1 /**************************************************************************** 2 * 3 * ftdriver.h 4 * 5 * FreeType API for controlling driver modules (specification only). 6 * 7 * Copyright (C) 2017-2023 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. 216 * 217 * The TrueType driver's module name is 'truetype'; a single property 218 * @interpreter-version is available, as documented in the @properties 219 * section. 220 * 221 * To help understand the differences between interpreter versions, we 222 * introduce a list of definitions, kindly provided by Greg Hitchcock. 223 * 224 * _Bi-Level Rendering_ 225 * 226 * Monochromatic rendering, exclusively used in the early days of 227 * TrueType by both Apple and Microsoft. Microsoft's GDI interface 228 * supported hinting of the right-side bearing point, such that the 229 * advance width could be non-linear. Most often this was done to 230 * achieve some level of glyph symmetry. To enable reasonable 231 * performance (e.g., not having to run hinting on all glyphs just to get 232 * the widths) there was a bit in the head table indicating if the side 233 * bearing was hinted, and additional tables, 'hdmx' and 'LTSH', to cache 234 * hinting widths across multiple sizes and device aspect ratios. 235 * 236 * _Font Smoothing_ 237 * 238 * Microsoft's GDI implementation of anti-aliasing. Not traditional 239 * anti-aliasing as the outlines were hinted before the sampling. The 240 * widths matched the bi-level rendering. 241 * 242 * _ClearType Rendering_ 243 * 244 * Technique that uses physical subpixels to improve rendering on LCD 245 * (and other) displays. Because of the higher resolution, many methods 246 * of improving symmetry in glyphs through hinting the right-side bearing 247 * were no longer necessary. This lead to what GDI calls 'natural 248 * widths' ClearType, see 249 * http://rastertragedy.com/RTRCh4.htm#Sec21. Since hinting 250 * has extra resolution, most non-linearity went away, but it is still 251 * possible for hints to change the advance widths in this mode. 252 * 253 * _ClearType Compatible Widths_ 254 * 255 * One of the earliest challenges with ClearType was allowing the 256 * implementation in GDI to be selected without requiring all UI and 257 * documents to reflow. To address this, a compatible method of 258 * rendering ClearType was added where the font hints are executed once 259 * to determine the width in bi-level rendering, and then re-run in 260 * ClearType, with the difference in widths being absorbed in the font 261 * hints for ClearType (mostly in the white space of hints); see 262 * http://rastertragedy.com/RTRCh4.htm#Sec20. Somewhat by 263 * definition, compatible width ClearType allows for non-linear widths, 264 * but only when the bi-level version has non-linear widths. 265 * 266 * _ClearType Subpixel Positioning_ 267 * 268 * One of the nice benefits of ClearType is the ability to more crisply 269 * display fractional widths; unfortunately, the GDI model of integer 270 * bitmaps did not support this. However, the WPF and Direct Write 271 * frameworks do support fractional widths. DWrite calls this 'natural 272 * mode', not to be confused with GDI's 'natural widths'. Subpixel 273 * positioning, in the current implementation of Direct Write, 274 * unfortunately does not support hinted advance widths, see 275 * http://rastertragedy.com/RTRCh4.htm#Sec22. Note that the 276 * TrueType interpreter fully allows the advance width to be adjusted in 277 * this mode, just the DWrite client will ignore those changes. 278 * 279 * _ClearType Backward Compatibility_ 280 * 281 * This is a set of exceptions made in the TrueType interpreter to 282 * minimize hinting techniques that were problematic with the extra 283 * resolution of ClearType; see 284 * http://rastertragedy.com/RTRCh4.htm#Sec1 and 285 * https://www.microsoft.com/typography/cleartype/truetypecleartype.aspx. 286 * This technique is not to be confused with ClearType compatible widths. 287 * ClearType backward compatibility has no direct impact on changing 288 * advance widths, but there might be an indirect impact on disabling 289 * some deltas. This could be worked around in backward compatibility 290 * mode. 291 * 292 * _Native ClearType Mode_ 293 * 294 * (Not to be confused with 'natural widths'.) This mode removes all the 295 * exceptions in the TrueType interpreter when running with ClearType. 296 * Any issues on widths would still apply, though. 297 * 298 */ 299 300 301 /************************************************************************** 302 * 303 * @section: 304 * ot_svg_driver 305 * 306 * @title: 307 * The SVG driver 308 * 309 * @abstract: 310 * Controlling the external rendering of OT-SVG glyphs. 311 * 312 * @description: 313 * By default, FreeType can only load the 'SVG~' table of OpenType fonts 314 * if configuration macro `FT_CONFIG_OPTION_SVG` is defined. To make it 315 * render SVG glyphs, an external SVG rendering library is needed. All 316 * details on the interface between FreeType and the external library 317 * via function hooks can be found in section @svg_fonts. 318 * 319 * The OT-SVG driver's module name is 'ot-svg'; it supports a single 320 * property called @svg-hooks, documented below in the @properties 321 * section. 322 * 323 */ 324 325 326 /************************************************************************** 327 * 328 * @section: 329 * properties 330 * 331 * @title: 332 * Driver properties 333 * 334 * @abstract: 335 * Controlling driver modules. 336 * 337 * @description: 338 * Driver modules can be controlled by setting and unsetting properties, 339 * using the functions @FT_Property_Set and @FT_Property_Get. This 340 * section documents the available properties, together with auxiliary 341 * macros and structures. 342 * 343 */ 344 345 346 /************************************************************************** 347 * 348 * @enum: 349 * FT_HINTING_XXX 350 * 351 * @description: 352 * A list of constants used for the @hinting-engine property to select 353 * the hinting engine for CFF, Type~1, and CID fonts. 354 * 355 * @values: 356 * FT_HINTING_FREETYPE :: 357 * Use the old FreeType hinting engine. 358 * 359 * FT_HINTING_ADOBE :: 360 * Use the hinting engine contributed by Adobe. 361 * 362 * @since: 363 * 2.9 364 * 365 */ 366 #define FT_HINTING_FREETYPE 0 367 #define FT_HINTING_ADOBE 1 368 369 /* these constants (introduced in 2.4.12) are deprecated */ 370 #define FT_CFF_HINTING_FREETYPE FT_HINTING_FREETYPE 371 #define FT_CFF_HINTING_ADOBE FT_HINTING_ADOBE 372 373 374 /************************************************************************** 375 * 376 * @property: 377 * hinting-engine 378 * 379 * @description: 380 * Thanks to Adobe, which contributed a new hinting (and parsing) engine, 381 * an application can select between 'freetype' and 'adobe' if compiled 382 * with `CFF_CONFIG_OPTION_OLD_ENGINE`. If this configuration macro 383 * isn't defined, 'hinting-engine' does nothing. 384 * 385 * The same holds for the Type~1 and CID modules if compiled with 386 * `T1_CONFIG_OPTION_OLD_ENGINE`. 387 * 388 * For the 'cff' module, the default engine is 'adobe'. For both the 389 * 'type1' and 't1cid' modules, the default engine is 'adobe', too. 390 * 391 * @note: 392 * This property can be used with @FT_Property_Get also. 393 * 394 * This property can be set via the `FREETYPE_PROPERTIES` environment 395 * variable (using values 'adobe' or 'freetype'). 396 * 397 * @example: 398 * The following example code demonstrates how to select Adobe's hinting 399 * engine for the 'cff' module (omitting the error handling). 400 * 401 * ``` 402 * FT_Library library; 403 * FT_UInt hinting_engine = FT_HINTING_ADOBE; 404 * 405 * 406 * FT_Init_FreeType( &library ); 407 * 408 * FT_Property_Set( library, "cff", 409 * "hinting-engine", &hinting_engine ); 410 * ``` 411 * 412 * @since: 413 * 2.4.12 (for 'cff' module) 414 * 415 * 2.9 (for 'type1' and 't1cid' modules) 416 * 417 */ 418 419 420 /************************************************************************** 421 * 422 * @property: 423 * no-stem-darkening 424 * 425 * @description: 426 * All glyphs that pass through the auto-hinter will be emboldened unless 427 * this property is set to TRUE. The same is true for the CFF, Type~1, 428 * and CID font modules if the 'Adobe' engine is selected (which is the 429 * default). 430 * 431 * Stem darkening emboldens glyphs at smaller sizes to make them more 432 * readable on common low-DPI screens when using linear alpha blending 433 * and gamma correction, see @FT_Render_Glyph. When not using linear 434 * alpha blending and gamma correction, glyphs will appear heavy and 435 * fuzzy! 436 * 437 * Gamma correction essentially lightens fonts since shades of grey are 438 * shifted to higher pixel values (=~higher brightness) to match the 439 * original intention to the reality of our screens. The side-effect is 440 * that glyphs 'thin out'. Mac OS~X and Adobe's proprietary font 441 * rendering library implement a counter-measure: stem darkening at 442 * smaller sizes where shades of gray dominate. By emboldening a glyph 443 * slightly in relation to its pixel size, individual pixels get higher 444 * coverage of filled-in outlines and are therefore 'blacker'. This 445 * counteracts the 'thinning out' of glyphs, making text remain readable 446 * at smaller sizes. 447 * 448 * For the auto-hinter, stem-darkening is experimental currently and thus 449 * switched off by default (this is, `no-stem-darkening` is set to TRUE 450 * by default). Total consistency with the CFF driver is not achieved 451 * right now because the emboldening method differs and glyphs must be 452 * scaled down on the Y-axis to keep outline points inside their 453 * precomputed blue zones. The smaller the size (especially 9ppem and 454 * down), the higher the loss of emboldening versus the CFF driver. 455 * 456 * Note that stem darkening is never applied if @FT_LOAD_NO_SCALE is set. 457 * 458 * @note: 459 * This property can be used with @FT_Property_Get also. 460 * 461 * This property can be set via the `FREETYPE_PROPERTIES` environment 462 * variable (using values 1 and 0 for 'on' and 'off', respectively). It 463 * can also be set per face using @FT_Face_Properties with 464 * @FT_PARAM_TAG_STEM_DARKENING. 465 * 466 * @example: 467 * ``` 468 * FT_Library library; 469 * FT_Bool no_stem_darkening = TRUE; 470 * 471 * 472 * FT_Init_FreeType( &library ); 473 * 474 * FT_Property_Set( library, "cff", 475 * "no-stem-darkening", &no_stem_darkening ); 476 * ``` 477 * 478 * @since: 479 * 2.4.12 (for 'cff' module) 480 * 481 * 2.6.2 (for 'autofitter' module) 482 * 483 * 2.9 (for 'type1' and 't1cid' modules) 484 * 485 */ 486 487 488 /************************************************************************** 489 * 490 * @property: 491 * darkening-parameters 492 * 493 * @description: 494 * By default, the Adobe hinting engine, as used by the CFF, Type~1, and 495 * CID font drivers, darkens stems as follows (if the `no-stem-darkening` 496 * property isn't set): 497 * 498 * ``` 499 * stem width <= 0.5px: darkening amount = 0.4px 500 * stem width = 1px: darkening amount = 0.275px 501 * stem width = 1.667px: darkening amount = 0.275px 502 * stem width >= 2.333px: darkening amount = 0px 503 * ``` 504 * 505 * and piecewise linear in-between. At configuration time, these four 506 * control points can be set with the macro 507 * `CFF_CONFIG_OPTION_DARKENING_PARAMETERS`; the CFF, Type~1, and CID 508 * drivers share these values. At runtime, the control points can be 509 * changed using the `darkening-parameters` property (see the example 510 * below that demonstrates this for the Type~1 driver). 511 * 512 * The x~values give the stem width, and the y~values the darkening 513 * amount. The unit is 1000th of pixels. All coordinate values must be 514 * positive; the x~values must be monotonically increasing; the y~values 515 * must be monotonically decreasing and smaller than or equal to 500 516 * (corresponding to half a pixel); the slope of each linear piece must 517 * be shallower than -1 (e.g., -.4). 518 * 519 * The auto-hinter provides this property, too, as an experimental 520 * feature. See @no-stem-darkening for more. 521 * 522 * @note: 523 * This property can be used with @FT_Property_Get also. 524 * 525 * This property can be set via the `FREETYPE_PROPERTIES` environment 526 * variable, using eight comma-separated integers without spaces. Here 527 * the above example, using `\` to break the line for readability. 528 * 529 * ``` 530 * FREETYPE_PROPERTIES=\ 531 * type1:darkening-parameters=500,300,1000,200,1500,100,2000,0 532 * ``` 533 * 534 * @example: 535 * ``` 536 * FT_Library library; 537 * FT_Int darken_params[8] = { 500, 300, // x1, y1 538 * 1000, 200, // x2, y2 539 * 1500, 100, // x3, y3 540 * 2000, 0 }; // x4, y4 541 * 542 * 543 * FT_Init_FreeType( &library ); 544 * 545 * FT_Property_Set( library, "type1", 546 * "darkening-parameters", darken_params ); 547 * ``` 548 * 549 * @since: 550 * 2.5.1 (for 'cff' module) 551 * 552 * 2.6.2 (for 'autofitter' module) 553 * 554 * 2.9 (for 'type1' and 't1cid' modules) 555 * 556 */ 557 558 559 /************************************************************************** 560 * 561 * @property: 562 * random-seed 563 * 564 * @description: 565 * By default, the seed value for the CFF 'random' operator and the 566 * similar '0 28 callothersubr pop' command for the Type~1 and CID 567 * drivers is set to a random value. However, mainly for debugging 568 * purposes, it is often necessary to use a known value as a seed so that 569 * the pseudo-random number sequences generated by 'random' are 570 * repeatable. 571 * 572 * The `random-seed` property does that. Its argument is a signed 32bit 573 * integer; if the value is zero or negative, the seed given by the 574 * `intitialRandomSeed` private DICT operator in a CFF file gets used (or 575 * a default value if there is no such operator). If the value is 576 * positive, use it instead of `initialRandomSeed`, which is consequently 577 * ignored. 578 * 579 * @note: 580 * This property can be set via the `FREETYPE_PROPERTIES` environment 581 * variable. It can also be set per face using @FT_Face_Properties with 582 * @FT_PARAM_TAG_RANDOM_SEED. 583 * 584 * @since: 585 * 2.8 (for 'cff' module) 586 * 587 * 2.9 (for 'type1' and 't1cid' modules) 588 * 589 */ 590 591 592 /************************************************************************** 593 * 594 * @property: 595 * no-long-family-names 596 * 597 * @description: 598 * If `PCF_CONFIG_OPTION_LONG_FAMILY_NAMES` is active while compiling 599 * FreeType, the PCF driver constructs long family names. 600 * 601 * There are many PCF fonts just called 'Fixed' which look completely 602 * different, and which have nothing to do with each other. When 603 * selecting 'Fixed' in KDE or Gnome one gets results that appear rather 604 * random, the style changes often if one changes the size and one cannot 605 * select some fonts at all. The improve this situation, the PCF module 606 * prepends the foundry name (plus a space) to the family name. It also 607 * checks whether there are 'wide' characters; all put together, family 608 * names like 'Sony Fixed' or 'Misc Fixed Wide' are constructed. 609 * 610 * If `no-long-family-names` is set, this feature gets switched off. 611 * 612 * @note: 613 * This property can be used with @FT_Property_Get also. 614 * 615 * This property can be set via the `FREETYPE_PROPERTIES` environment 616 * variable (using values 1 and 0 for 'on' and 'off', respectively). 617 * 618 * @example: 619 * ``` 620 * FT_Library library; 621 * FT_Bool no_long_family_names = TRUE; 622 * 623 * 624 * FT_Init_FreeType( &library ); 625 * 626 * FT_Property_Set( library, "pcf", 627 * "no-long-family-names", 628 * &no_long_family_names ); 629 * ``` 630 * 631 * @since: 632 * 2.8 633 */ 634 635 636 /************************************************************************** 637 * 638 * @enum: 639 * TT_INTERPRETER_VERSION_XXX 640 * 641 * @description: 642 * A list of constants used for the @interpreter-version property to 643 * select the hinting engine for Truetype fonts. 644 * 645 * The numeric value in the constant names represents the version number 646 * as returned by the 'GETINFO' bytecode instruction. 647 * 648 * @values: 649 * TT_INTERPRETER_VERSION_35 :: 650 * Version~35 corresponds to MS rasterizer v.1.7 as used e.g. in 651 * Windows~98; only grayscale and B/W rasterizing is supported. 652 * 653 * TT_INTERPRETER_VERSION_38 :: 654 * Version~38 corresponds to MS rasterizer v.1.9; it is roughly 655 * equivalent to the hinting provided by DirectWrite ClearType (as can 656 * be found, for example, in the Internet Explorer~9 running on 657 * Windows~7). It is used in FreeType to select the 'Infinality' 658 * subpixel hinting code. The code may be removed in a future version. 659 * 660 * TT_INTERPRETER_VERSION_40 :: 661 * Version~40 corresponds to MS rasterizer v.2.1; it is roughly 662 * equivalent to the hinting provided by DirectWrite ClearType (as can 663 * be found, for example, in Microsoft's Edge Browser on Windows~10). 664 * It is used in FreeType to select the 'minimal' subpixel hinting 665 * code, a stripped-down and higher performance version of the 666 * 'Infinality' code. 667 * 668 * @note: 669 * This property controls the behaviour of the bytecode interpreter and 670 * thus how outlines get hinted. It does **not** control how glyph get 671 * rasterized! In particular, it does not control subpixel color 672 * filtering. 673 * 674 * If FreeType has not been compiled with the configuration option 675 * `TT_CONFIG_OPTION_SUBPIXEL_HINTING`, selecting version~38 or~40 causes 676 * an `FT_Err_Unimplemented_Feature` error. 677 * 678 * Depending on the graphics framework, Microsoft uses different bytecode 679 * and rendering engines. As a consequence, the version numbers returned 680 * by a call to the 'GETINFO' bytecode instruction are more convoluted 681 * than desired. 682 * 683 * Here are two tables that try to shed some light on the possible values 684 * for the MS rasterizer engine, together with the additional features 685 * introduced by it. 686 * 687 * ``` 688 * GETINFO framework version feature 689 * ------------------------------------------------------------------- 690 * 3 GDI (Win 3.1), v1.0 16-bit, first version 691 * TrueImage 692 * 33 GDI (Win NT 3.1), v1.5 32-bit 693 * HP Laserjet 694 * 34 GDI (Win 95) v1.6 font smoothing, 695 * new SCANTYPE opcode 696 * 35 GDI (Win 98/2000) v1.7 (UN)SCALED_COMPONENT_OFFSET 697 * bits in composite glyphs 698 * 36 MGDI (Win CE 2) v1.6+ classic ClearType 699 * 37 GDI (XP and later), v1.8 ClearType 700 * GDI+ old (before Vista) 701 * 38 GDI+ old (Vista, Win 7), v1.9 subpixel ClearType, 702 * WPF Y-direction ClearType, 703 * additional error checking 704 * 39 DWrite (before Win 8) v2.0 subpixel ClearType flags 705 * in GETINFO opcode, 706 * bug fixes 707 * 40 GDI+ (after Win 7), v2.1 Y-direction ClearType flag 708 * DWrite (Win 8) in GETINFO opcode, 709 * Gray ClearType 710 * ``` 711 * 712 * The 'version' field gives a rough orientation only, since some 713 * applications provided certain features much earlier (as an example, 714 * Microsoft Reader used subpixel and Y-direction ClearType already in 715 * Windows 2000). Similarly, updates to a given framework might include 716 * improved hinting support. 717 * 718 * ``` 719 * version sampling rendering comment 720 * x y x y 721 * -------------------------------------------------------------- 722 * v1.0 normal normal B/W B/W bi-level 723 * v1.6 high high gray gray grayscale 724 * v1.8 high normal color-filter B/W (GDI) ClearType 725 * v1.9 high high color-filter gray Color ClearType 726 * v2.1 high normal gray B/W Gray ClearType 727 * v2.1 high high gray gray Gray ClearType 728 * ``` 729 * 730 * Color and Gray ClearType are the two available variants of 731 * 'Y-direction ClearType', meaning grayscale rasterization along the 732 * Y-direction; the name used in the TrueType specification for this 733 * feature is 'symmetric smoothing'. 'Classic ClearType' is the original 734 * algorithm used before introducing a modified version in Win~XP. 735 * Another name for v1.6's grayscale rendering is 'font smoothing', and 736 * 'Color ClearType' is sometimes also called 'DWrite ClearType'. To 737 * differentiate between today's Color ClearType and the earlier 738 * ClearType variant with B/W rendering along the vertical axis, the 739 * latter is sometimes called 'GDI ClearType'. 740 * 741 * 'Normal' and 'high' sampling describe the (virtual) resolution to 742 * access the rasterized outline after the hinting process. 'Normal' 743 * means 1 sample per grid line (i.e., B/W). In the current Microsoft 744 * implementation, 'high' means an extra virtual resolution of 16x16 (or 745 * 16x1) grid lines per pixel for bytecode instructions like 'MIRP'. 746 * After hinting, these 16 grid lines are mapped to 6x5 (or 6x1) grid 747 * lines for color filtering if Color ClearType is activated. 748 * 749 * Note that 'Gray ClearType' is essentially the same as v1.6's grayscale 750 * rendering. However, the GETINFO instruction handles it differently: 751 * v1.6 returns bit~12 (hinting for grayscale), while v2.1 returns 752 * bits~13 (hinting for ClearType), 18 (symmetrical smoothing), and~19 753 * (Gray ClearType). Also, this mode respects bits 2 and~3 for the 754 * version~1 gasp table exclusively (like Color ClearType), while v1.6 755 * only respects the values of version~0 (bits 0 and~1). 756 * 757 * Keep in mind that the features of the above interpreter versions might 758 * not map exactly to FreeType features or behavior because it is a 759 * fundamentally different library with different internals. 760 * 761 */ 762 #define TT_INTERPRETER_VERSION_35 35 763 #define TT_INTERPRETER_VERSION_38 38 764 #define TT_INTERPRETER_VERSION_40 40 765 766 767 /************************************************************************** 768 * 769 * @property: 770 * interpreter-version 771 * 772 * @description: 773 * Currently, three versions are available, two representing the bytecode 774 * interpreter with subpixel hinting support (old 'Infinality' code and 775 * new stripped-down and higher performance 'minimal' code) and one 776 * without, respectively. The default is subpixel support if 777 * `TT_CONFIG_OPTION_SUBPIXEL_HINTING` is defined, and no subpixel 778 * support otherwise (since it isn't available then). 779 * 780 * If subpixel hinting is on, many TrueType bytecode instructions behave 781 * differently compared to B/W or grayscale rendering (except if 'native 782 * ClearType' is selected by the font). Microsoft's main idea is to 783 * render at a much increased horizontal resolution, then sampling down 784 * the created output to subpixel precision. However, many older fonts 785 * are not suited to this and must be specially taken care of by applying 786 * (hardcoded) tweaks in Microsoft's interpreter. 787 * 788 * Details on subpixel hinting and some of the necessary tweaks can be 789 * found in Greg Hitchcock's whitepaper at 790 * 'https://www.microsoft.com/typography/cleartype/truetypecleartype.aspx'. 791 * Note that FreeType currently doesn't really 'subpixel hint' (6x1, 6x2, 792 * or 6x5 supersampling) like discussed in the paper. Depending on the 793 * chosen interpreter, it simply ignores instructions on vertical stems 794 * to arrive at very similar results. 795 * 796 * @note: 797 * This property can be used with @FT_Property_Get also. 798 * 799 * This property can be set via the `FREETYPE_PROPERTIES` environment 800 * variable (using values '35', '38', or '40'). 801 * 802 * @example: 803 * The following example code demonstrates how to deactivate subpixel 804 * hinting (omitting the error handling). 805 * 806 * ``` 807 * FT_Library library; 808 * FT_Face face; 809 * FT_UInt interpreter_version = TT_INTERPRETER_VERSION_35; 810 * 811 * 812 * FT_Init_FreeType( &library ); 813 * 814 * FT_Property_Set( library, "truetype", 815 * "interpreter-version", 816 * &interpreter_version ); 817 * ``` 818 * 819 * @since: 820 * 2.5 821 */ 822 823 /************************************************************************** 824 * 825 * @property: 826 * svg-hooks 827 * 828 * @description: 829 * Set up the interface between FreeType and an extern SVG rendering 830 * library like 'librsvg'. All details on the function hooks can be 831 * found in section @svg_fonts. 832 * 833 * @example: 834 * The following example code expects that the four hook functions 835 * `svg_*` are defined elsewhere. Error handling is omitted, too. 836 * 837 * ``` 838 * FT_Library library; 839 * SVG_RendererHooks hooks = { 840 * (SVG_Lib_Init_Func)svg_init, 841 * (SVG_Lib_Free_Func)svg_free, 842 * (SVG_Lib_Render_Func)svg_render, 843 * (SVG_Lib_Preset_Slot_Func)svg_preset_slot }; 844 * 845 * 846 * FT_Init_FreeType( &library ); 847 * 848 * FT_Property_Set( library, "ot-svg", 849 * "svg-hooks", &hooks ); 850 * ``` 851 * 852 * @since: 853 * 2.12 854 */ 855 856 857 /************************************************************************** 858 * 859 * @property: 860 * glyph-to-script-map 861 * 862 * @description: 863 * **Experimental only** 864 * 865 * The auto-hinter provides various script modules to hint glyphs. 866 * Examples of supported scripts are Latin or CJK. Before a glyph is 867 * auto-hinted, the Unicode character map of the font gets examined, and 868 * the script is then determined based on Unicode character ranges, see 869 * below. 870 * 871 * OpenType fonts, however, often provide much more glyphs than character 872 * codes (small caps, superscripts, ligatures, swashes, etc.), to be 873 * controlled by so-called 'features'. Handling OpenType features can be 874 * quite complicated and thus needs a separate library on top of 875 * FreeType. 876 * 877 * The mapping between glyph indices and scripts (in the auto-hinter 878 * sense, see the @FT_AUTOHINTER_SCRIPT_XXX values) is stored as an array 879 * with `num_glyphs` elements, as found in the font's @FT_Face structure. 880 * The `glyph-to-script-map` property returns a pointer to this array, 881 * which can be modified as needed. Note that the modification should 882 * happen before the first glyph gets processed by the auto-hinter so 883 * that the global analysis of the font shapes actually uses the modified 884 * mapping. 885 * 886 * @example: 887 * The following example code demonstrates how to access it (omitting the 888 * error handling). 889 * 890 * ``` 891 * FT_Library library; 892 * FT_Face face; 893 * FT_Prop_GlyphToScriptMap prop; 894 * 895 * 896 * FT_Init_FreeType( &library ); 897 * FT_New_Face( library, "foo.ttf", 0, &face ); 898 * 899 * prop.face = face; 900 * 901 * FT_Property_Get( library, "autofitter", 902 * "glyph-to-script-map", &prop ); 903 * 904 * // adjust `prop.map' as needed right here 905 * 906 * FT_Load_Glyph( face, ..., FT_LOAD_FORCE_AUTOHINT ); 907 * ``` 908 * 909 * @since: 910 * 2.4.11 911 * 912 */ 913 914 915 /************************************************************************** 916 * 917 * @enum: 918 * FT_AUTOHINTER_SCRIPT_XXX 919 * 920 * @description: 921 * **Experimental only** 922 * 923 * A list of constants used for the @glyph-to-script-map property to 924 * specify the script submodule the auto-hinter should use for hinting a 925 * particular glyph. 926 * 927 * @values: 928 * FT_AUTOHINTER_SCRIPT_NONE :: 929 * Don't auto-hint this glyph. 930 * 931 * FT_AUTOHINTER_SCRIPT_LATIN :: 932 * Apply the latin auto-hinter. For the auto-hinter, 'latin' is a very 933 * broad term, including Cyrillic and Greek also since characters from 934 * those scripts share the same design constraints. 935 * 936 * By default, characters from the following Unicode ranges are 937 * assigned to this submodule. 938 * 939 * ``` 940 * U+0020 - U+007F // Basic Latin (no control characters) 941 * U+00A0 - U+00FF // Latin-1 Supplement (no control characters) 942 * U+0100 - U+017F // Latin Extended-A 943 * U+0180 - U+024F // Latin Extended-B 944 * U+0250 - U+02AF // IPA Extensions 945 * U+02B0 - U+02FF // Spacing Modifier Letters 946 * U+0300 - U+036F // Combining Diacritical Marks 947 * U+0370 - U+03FF // Greek and Coptic 948 * U+0400 - U+04FF // Cyrillic 949 * U+0500 - U+052F // Cyrillic Supplement 950 * U+1D00 - U+1D7F // Phonetic Extensions 951 * U+1D80 - U+1DBF // Phonetic Extensions Supplement 952 * U+1DC0 - U+1DFF // Combining Diacritical Marks Supplement 953 * U+1E00 - U+1EFF // Latin Extended Additional 954 * U+1F00 - U+1FFF // Greek Extended 955 * U+2000 - U+206F // General Punctuation 956 * U+2070 - U+209F // Superscripts and Subscripts 957 * U+20A0 - U+20CF // Currency Symbols 958 * U+2150 - U+218F // Number Forms 959 * U+2460 - U+24FF // Enclosed Alphanumerics 960 * U+2C60 - U+2C7F // Latin Extended-C 961 * U+2DE0 - U+2DFF // Cyrillic Extended-A 962 * U+2E00 - U+2E7F // Supplemental Punctuation 963 * U+A640 - U+A69F // Cyrillic Extended-B 964 * U+A720 - U+A7FF // Latin Extended-D 965 * U+FB00 - U+FB06 // Alphab. Present. Forms (Latin Ligatures) 966 * U+1D400 - U+1D7FF // Mathematical Alphanumeric Symbols 967 * U+1F100 - U+1F1FF // Enclosed Alphanumeric Supplement 968 * ``` 969 * 970 * FT_AUTOHINTER_SCRIPT_CJK :: 971 * Apply the CJK auto-hinter, covering Chinese, Japanese, Korean, old 972 * Vietnamese, and some other scripts. 973 * 974 * By default, characters from the following Unicode ranges are 975 * assigned to this submodule. 976 * 977 * ``` 978 * U+1100 - U+11FF // Hangul Jamo 979 * U+2E80 - U+2EFF // CJK Radicals Supplement 980 * U+2F00 - U+2FDF // Kangxi Radicals 981 * U+2FF0 - U+2FFF // Ideographic Description Characters 982 * U+3000 - U+303F // CJK Symbols and Punctuation 983 * U+3040 - U+309F // Hiragana 984 * U+30A0 - U+30FF // Katakana 985 * U+3100 - U+312F // Bopomofo 986 * U+3130 - U+318F // Hangul Compatibility Jamo 987 * U+3190 - U+319F // Kanbun 988 * U+31A0 - U+31BF // Bopomofo Extended 989 * U+31C0 - U+31EF // CJK Strokes 990 * U+31F0 - U+31FF // Katakana Phonetic Extensions 991 * U+3200 - U+32FF // Enclosed CJK Letters and Months 992 * U+3300 - U+33FF // CJK Compatibility 993 * U+3400 - U+4DBF // CJK Unified Ideographs Extension A 994 * U+4DC0 - U+4DFF // Yijing Hexagram Symbols 995 * U+4E00 - U+9FFF // CJK Unified Ideographs 996 * U+A960 - U+A97F // Hangul Jamo Extended-A 997 * U+AC00 - U+D7AF // Hangul Syllables 998 * U+D7B0 - U+D7FF // Hangul Jamo Extended-B 999 * U+F900 - U+FAFF // CJK Compatibility Ideographs 1000 * U+FE10 - U+FE1F // Vertical forms 1001 * U+FE30 - U+FE4F // CJK Compatibility Forms 1002 * U+FF00 - U+FFEF // Halfwidth and Fullwidth Forms 1003 * U+1B000 - U+1B0FF // Kana Supplement 1004 * U+1D300 - U+1D35F // Tai Xuan Hing Symbols 1005 * U+1F200 - U+1F2FF // Enclosed Ideographic Supplement 1006 * U+20000 - U+2A6DF // CJK Unified Ideographs Extension B 1007 * U+2A700 - U+2B73F // CJK Unified Ideographs Extension C 1008 * U+2B740 - U+2B81F // CJK Unified Ideographs Extension D 1009 * U+2F800 - U+2FA1F // CJK Compatibility Ideographs Supplement 1010 * ``` 1011 * 1012 * FT_AUTOHINTER_SCRIPT_INDIC :: 1013 * Apply the indic auto-hinter, covering all major scripts from the 1014 * Indian sub-continent and some other related scripts like Thai, Lao, 1015 * or Tibetan. 1016 * 1017 * By default, characters from the following Unicode ranges are 1018 * assigned to this submodule. 1019 * 1020 * ``` 1021 * U+0900 - U+0DFF // Indic Range 1022 * U+0F00 - U+0FFF // Tibetan 1023 * U+1900 - U+194F // Limbu 1024 * U+1B80 - U+1BBF // Sundanese 1025 * U+A800 - U+A82F // Syloti Nagri 1026 * U+ABC0 - U+ABFF // Meetei Mayek 1027 * U+11800 - U+118DF // Sharada 1028 * ``` 1029 * 1030 * Note that currently Indic support is rudimentary only, missing blue 1031 * zone support. 1032 * 1033 * @since: 1034 * 2.4.11 1035 * 1036 */ 1037 #define FT_AUTOHINTER_SCRIPT_NONE 0 1038 #define FT_AUTOHINTER_SCRIPT_LATIN 1 1039 #define FT_AUTOHINTER_SCRIPT_CJK 2 1040 #define FT_AUTOHINTER_SCRIPT_INDIC 3 1041 1042 1043 /************************************************************************** 1044 * 1045 * @struct: 1046 * FT_Prop_GlyphToScriptMap 1047 * 1048 * @description: 1049 * **Experimental only** 1050 * 1051 * The data exchange structure for the @glyph-to-script-map property. 1052 * 1053 * @since: 1054 * 2.4.11 1055 * 1056 */ 1057 typedef struct FT_Prop_GlyphToScriptMap_ 1058 { 1059 FT_Face face; 1060 FT_UShort* map; 1061 1062 } FT_Prop_GlyphToScriptMap; 1063 1064 1065 /************************************************************************** 1066 * 1067 * @property: 1068 * fallback-script 1069 * 1070 * @description: 1071 * **Experimental only** 1072 * 1073 * If no auto-hinter script module can be assigned to a glyph, a fallback 1074 * script gets assigned to it (see also the @glyph-to-script-map 1075 * property). By default, this is @FT_AUTOHINTER_SCRIPT_CJK. Using the 1076 * `fallback-script` property, this fallback value can be changed. 1077 * 1078 * @note: 1079 * This property can be used with @FT_Property_Get also. 1080 * 1081 * It's important to use the right timing for changing this value: The 1082 * creation of the glyph-to-script map that eventually uses the fallback 1083 * script value gets triggered either by setting or reading a 1084 * face-specific property like @glyph-to-script-map, or by auto-hinting 1085 * any glyph from that face. In particular, if you have already created 1086 * an @FT_Face structure but not loaded any glyph (using the 1087 * auto-hinter), a change of the fallback script will affect this face. 1088 * 1089 * @example: 1090 * ``` 1091 * FT_Library library; 1092 * FT_UInt fallback_script = FT_AUTOHINTER_SCRIPT_NONE; 1093 * 1094 * 1095 * FT_Init_FreeType( &library ); 1096 * 1097 * FT_Property_Set( library, "autofitter", 1098 * "fallback-script", &fallback_script ); 1099 * ``` 1100 * 1101 * @since: 1102 * 2.4.11 1103 * 1104 */ 1105 1106 1107 /************************************************************************** 1108 * 1109 * @property: 1110 * default-script 1111 * 1112 * @description: 1113 * **Experimental only** 1114 * 1115 * If FreeType gets compiled with `FT_CONFIG_OPTION_USE_HARFBUZZ` to make 1116 * the HarfBuzz library access OpenType features for getting better glyph 1117 * coverages, this property sets the (auto-fitter) script to be used for 1118 * the default (OpenType) script data of a font's GSUB table. Features 1119 * for the default script are intended for all scripts not explicitly 1120 * handled in GSUB; an example is a 'dlig' feature, containing the 1121 * combination of the characters 'T', 'E', and 'L' to form a 'TEL' 1122 * ligature. 1123 * 1124 * By default, this is @FT_AUTOHINTER_SCRIPT_LATIN. Using the 1125 * `default-script` property, this default value can be changed. 1126 * 1127 * @note: 1128 * This property can be used with @FT_Property_Get also. 1129 * 1130 * It's important to use the right timing for changing this value: The 1131 * creation of the glyph-to-script map that eventually uses the default 1132 * script value gets triggered either by setting or reading a 1133 * face-specific property like @glyph-to-script-map, or by auto-hinting 1134 * any glyph from that face. In particular, if you have already created 1135 * an @FT_Face structure but not loaded any glyph (using the 1136 * auto-hinter), a change of the default script will affect this face. 1137 * 1138 * @example: 1139 * ``` 1140 * FT_Library library; 1141 * FT_UInt default_script = FT_AUTOHINTER_SCRIPT_NONE; 1142 * 1143 * 1144 * FT_Init_FreeType( &library ); 1145 * 1146 * FT_Property_Set( library, "autofitter", 1147 * "default-script", &default_script ); 1148 * ``` 1149 * 1150 * @since: 1151 * 2.5.3 1152 * 1153 */ 1154 1155 1156 /************************************************************************** 1157 * 1158 * @property: 1159 * increase-x-height 1160 * 1161 * @description: 1162 * For ppem values in the range 6~<= ppem <= `increase-x-height`, round 1163 * up the font's x~height much more often than normally. If the value is 1164 * set to~0, which is the default, this feature is switched off. Use 1165 * this property to improve the legibility of small font sizes if 1166 * necessary. 1167 * 1168 * @note: 1169 * This property can be used with @FT_Property_Get also. 1170 * 1171 * Set this value right after calling @FT_Set_Char_Size, but before 1172 * loading any glyph (using the auto-hinter). 1173 * 1174 * @example: 1175 * ``` 1176 * FT_Library library; 1177 * FT_Face face; 1178 * FT_Prop_IncreaseXHeight prop; 1179 * 1180 * 1181 * FT_Init_FreeType( &library ); 1182 * FT_New_Face( library, "foo.ttf", 0, &face ); 1183 * FT_Set_Char_Size( face, 10 * 64, 0, 72, 0 ); 1184 * 1185 * prop.face = face; 1186 * prop.limit = 14; 1187 * 1188 * FT_Property_Set( library, "autofitter", 1189 * "increase-x-height", &prop ); 1190 * ``` 1191 * 1192 * @since: 1193 * 2.4.11 1194 * 1195 */ 1196 1197 1198 /************************************************************************** 1199 * 1200 * @struct: 1201 * FT_Prop_IncreaseXHeight 1202 * 1203 * @description: 1204 * The data exchange structure for the @increase-x-height property. 1205 * 1206 */ 1207 typedef struct FT_Prop_IncreaseXHeight_ 1208 { 1209 FT_Face face; 1210 FT_UInt limit; 1211 1212 } FT_Prop_IncreaseXHeight; 1213 1214 1215 /************************************************************************** 1216 * 1217 * @property: 1218 * warping 1219 * 1220 * @description: 1221 * **Obsolete** 1222 * 1223 * This property was always experimental and probably never worked 1224 * correctly. It was entirely removed from the FreeType~2 sources. This 1225 * entry is only here for historical reference. 1226 * 1227 * Warping only worked in 'normal' auto-hinting mode replacing it. The 1228 * idea of the code was to slightly scale and shift a glyph along the 1229 * non-hinted dimension (which is usually the horizontal axis) so that as 1230 * much of its segments were aligned (more or less) to the grid. To find 1231 * out a glyph's optimal scaling and shifting value, various parameter 1232 * combinations were tried and scored. 1233 * 1234 * @since: 1235 * 2.6 1236 * 1237 */ 1238 1239 1240 /* */ 1241 1242 1243 FT_END_HEADER 1244 1245 1246 #endif /* FTDRIVER_H_ */ 1247 1248 1249 /* END */ 1250