226 * _Bi-Level Rendering_ 227 * 228 * Monochromatic rendering, exclusively used in the early days of 229 * TrueType by both Apple and Microsoft. Microsoft's GDI interface 230 * supported hinting of the right-side bearing point, such that the 231 * advance width could be non-linear. Most often this was done to 232 * achieve some level of glyph symmetry. To enable reasonable 233 * performance (e.g., not having to run hinting on all glyphs just to get 234 * the widths) there was a bit in the head table indicating if the side 235 * bearing was hinted, and additional tables, 'hdmx' and 'LTSH', to cache 236 * hinting widths across multiple sizes and device aspect ratios. 237 * 238 * _Font Smoothing_ 239 * 240 * Microsoft's GDI implementation of anti-aliasing. Not traditional 241 * anti-aliasing as the outlines were hinted before the sampling. The 242 * widths matched the bi-level rendering. 243 * 244 * _ClearType Rendering_ 245 * 246 * Technique that uses physical subpixels to improve rendering on LCD 247 * (and other) displays. Because of the higher resolution, many methods 248 * of improving symmetry in glyphs through hinting the right-side bearing 249 * were no longer necessary. This lead to what GDI calls 'natural 250 * widths' ClearType, see 251 * http://rastertragedy.com/RTRCh4.htm#Sec21. Since hinting 252 * has extra resolution, most non-linearity went away, but it is still 253 * possible for hints to change the advance widths in this mode. 254 * 255 * _ClearType Compatible Widths_ 256 * 257 * One of the earliest challenges with ClearType was allowing the 258 * implementation in GDI to be selected without requiring all UI and 259 * documents to reflow. To address this, a compatible method of 260 * rendering ClearType was added where the font hints are executed once 261 * to determine the width in bi-level rendering, and then re-run in 262 * ClearType, with the difference in widths being absorbed in the font 263 * hints for ClearType (mostly in the white space of hints); see 264 * http://rastertragedy.com/RTRCh4.htm#Sec20. Somewhat by 265 * definition, compatible width ClearType allows for non-linear widths, 266 * but only when the bi-level version has non-linear widths. 267 * 268 * _ClearType Subpixel Positioning_ 269 * 270 * One of the nice benefits of ClearType is the ability to more crisply 271 * display fractional widths; unfortunately, the GDI model of integer 272 * bitmaps did not support this. However, the WPF and Direct Write 273 * frameworks do support fractional widths. DWrite calls this 'natural 274 * mode', not to be confused with GDI's 'natural widths'. Subpixel 275 * positioning, in the current implementation of Direct Write, 276 * unfortunately does not support hinted advance widths, see 277 * http://rastertragedy.com/RTRCh4.htm#Sec22. Note that the 278 * TrueType interpreter fully allows the advance width to be adjusted in 279 * this mode, just the DWrite client will ignore those changes. 280 * 281 * _ClearType Backward Compatibility_ 282 * 283 * This is a set of exceptions made in the TrueType interpreter to 284 * minimize hinting techniques that were problematic with the extra 285 * resolution of ClearType; see 286 * http://rastertragedy.com/RTRCh4.htm#Sec1 and 287 * https://www.microsoft.com/typography/cleartype/truetypecleartype.aspx. 288 * This technique is not to be confused with ClearType compatible widths. 289 * ClearType backward compatibility has no direct impact on changing 290 * advance widths, but there might be an indirect impact on disabling 291 * some deltas. This could be worked around in backward compatibility 292 * mode. 293 * 294 * _Native ClearType Mode_ 295 * 296 * (Not to be confused with 'natural widths'.) This mode removes all the 297 * exceptions in the TrueType interpreter when running with ClearType. 298 * Any issues on widths would still apply, though. 299 * 300 */ 301 302 303 /************************************************************************** 304 * 305 * @section: 306 * properties 307 * 308 * @title: 309 * Driver properties 310 * 311 * @abstract: 312 * Controlling driver modules. 313 * 314 * @description: 315 * Driver modules can be controlled by setting and unsetting properties, 316 * using the functions @FT_Property_Set and @FT_Property_Get. This 317 * section documents the available properties, together with auxiliary 318 * macros and structures. 319 * 320 */ 321 322 323 /************************************************************************** 324 * 325 * @enum: 326 * FT_HINTING_XXX 327 * 328 * @description: 329 * A list of constants used for the @hinting-engine property to select 330 * the hinting engine for CFF, Type~1, and CID fonts. 331 * 332 * @values: 333 * FT_HINTING_FREETYPE :: 334 * Use the old FreeType hinting engine. 335 * 336 * FT_HINTING_ADOBE :: 337 * Use the hinting engine contributed by Adobe. 338 * 339 * @since: 340 * 2.9 341 * 342 */ 343 #define FT_HINTING_FREETYPE 0 344 #define FT_HINTING_ADOBE 1 345 346 /* these constants (introduced in 2.4.12) are deprecated */ 347 #define FT_CFF_HINTING_FREETYPE FT_HINTING_FREETYPE 348 #define FT_CFF_HINTING_ADOBE FT_HINTING_ADOBE 349 350 351 /************************************************************************** 352 * 353 * @property: 354 * hinting-engine 355 * 356 * @description: 357 * Thanks to Adobe, which contributed a new hinting (and parsing) engine, 358 * an application can select between 'freetype' and 'adobe' if compiled 359 * with `CFF_CONFIG_OPTION_OLD_ENGINE`. If this configuration macro 360 * isn't defined, 'hinting-engine' does nothing. 361 * 362 * The same holds for the Type~1 and CID modules if compiled with 363 * `T1_CONFIG_OPTION_OLD_ENGINE`. 364 * 365 * For the 'cff' module, the default engine is 'adobe'. For both the 366 * 'type1' and 't1cid' modules, the default engine is 'adobe', too. 367 * 368 * @note: 369 * This property can be used with @FT_Property_Get also. 370 * 371 * This property can be set via the `FREETYPE_PROPERTIES` environment 372 * variable (using values 'adobe' or 'freetype'). 373 * 374 * @example: 375 * The following example code demonstrates how to select Adobe's hinting 376 * engine for the 'cff' module (omitting the error handling). 377 * 378 * ``` 379 * FT_Library library; 380 * FT_UInt hinting_engine = FT_HINTING_ADOBE; 381 * 382 * 383 * FT_Init_FreeType( &library ); 384 * 385 * FT_Property_Set( library, "cff", 386 * "hinting-engine", &hinting_engine ); 387 * ``` 388 * 389 * @since: 390 * 2.4.12 (for 'cff' module) 391 * 392 * 2.9 (for 'type1' and 't1cid' modules) 393 * 394 */ 395 396 397 /************************************************************************** 398 * 399 * @property: 400 * no-stem-darkening 401 * 402 * @description: 403 * All glyphs that pass through the auto-hinter will be emboldened unless 404 * this property is set to TRUE. The same is true for the CFF, Type~1, 405 * and CID font modules if the 'Adobe' engine is selected (which is the 406 * default). 407 * 408 * Stem darkening emboldens glyphs at smaller sizes to make them more 409 * readable on common low-DPI screens when using linear alpha blending 410 * and gamma correction, see @FT_Render_Glyph. When not using linear 411 * alpha blending and gamma correction, glyphs will appear heavy and 412 * fuzzy! 413 * 414 * Gamma correction essentially lightens fonts since shades of grey are 415 * shifted to higher pixel values (=~higher brightness) to match the 416 * original intention to the reality of our screens. The side-effect is 417 * that glyphs 'thin out'. Mac OS~X and Adobe's proprietary font 418 * rendering library implement a counter-measure: stem darkening at 419 * smaller sizes where shades of gray dominate. By emboldening a glyph 420 * slightly in relation to its pixel size, individual pixels get higher 421 * coverage of filled-in outlines and are therefore 'blacker'. This 422 * counteracts the 'thinning out' of glyphs, making text remain readable 423 * at smaller sizes. 424 * 425 * For the auto-hinter, stem-darkening is experimental currently and thus 426 * switched off by default (this is, `no-stem-darkening` is set to TRUE 427 * by default). Total consistency with the CFF driver is not achieved 428 * right now because the emboldening method differs and glyphs must be 429 * scaled down on the Y-axis to keep outline points inside their 430 * precomputed blue zones. The smaller the size (especially 9ppem and 431 * down), the higher the loss of emboldening versus the CFF driver. 432 * 433 * Note that stem darkening is never applied if @FT_LOAD_NO_SCALE is set. 434 * 435 * @note: 436 * This property can be used with @FT_Property_Get also. 437 * 438 * This property can be set via the `FREETYPE_PROPERTIES` environment 439 * variable (using values 1 and 0 for 'on' and 'off', respectively). It 440 * can also be set per face using @FT_Face_Properties with 441 * @FT_PARAM_TAG_STEM_DARKENING. 442 * 443 * @example: 444 * ``` 445 * FT_Library library; 446 * FT_Bool no_stem_darkening = TRUE; 447 * 448 * 449 * FT_Init_FreeType( &library ); 450 * 451 * FT_Property_Set( library, "cff", 452 * "no-stem-darkening", &no_stem_darkening ); 453 * ``` 454 * 455 * @since: 456 * 2.4.12 (for 'cff' module) 457 * 458 * 2.6.2 (for 'autofitter' module) 459 * 460 * 2.9 (for 'type1' and 't1cid' modules) 461 * 462 */ 463 464 465 /************************************************************************** 466 * 467 * @property: 468 * darkening-parameters 469 * 470 * @description: 471 * By default, the Adobe hinting engine, as used by the CFF, Type~1, and 472 * CID font drivers, darkens stems as follows (if the `no-stem-darkening` 473 * property isn't set): 474 * 475 * ``` 476 * stem width <= 0.5px: darkening amount = 0.4px 477 * stem width = 1px: darkening amount = 0.275px 478 * stem width = 1.667px: darkening amount = 0.275px 479 * stem width >= 2.333px: darkening amount = 0px 480 * ``` 481 * 482 * and piecewise linear in-between. At configuration time, these four 483 * control points can be set with the macro 484 * `CFF_CONFIG_OPTION_DARKENING_PARAMETERS`; the CFF, Type~1, and CID 485 * drivers share these values. At runtime, the control points can be 486 * changed using the `darkening-parameters` property (see the example 487 * below that demonstrates this for the Type~1 driver). 488 * 489 * The x~values give the stem width, and the y~values the darkening 490 * amount. The unit is 1000th of pixels. All coordinate values must be 491 * positive; the x~values must be monotonically increasing; the y~values 492 * must be monotonically decreasing and smaller than or equal to 500 493 * (corresponding to half a pixel); the slope of each linear piece must 494 * be shallower than -1 (e.g., -.4). 495 * 496 * The auto-hinter provides this property, too, as an experimental 497 * feature. See @no-stem-darkening for more. 498 * 499 * @note: 500 * This property can be used with @FT_Property_Get also. 501 * 502 * This property can be set via the `FREETYPE_PROPERTIES` environment 503 * variable, using eight comma-separated integers without spaces. Here 504 * the above example, using `\` to break the line for readability. 505 * 506 * ``` 507 * FREETYPE_PROPERTIES=\ 508 * type1:darkening-parameters=500,300,1000,200,1500,100,2000,0 509 * ``` 510 * 511 * @example: 512 * ``` 513 * FT_Library library; 514 * FT_Int darken_params[8] = { 500, 300, // x1, y1 515 * 1000, 200, // x2, y2 516 * 1500, 100, // x3, y3 517 * 2000, 0 }; // x4, y4 518 * 519 * 520 * FT_Init_FreeType( &library ); 521 * 522 * FT_Property_Set( library, "type1", 523 * "darkening-parameters", darken_params ); 524 * ``` 525 * 526 * @since: 527 * 2.5.1 (for 'cff' module) 528 * 529 * 2.6.2 (for 'autofitter' module) 530 * 531 * 2.9 (for 'type1' and 't1cid' modules) 532 * 533 */ 534 535 536 /************************************************************************** 537 * 538 * @property: 539 * random-seed 540 * 541 * @description: 542 * By default, the seed value for the CFF 'random' operator and the 543 * similar '0 28 callothersubr pop' command for the Type~1 and CID 544 * drivers is set to a random value. However, mainly for debugging 545 * purposes, it is often necessary to use a known value as a seed so that 546 * the pseudo-random number sequences generated by 'random' are 547 * repeatable. 548 * 549 * The `random-seed` property does that. Its argument is a signed 32bit 550 * integer; if the value is zero or negative, the seed given by the 551 * `intitialRandomSeed` private DICT operator in a CFF file gets used (or 552 * a default value if there is no such operator). If the value is 553 * positive, use it instead of `initialRandomSeed`, which is consequently 554 * ignored. 555 * 556 * @note: 557 * This property can be set via the `FREETYPE_PROPERTIES` environment 558 * variable. It can also be set per face using @FT_Face_Properties with 559 * @FT_PARAM_TAG_RANDOM_SEED. 560 * 561 * @since: 562 * 2.8 (for 'cff' module) 563 * 564 * 2.9 (for 'type1' and 't1cid' modules) 565 * 566 */ 567 568 569 /************************************************************************** 570 * 571 * @property: 572 * no-long-family-names 573 * 574 * @description: 575 * If `PCF_CONFIG_OPTION_LONG_FAMILY_NAMES` is active while compiling 576 * FreeType, the PCF driver constructs long family names. 577 * 578 * There are many PCF fonts just called 'Fixed' which look completely 579 * different, and which have nothing to do with each other. When 580 * selecting 'Fixed' in KDE or Gnome one gets results that appear rather 581 * random, the style changes often if one changes the size and one cannot 582 * select some fonts at all. The improve this situation, the PCF module 583 * prepends the foundry name (plus a space) to the family name. It also 584 * checks whether there are 'wide' characters; all put together, family 585 * names like 'Sony Fixed' or 'Misc Fixed Wide' are constructed. 586 * 587 * If `no-long-family-names` is set, this feature gets switched off. 588 * 589 * @note: 590 * This property can be used with @FT_Property_Get also. 591 * 592 * This property can be set via the `FREETYPE_PROPERTIES` environment 593 * variable (using values 1 and 0 for 'on' and 'off', respectively). 594 * 595 * @example: 596 * ``` 597 * FT_Library library; 598 * FT_Bool no_long_family_names = TRUE; 599 * 600 * 601 * FT_Init_FreeType( &library ); 602 * 603 * FT_Property_Set( library, "pcf", 604 * "no-long-family-names", 605 * &no_long_family_names ); 606 * ``` 607 * 608 * @since: 609 * 2.8 610 */ 611 612 613 /************************************************************************** 614 * 615 * @enum: 616 * TT_INTERPRETER_VERSION_XXX 617 * 618 * @description: 619 * A list of constants used for the @interpreter-version property to 620 * select the hinting engine for Truetype fonts. 621 * 622 * The numeric value in the constant names represents the version number 623 * as returned by the 'GETINFO' bytecode instruction. 624 * 625 * @values: 626 * TT_INTERPRETER_VERSION_35 :: 627 * Version~35 corresponds to MS rasterizer v.1.7 as used e.g. in 628 * Windows~98; only grayscale and B/W rasterizing is supported. 629 * 630 * TT_INTERPRETER_VERSION_38 :: 631 * Version~38 corresponds to MS rasterizer v.1.9; it is roughly 632 * equivalent to the hinting provided by DirectWrite ClearType (as can 633 * be found, for example, in the Internet Explorer~9 running on 634 * Windows~7). It is used in FreeType to select the 'Infinality' 635 * subpixel hinting code. The code may be removed in a future version. 636 * 637 * TT_INTERPRETER_VERSION_40 :: 638 * Version~40 corresponds to MS rasterizer v.2.1; it is roughly 639 * equivalent to the hinting provided by DirectWrite ClearType (as can 640 * be found, for example, in Microsoft's Edge Browser on Windows~10). 641 * It is used in FreeType to select the 'minimal' subpixel hinting 642 * code, a stripped-down and higher performance version of the 643 * 'Infinality' code. 644 * 645 * @note: 646 * This property controls the behaviour of the bytecode interpreter and 647 * thus how outlines get hinted. It does **not** control how glyph get 648 * rasterized! In particular, it does not control subpixel color 649 * filtering. 650 * 651 * If FreeType has not been compiled with the configuration option 652 * `TT_CONFIG_OPTION_SUBPIXEL_HINTING`, selecting version~38 or~40 causes 653 * an `FT_Err_Unimplemented_Feature` error. 654 * 655 * Depending on the graphics framework, Microsoft uses different bytecode 656 * and rendering engines. As a consequence, the version numbers returned 657 * by a call to the 'GETINFO' bytecode instruction are more convoluted 658 * than desired. 659 * 660 * Here are two tables that try to shed some light on the possible values 661 * for the MS rasterizer engine, together with the additional features 662 * introduced by it. 663 * 664 * ``` 665 * GETINFO framework version feature 666 * ------------------------------------------------------------------- 667 * 3 GDI (Win 3.1), v1.0 16-bit, first version 668 * TrueImage 669 * 33 GDI (Win NT 3.1), v1.5 32-bit 670 * HP Laserjet 671 * 34 GDI (Win 95) v1.6 font smoothing, 672 * new SCANTYPE opcode 673 * 35 GDI (Win 98/2000) v1.7 (UN)SCALED_COMPONENT_OFFSET 674 * bits in composite glyphs 675 * 36 MGDI (Win CE 2) v1.6+ classic ClearType 676 * 37 GDI (XP and later), v1.8 ClearType 677 * GDI+ old (before Vista) 678 * 38 GDI+ old (Vista, Win 7), v1.9 subpixel ClearType, 679 * WPF Y-direction ClearType, 680 * additional error checking 681 * 39 DWrite (before Win 8) v2.0 subpixel ClearType flags 682 * in GETINFO opcode, 683 * bug fixes 684 * 40 GDI+ (after Win 7), v2.1 Y-direction ClearType flag 685 * DWrite (Win 8) in GETINFO opcode, 686 * Gray ClearType 687 * ``` 688 * 689 * The 'version' field gives a rough orientation only, since some 690 * applications provided certain features much earlier (as an example, 691 * Microsoft Reader used subpixel and Y-direction ClearType already in 692 * Windows 2000). Similarly, updates to a given framework might include 693 * improved hinting support. 694 * 695 * ``` 696 * version sampling rendering comment 697 * x y x y 698 * -------------------------------------------------------------- 699 * v1.0 normal normal B/W B/W bi-level 700 * v1.6 high high gray gray grayscale 701 * v1.8 high normal color-filter B/W (GDI) ClearType 702 * v1.9 high high color-filter gray Color ClearType 703 * v2.1 high normal gray B/W Gray ClearType 704 * v2.1 high high gray gray Gray ClearType 705 * ``` 706 * 707 * Color and Gray ClearType are the two available variants of 708 * 'Y-direction ClearType', meaning grayscale rasterization along the 709 * Y-direction; the name used in the TrueType specification for this 710 * feature is 'symmetric smoothing'. 'Classic ClearType' is the original 711 * algorithm used before introducing a modified version in Win~XP. 712 * Another name for v1.6's grayscale rendering is 'font smoothing', and 713 * 'Color ClearType' is sometimes also called 'DWrite ClearType'. To 714 * differentiate between today's Color ClearType and the earlier 715 * ClearType variant with B/W rendering along the vertical axis, the 716 * latter is sometimes called 'GDI ClearType'. 717 * 718 * 'Normal' and 'high' sampling describe the (virtual) resolution to 719 * access the rasterized outline after the hinting process. 'Normal' 720 * means 1 sample per grid line (i.e., B/W). In the current Microsoft 721 * implementation, 'high' means an extra virtual resolution of 16x16 (or 722 * 16x1) grid lines per pixel for bytecode instructions like 'MIRP'. 723 * After hinting, these 16 grid lines are mapped to 6x5 (or 6x1) grid 724 * lines for color filtering if Color ClearType is activated. 725 * 726 * Note that 'Gray ClearType' is essentially the same as v1.6's grayscale 727 * rendering. However, the GETINFO instruction handles it differently: 728 * v1.6 returns bit~12 (hinting for grayscale), while v2.1 returns 729 * bits~13 (hinting for ClearType), 18 (symmetrical smoothing), and~19 730 * (Gray ClearType). Also, this mode respects bits 2 and~3 for the 731 * version~1 gasp table exclusively (like Color ClearType), while v1.6 732 * only respects the values of version~0 (bits 0 and~1). 733 * 734 * Keep in mind that the features of the above interpreter versions might 735 * not map exactly to FreeType features or behavior because it is a 736 * fundamentally different library with different internals. 737 * 738 */ 739 #define TT_INTERPRETER_VERSION_35 35 740 #define TT_INTERPRETER_VERSION_38 38 741 #define TT_INTERPRETER_VERSION_40 40 742 743 744 /************************************************************************** 745 * 746 * @property: 747 * interpreter-version 748 * 749 * @description: 750 * Currently, three versions are available, two representing the bytecode 751 * interpreter with subpixel hinting support (old 'Infinality' code and 752 * new stripped-down and higher performance 'minimal' code) and one 753 * without, respectively. The default is subpixel support if 754 * `TT_CONFIG_OPTION_SUBPIXEL_HINTING` is defined, and no subpixel 755 * support otherwise (since it isn't available then). 756 * 757 * If subpixel hinting is on, many TrueType bytecode instructions behave 758 * differently compared to B/W or grayscale rendering (except if 'native 759 * ClearType' is selected by the font). Microsoft's main idea is to 760 * render at a much increased horizontal resolution, then sampling down 761 * the created output to subpixel precision. However, many older fonts 762 * are not suited to this and must be specially taken care of by applying 763 * (hardcoded) tweaks in Microsoft's interpreter. 764 * 765 * Details on subpixel hinting and some of the necessary tweaks can be 766 * found in Greg Hitchcock's whitepaper at 767 * 'https://www.microsoft.com/typography/cleartype/truetypecleartype.aspx'. 768 * Note that FreeType currently doesn't really 'subpixel hint' (6x1, 6x2, 769 * or 6x5 supersampling) like discussed in the paper. Depending on the 770 * chosen interpreter, it simply ignores instructions on vertical stems 771 * to arrive at very similar results. 772 * 773 * @note: 774 * This property can be used with @FT_Property_Get also. 775 * 776 * This property can be set via the `FREETYPE_PROPERTIES` environment 777 * variable (using values '35', '38', or '40'). 778 * 779 * @example: 780 * The following example code demonstrates how to deactivate subpixel 781 * hinting (omitting the error handling). 782 * 783 * ``` 784 * FT_Library library; 785 * FT_Face face; 786 * FT_UInt interpreter_version = TT_INTERPRETER_VERSION_35; 787 * 788 * 789 * FT_Init_FreeType( &library ); 790 * 791 * FT_Property_Set( library, "truetype", 792 * "interpreter-version", 793 * &interpreter_version ); 794 * ``` 795 * 796 * @since: 797 * 2.5 798 */ 799 800 801 /************************************************************************** 802 * 803 * @property: 804 * glyph-to-script-map 805 * 806 * @description: 807 * **Experimental only** 808 * 809 * The auto-hinter provides various script modules to hint glyphs. 810 * Examples of supported scripts are Latin or CJK. Before a glyph is 811 * auto-hinted, the Unicode character map of the font gets examined, and 812 * the script is then determined based on Unicode character ranges, see 813 * below. 814 * 815 * OpenType fonts, however, often provide much more glyphs than character 816 * codes (small caps, superscripts, ligatures, swashes, etc.), to be 817 * controlled by so-called 'features'. Handling OpenType features can be 818 * quite complicated and thus needs a separate library on top of 819 * FreeType. 820 * 821 * The mapping between glyph indices and scripts (in the auto-hinter 822 * sense, see the @FT_AUTOHINTER_SCRIPT_XXX values) is stored as an array 823 * with `num_glyphs` elements, as found in the font's @FT_Face structure. 824 * The `glyph-to-script-map` property returns a pointer to this array, 825 * which can be modified as needed. Note that the modification should 826 * happen before the first glyph gets processed by the auto-hinter so 827 * that the global analysis of the font shapes actually uses the modified 828 * mapping. 829 * 830 * @example: 831 * The following example code demonstrates how to access it (omitting the 832 * error handling). 833 * 834 * ``` 835 * FT_Library library; 836 * FT_Face face; 837 * FT_Prop_GlyphToScriptMap prop; 838 * 839 * 840 * FT_Init_FreeType( &library ); 841 * FT_New_Face( library, "foo.ttf", 0, &face ); 842 * 843 * prop.face = face; 844 * 845 * FT_Property_Get( library, "autofitter", 846 * "glyph-to-script-map", &prop ); 847 * 848 * // adjust `prop.map' as needed right here 849 * 850 * FT_Load_Glyph( face, ..., FT_LOAD_FORCE_AUTOHINT ); 851 * ``` 852 * 853 * @since: 854 * 2.4.11 855 * 856 */ 857 858 859 /************************************************************************** 860 * 861 * @enum: 862 * FT_AUTOHINTER_SCRIPT_XXX 863 * 864 * @description: 865 * **Experimental only** 866 * 867 * A list of constants used for the @glyph-to-script-map property to 868 * specify the script submodule the auto-hinter should use for hinting a 869 * particular glyph. 870 * 871 * @values: 872 * FT_AUTOHINTER_SCRIPT_NONE :: 873 * Don't auto-hint this glyph. 874 * 875 * FT_AUTOHINTER_SCRIPT_LATIN :: 876 * Apply the latin auto-hinter. For the auto-hinter, 'latin' is a very 877 * broad term, including Cyrillic and Greek also since characters from 878 * those scripts share the same design constraints. 879 * 880 * By default, characters from the following Unicode ranges are 881 * assigned to this submodule. 882 * 883 * ``` 884 * U+0020 - U+007F // Basic Latin (no control characters) 885 * U+00A0 - U+00FF // Latin-1 Supplement (no control characters) 886 * U+0100 - U+017F // Latin Extended-A 887 * U+0180 - U+024F // Latin Extended-B 888 * U+0250 - U+02AF // IPA Extensions 889 * U+02B0 - U+02FF // Spacing Modifier Letters 890 * U+0300 - U+036F // Combining Diacritical Marks 891 * U+0370 - U+03FF // Greek and Coptic 892 * U+0400 - U+04FF // Cyrillic 893 * U+0500 - U+052F // Cyrillic Supplement 894 * U+1D00 - U+1D7F // Phonetic Extensions 895 * U+1D80 - U+1DBF // Phonetic Extensions Supplement 896 * U+1DC0 - U+1DFF // Combining Diacritical Marks Supplement 897 * U+1E00 - U+1EFF // Latin Extended Additional 898 * U+1F00 - U+1FFF // Greek Extended 899 * U+2000 - U+206F // General Punctuation 900 * U+2070 - U+209F // Superscripts and Subscripts 901 * U+20A0 - U+20CF // Currency Symbols 902 * U+2150 - U+218F // Number Forms 903 * U+2460 - U+24FF // Enclosed Alphanumerics 904 * U+2C60 - U+2C7F // Latin Extended-C 905 * U+2DE0 - U+2DFF // Cyrillic Extended-A 906 * U+2E00 - U+2E7F // Supplemental Punctuation 907 * U+A640 - U+A69F // Cyrillic Extended-B 908 * U+A720 - U+A7FF // Latin Extended-D 909 * U+FB00 - U+FB06 // Alphab. Present. Forms (Latin Ligatures) 910 * U+1D400 - U+1D7FF // Mathematical Alphanumeric Symbols 911 * U+1F100 - U+1F1FF // Enclosed Alphanumeric Supplement 912 * ``` 913 * 914 * FT_AUTOHINTER_SCRIPT_CJK :: 915 * Apply the CJK auto-hinter, covering Chinese, Japanese, Korean, old 916 * Vietnamese, and some other scripts. 917 * 918 * By default, characters from the following Unicode ranges are 919 * assigned to this submodule. 920 * 921 * ``` 922 * U+1100 - U+11FF // Hangul Jamo 923 * U+2E80 - U+2EFF // CJK Radicals Supplement 924 * U+2F00 - U+2FDF // Kangxi Radicals 925 * U+2FF0 - U+2FFF // Ideographic Description Characters 926 * U+3000 - U+303F // CJK Symbols and Punctuation 927 * U+3040 - U+309F // Hiragana 928 * U+30A0 - U+30FF // Katakana 929 * U+3100 - U+312F // Bopomofo 930 * U+3130 - U+318F // Hangul Compatibility Jamo 931 * U+3190 - U+319F // Kanbun 932 * U+31A0 - U+31BF // Bopomofo Extended 933 * U+31C0 - U+31EF // CJK Strokes 934 * U+31F0 - U+31FF // Katakana Phonetic Extensions 935 * U+3200 - U+32FF // Enclosed CJK Letters and Months 936 * U+3300 - U+33FF // CJK Compatibility 937 * U+3400 - U+4DBF // CJK Unified Ideographs Extension A 938 * U+4DC0 - U+4DFF // Yijing Hexagram Symbols 939 * U+4E00 - U+9FFF // CJK Unified Ideographs 940 * U+A960 - U+A97F // Hangul Jamo Extended-A 941 * U+AC00 - U+D7AF // Hangul Syllables 942 * U+D7B0 - U+D7FF // Hangul Jamo Extended-B 943 * U+F900 - U+FAFF // CJK Compatibility Ideographs 944 * U+FE10 - U+FE1F // Vertical forms 945 * U+FE30 - U+FE4F // CJK Compatibility Forms 946 * U+FF00 - U+FFEF // Halfwidth and Fullwidth Forms 947 * U+1B000 - U+1B0FF // Kana Supplement 948 * U+1D300 - U+1D35F // Tai Xuan Hing Symbols 949 * U+1F200 - U+1F2FF // Enclosed Ideographic Supplement 950 * U+20000 - U+2A6DF // CJK Unified Ideographs Extension B 951 * U+2A700 - U+2B73F // CJK Unified Ideographs Extension C 952 * U+2B740 - U+2B81F // CJK Unified Ideographs Extension D 953 * U+2F800 - U+2FA1F // CJK Compatibility Ideographs Supplement 954 * ``` 955 * 956 * FT_AUTOHINTER_SCRIPT_INDIC :: 957 * Apply the indic auto-hinter, covering all major scripts from the 958 * Indian sub-continent and some other related scripts like Thai, Lao, 959 * or Tibetan. 960 * 961 * By default, characters from the following Unicode ranges are 962 * assigned to this submodule. 963 * 964 * ``` 965 * U+0900 - U+0DFF // Indic Range 966 * U+0F00 - U+0FFF // Tibetan 967 * U+1900 - U+194F // Limbu 968 * U+1B80 - U+1BBF // Sundanese 969 * U+A800 - U+A82F // Syloti Nagri 970 * U+ABC0 - U+ABFF // Meetei Mayek 971 * U+11800 - U+118DF // Sharada 972 * ``` 973 * 974 * Note that currently Indic support is rudimentary only, missing blue 975 * zone support. 976 * 977 * @since: 978 * 2.4.11 979 * 980 */ 981 #define FT_AUTOHINTER_SCRIPT_NONE 0 982 #define FT_AUTOHINTER_SCRIPT_LATIN 1 983 #define FT_AUTOHINTER_SCRIPT_CJK 2 984 #define FT_AUTOHINTER_SCRIPT_INDIC 3 985 986 987 /************************************************************************** 988 * 989 * @struct: 990 * FT_Prop_GlyphToScriptMap 991 * 992 * @description: 993 * **Experimental only** 994 * 995 * The data exchange structure for the @glyph-to-script-map property. 996 * 997 * @since: 998 * 2.4.11 999 * 1000 */ 1001 typedef struct FT_Prop_GlyphToScriptMap_ 1002 { 1003 FT_Face face; 1004 FT_UShort* map; 1005 1006 } FT_Prop_GlyphToScriptMap; 1007 1008 1009 /************************************************************************** 1010 * 1011 * @property: 1012 * fallback-script 1013 * 1014 * @description: 1015 * **Experimental only** 1016 * 1017 * If no auto-hinter script module can be assigned to a glyph, a fallback 1018 * script gets assigned to it (see also the @glyph-to-script-map 1019 * property). By default, this is @FT_AUTOHINTER_SCRIPT_CJK. Using the 1020 * `fallback-script` property, this fallback value can be changed. 1021 * 1022 * @note: 1023 * This property can be used with @FT_Property_Get also. 1024 * 1025 * It's important to use the right timing for changing this value: The 1026 * creation of the glyph-to-script map that eventually uses the fallback 1027 * script value gets triggered either by setting or reading a 1028 * face-specific property like @glyph-to-script-map, or by auto-hinting 1029 * any glyph from that face. In particular, if you have already created 1030 * an @FT_Face structure but not loaded any glyph (using the 1031 * auto-hinter), a change of the fallback script will affect this face. 1032 * 1033 * @example: 1034 * ``` 1035 * FT_Library library; 1036 * FT_UInt fallback_script = FT_AUTOHINTER_SCRIPT_NONE; 1037 * 1038 * 1039 * FT_Init_FreeType( &library ); 1040 * 1041 * FT_Property_Set( library, "autofitter", 1042 * "fallback-script", &fallback_script ); 1043 * ``` 1044 * 1045 * @since: 1046 * 2.4.11 1047 * 1048 */ 1049 1050 1051 /************************************************************************** 1052 * 1053 * @property: 1054 * default-script 1055 * 1056 * @description: 1057 * **Experimental only** 1058 * 1059 * If FreeType gets compiled with `FT_CONFIG_OPTION_USE_HARFBUZZ` to make 1060 * the HarfBuzz library access OpenType features for getting better glyph 1061 * coverages, this property sets the (auto-fitter) script to be used for 1062 * the default (OpenType) script data of a font's GSUB table. Features 1063 * for the default script are intended for all scripts not explicitly 1064 * handled in GSUB; an example is a 'dlig' feature, containing the 1065 * combination of the characters 'T', 'E', and 'L' to form a 'TEL' 1066 * ligature. 1067 * 1068 * By default, this is @FT_AUTOHINTER_SCRIPT_LATIN. Using the 1069 * `default-script` property, this default value can be changed. 1070 * 1071 * @note: 1072 * This property can be used with @FT_Property_Get also. 1073 * 1074 * It's important to use the right timing for changing this value: The 1075 * creation of the glyph-to-script map that eventually uses the default 1076 * script value gets triggered either by setting or reading a 1077 * face-specific property like @glyph-to-script-map, or by auto-hinting 1078 * any glyph from that face. In particular, if you have already created 1079 * an @FT_Face structure but not loaded any glyph (using the 1080 * auto-hinter), a change of the default script will affect this face. 1081 * 1082 * @example: 1083 * ``` 1084 * FT_Library library; 1085 * FT_UInt default_script = FT_AUTOHINTER_SCRIPT_NONE; 1086 * 1087 * 1088 * FT_Init_FreeType( &library ); 1089 * 1090 * FT_Property_Set( library, "autofitter", 1091 * "default-script", &default_script ); 1092 * ``` 1093 * 1094 * @since: 1095 * 2.5.3 1096 * 1097 */ 1098 1099 1100 /************************************************************************** 1101 * 1102 * @property: 1103 * increase-x-height 1104 * 1105 * @description: 1106 * For ppem values in the range 6~<= ppem <= `increase-x-height`, round 1107 * up the font's x~height much more often than normally. If the value is 1108 * set to~0, which is the default, this feature is switched off. Use 1109 * this property to improve the legibility of small font sizes if 1110 * necessary. 1111 * 1112 * @note: 1113 * This property can be used with @FT_Property_Get also. 1114 * 1115 * Set this value right after calling @FT_Set_Char_Size, but before 1116 * loading any glyph (using the auto-hinter). 1117 * 1118 * @example: 1119 * ``` 1120 * FT_Library library; 1121 * FT_Face face; 1122 * FT_Prop_IncreaseXHeight prop; 1123 * 1124 * 1125 * FT_Init_FreeType( &library ); 1126 * FT_New_Face( library, "foo.ttf", 0, &face ); 1127 * FT_Set_Char_Size( face, 10 * 64, 0, 72, 0 ); 1128 * 1129 * prop.face = face; 1130 * prop.limit = 14; 1131 * 1132 * FT_Property_Set( library, "autofitter", 1133 * "increase-x-height", &prop ); 1134 * ``` 1135 * 1136 * @since: 1137 * 2.4.11 1138 * 1139 */ 1140 1141 1142 /************************************************************************** 1143 * 1144 * @struct: 1145 * FT_Prop_IncreaseXHeight 1146 * 1147 * @description: 1148 * The data exchange structure for the @increase-x-height property. 1149 * 1150 */ 1151 typedef struct FT_Prop_IncreaseXHeight_ 1152 { 1153 FT_Face face; 1154 FT_UInt limit; 1155 1156 } FT_Prop_IncreaseXHeight; 1157 1158 1159 /************************************************************************** 1160 * 1161 * @property: 1162 * warping 1163 * 1164 * @description: 1165 * **Obsolete** 1166 * 1167 * This property was always experimental and probably never worked 1168 * correctly. It was entirely removed from the FreeType~2 sources. This 1169 * entry is only here for historical reference. 1170 * 1171 * Warping only worked in 'normal' auto-hinting mode replacing it. The 1172 * idea of the code was to slightly scale and shift a glyph along the 1173 * non-hinted dimension (which is usually the horizontal axis) so that as 1174 * much of its segments were aligned (more or less) to the grid. To find 1175 * out a glyph's optimal scaling and shifting value, various parameter 1176 * combinations were tried and scored. 1177 * 1178 * @since: 1179 * 2.6 1180 * 1181 */ 1182 1183 1184 /* */ 1185 1186 1187 FT_END_HEADER 1188 1189 1190 #endif /* FTDRIVER_H_ */ 1191 1192 1193 /* END */ 1194