1/****************************************************************************
2 *
3 * ttinterp.h
4 *
5 * TrueType bytecode interpreter (specification).
6 *
7 * Copyright (C) 1996-2019 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 TTINTERP_H_
20#define TTINTERP_H_
21
22#include <ft2build.h>
23#include "ttobjs.h"
24
25
26FT_BEGIN_HEADER
27
28
29 /**************************************************************************
30 *
31 * Rounding mode constants.
32 */
33#define TT_Round_Off 5
34#define TT_Round_To_Half_Grid 0
35#define TT_Round_To_Grid 1
36#define TT_Round_To_Double_Grid 2
37#define TT_Round_Up_To_Grid 4
38#define TT_Round_Down_To_Grid 3
39#define TT_Round_Super 6
40#define TT_Round_Super_45 7
41
42
43 /**************************************************************************
44 *
45 * Function types used by the interpreter, depending on various modes
46 * (e.g. the rounding mode, whether to render a vertical or horizontal
47 * line etc).
48 *
49 */
50
51 /* Rounding function */
52 typedef FT_F26Dot6
53 (*TT_Round_Func)( TT_ExecContext exc,
54 FT_F26Dot6 distance,
55 FT_F26Dot6 compensation );
56
57 /* Point displacement along the freedom vector routine */
58 typedef void
59 (*TT_Move_Func)( TT_ExecContext exc,
60 TT_GlyphZone zone,
61 FT_UShort point,
62 FT_F26Dot6 distance );
63
64 /* Distance projection along one of the projection vectors */
65 typedef FT_F26Dot6
66 (*TT_Project_Func)( TT_ExecContext exc,
67 FT_Pos dx,
68 FT_Pos dy );
69
70 /* getting current ppem. Take care of non-square pixels if necessary */
71 typedef FT_Long
72 (*TT_Cur_Ppem_Func)( TT_ExecContext exc );
73
74 /* reading a cvt value. Take care of non-square pixels if necessary */
75 typedef FT_F26Dot6
76 (*TT_Get_CVT_Func)( TT_ExecContext exc,
77 FT_ULong idx );
78
79 /* setting or moving a cvt value. Take care of non-square pixels */
80 /* if necessary */
81 typedef void
82 (*TT_Set_CVT_Func)( TT_ExecContext exc,
83 FT_ULong idx,
84 FT_F26Dot6 value );
85
86
87 /**************************************************************************
88 *
89 * This structure defines a call record, used to manage function calls.
90 */
91 typedef struct TT_CallRec_
92 {
93 FT_Int Caller_Range;
94 FT_Long Caller_IP;
95 FT_Long Cur_Count;
96
97 TT_DefRecord *Def; /* either FDEF or IDEF */
98
99 } TT_CallRec, *TT_CallStack;
100
101
102#ifdef TT_SUPPORT_SUBPIXEL_HINTING_INFINALITY
103
104 /**************************************************************************
105 *
106 * These structures define rules used to tweak subpixel hinting for
107 * various fonts. "", 0, "", NULL value indicates to match any value.
108 */
109
110#define SPH_MAX_NAME_SIZE 32
111#define SPH_MAX_CLASS_MEMBERS 100
112
113 typedef struct SPH_TweakRule_
114 {
115 const char family[SPH_MAX_NAME_SIZE];
116 const FT_UInt ppem;
117 const char style[SPH_MAX_NAME_SIZE];
118 const FT_ULong glyph;
119
120 } SPH_TweakRule;
121
122
123 typedef struct SPH_ScaleRule_
124 {
125 const char family[SPH_MAX_NAME_SIZE];
126 const FT_UInt ppem;
127 const char style[SPH_MAX_NAME_SIZE];
128 const FT_ULong glyph;
129 const FT_ULong scale;
130
131 } SPH_ScaleRule;
132
133
134 typedef struct SPH_Font_Class_
135 {
136 const char name[SPH_MAX_NAME_SIZE];
137 const char member[SPH_MAX_CLASS_MEMBERS][SPH_MAX_NAME_SIZE];
138
139 } SPH_Font_Class;
140
141#endif /* TT_SUPPORT_SUBPIXEL_HINTING_INFINALITY */
142
143
144 /**************************************************************************
145 *
146 * The main structure for the interpreter which collects all necessary
147 * variables and states.
148 */
149 typedef struct TT_ExecContextRec_
150 {
151 TT_Face face;
152 TT_Size size;
153 FT_Memory memory;
154
155 /* instructions state */
156
157 FT_Error error; /* last execution error */
158
159 FT_Long top; /* top of exec. stack */
160
161 FT_Long stackSize; /* size of exec. stack */
162 FT_Long* stack; /* current exec. stack */
163
164 FT_Long args;
165 FT_Long new_top; /* new top after exec. */
166
167 TT_GlyphZoneRec zp0, /* zone records */
168 zp1,
169 zp2,
170 pts,
171 twilight;
172
173 FT_Long pointSize; /* in 26.6 format */
174 FT_Size_Metrics metrics;
175 TT_Size_Metrics tt_metrics; /* size metrics */
176
177 TT_GraphicsState GS; /* current graphics state */
178
179 FT_Int curRange; /* current code range number */
180 FT_Byte* code; /* current code range */
181 FT_Long IP; /* current instruction pointer */
182 FT_Long codeSize; /* size of current range */
183
184 FT_Byte opcode; /* current opcode */
185 FT_Int length; /* length of current opcode */
186
187 FT_Bool step_ins; /* true if the interpreter must */
188 /* increment IP after ins. exec */
189 FT_ULong cvtSize;
190 FT_Long* cvt;
191
192 FT_UInt glyphSize; /* glyph instructions buffer size */
193 FT_Byte* glyphIns; /* glyph instructions buffer */
194
195 FT_UInt numFDefs; /* number of function defs */
196 FT_UInt maxFDefs; /* maximum number of function defs */
197 TT_DefArray FDefs; /* table of FDefs entries */
198
199 FT_UInt numIDefs; /* number of instruction defs */
200 FT_UInt maxIDefs; /* maximum number of ins defs */
201 TT_DefArray IDefs; /* table of IDefs entries */
202
203 FT_UInt maxFunc; /* maximum function index */
204 FT_UInt maxIns; /* maximum instruction index */
205
206 FT_Int callTop, /* top of call stack during execution */
207 callSize; /* size of call stack */
208 TT_CallStack callStack; /* call stack */
209
210 FT_UShort maxPoints; /* capacity of this context's `pts' */
211 FT_Short maxContours; /* record, expressed in points and */
212 /* contours. */
213
214 TT_CodeRangeTable codeRangeTable; /* table of valid code ranges */
215 /* useful for the debugger */
216
217 FT_UShort storeSize; /* size of current storage */
218 FT_Long* storage; /* storage area */
219
220 FT_F26Dot6 period; /* values used for the */
221 FT_F26Dot6 phase; /* `SuperRounding' */
222 FT_F26Dot6 threshold;
223
224 FT_Bool instruction_trap; /* If `True', the interpreter will */
225 /* exit after each instruction */
226
227 TT_GraphicsState default_GS; /* graphics state resulting from */
228 /* the prep program */
229 FT_Bool is_composite; /* true if the glyph is composite */
230 FT_Bool pedantic_hinting; /* true if pedantic interpretation */
231
232 /* latest interpreter additions */
233
234 FT_Long F_dot_P; /* dot product of freedom and projection */
235 /* vectors */
236 TT_Round_Func func_round; /* current rounding function */
237
238 TT_Project_Func func_project, /* current projection function */
239 func_dualproj, /* current dual proj. function */
240 func_freeProj; /* current freedom proj. func */
241
242 TT_Move_Func func_move; /* current point move function */
243 TT_Move_Func func_move_orig; /* move original position function */
244
245 TT_Cur_Ppem_Func func_cur_ppem; /* get current proj. ppem value */
246
247 TT_Get_CVT_Func func_read_cvt; /* read a cvt entry */
248 TT_Set_CVT_Func func_write_cvt; /* write a cvt entry (in pixels) */
249 TT_Set_CVT_Func func_move_cvt; /* incr a cvt entry (in pixels) */
250
251 FT_Bool grayscale; /* bi-level hinting and */
252 /* grayscale rendering */
253
254#ifdef TT_SUPPORT_SUBPIXEL_HINTING_MINIMAL
255 /*
256 * FreeType supports ClearType-like hinting of TrueType fonts through
257 * the version 40 interpreter. This is achieved through several hacks
258 * in the base (v35) interpreter, as detailed below.
259 *
260 * ClearType is an umbrella term for several rendering techniques
261 * employed by Microsoft's various GUI and rendering toolkit
262 * implementations, most importantly: subpixel rendering for using the
263 * RGB subpixels of LCDs to approximately triple the perceived
264 * resolution on the x-axis and subpixel hinting for positioning stems
265 * on subpixel borders. TrueType programming is explicit, i.e., fonts
266 * must be programmed to take advantage of ClearType's possibilities.
267 *
268 * When ClearType was introduced, it seemed unlikely that all fonts
269 * would be reprogrammed, so Microsoft decided to implement a backward
270 * compatibility mode. It employs several simple to complicated
271 * assumptions and tricks, many of them font-dependent, that modify the
272 * interpretation of the bytecode contained in these fonts to retrofit
273 * them into a ClearType-y look. The quality of the results varies.
274 * Most (web)fonts that were released since then have come to rely on
275 * these hacks to render correctly, even some of Microsoft's flagship
276 * fonts (e.g., Calibri, Cambria, Segoe UI).
277 *
278 * FreeType's minimal subpixel hinting code (interpreter version 40)
279 * employs a small list of font-agnostic hacks loosely based on the
280 * public information available on Microsoft's compatibility mode[2].
281 * The focus is on modern (web)fonts rather than legacy fonts that were
282 * made for monochrome rendering. It will not match ClearType rendering
283 * exactly. Unlike the `Infinality' code (interpreter version 38) that
284 * came before, it will not try to toggle hacks for specific fonts for
285 * performance and complexity reasons. It will fall back to version 35
286 * behavior for tricky fonts[1] or when monochrome rendering is
287 * requested.
288 *
289 * Major hacks
290 *
291 * - Any point movement on the x axis is ignored (cf. `Direct_Move' and
292 * `Direct_Move_X'). This has the smallest code footprint and single
293 * biggest effect. The ClearType way to increase resolution is
294 * supersampling the x axis, the FreeType way is ignoring instructions
295 * on the x axis, which gives the same result in the majority of
296 * cases.
297 *
298 * - Points are not moved post-IUP (neither on the x nor on the y axis),
299 * except the x component of diagonal moves post-IUP (cf.
300 * `Direct_Move', `Direct_Move_Y', `Move_Zp2_Point'). Post-IUP
301 * changes are commonly used to `fix' pixel patterns which has little
302 * use outside monochrome rendering.
303 *
304 * - SHPIX and DELTAP don't execute unless moving a composite on the
305 * y axis or moving a previously y touched point. SHPIX additionally
306 * denies movement on the x axis (cf. `Ins_SHPIX' and `Ins_DELTAP').
307 * Both instructions are commonly used to `fix' pixel patterns for
308 * monochrome or Windows's GDI rendering but make little sense for
309 * FreeType rendering. Both can distort the outline. See [2] for
310 * details.
311 *
312 * - The hdmx table and modifications to phantom points are ignored.
313 * Bearings and advance widths remain unchanged (except rounding them
314 * outside the interpreter!), cf. `compute_glyph_metrics' and
315 * `TT_Hint_Glyph'. Letting non-native-ClearType fonts modify spacing
316 * might mess up spacing.
317 *
318 * Minor hacks
319 *
320 * - FLIPRGON, FLIPRGOFF, and FLIPPT don't execute post-IUP. This
321 * prevents dents in e.g. Arial-Regular's `D' and `G' glyphs at
322 * various sizes.
323 *
324 * (Post-IUP is the state after both IUP[x] and IUP[y] have been
325 * executed.)
326 *
327 * The best results are achieved for fonts that were from the outset
328 * designed with ClearType in mind, meaning they leave the x axis mostly
329 * alone and don't mess with the `final' outline to produce more
330 * pleasing pixel patterns. The harder the designer tried to produce
331 * very specific patterns (`superhinting') for pre-ClearType-displays,
332 * the worse the results.
333 *
334 * Microsoft defines a way to turn off backward compatibility and
335 * interpret instructions as before (called `native ClearType')[2][3].
336 * The font designer then regains full control and is responsible for
337 * making the font work correctly with ClearType without any
338 * hand-holding by the interpreter or rasterizer[4]. The v40
339 * interpreter assumes backward compatibility by default, which can be
340 * turned off the same way by executing the following in the control
341 * program (cf. `Ins_INSTCTRL').
342 *
343 * #PUSH 4,3
344 * INSTCTRL[]
345 *
346 * [1] Tricky fonts as FreeType defines them rely on the bytecode
347 * interpreter to display correctly. Hacks can interfere with them,
348 * so they get treated like native ClearType fonts (v40 with
349 * backward compatibility turned off). Cf. `TT_RunIns'.
350 *
351 * [2] Proposed by Microsoft's Greg Hitchcock in
352 * https://www.microsoft.com/typography/cleartype/truetypecleartype.aspx
353 *
354 * [3] Beat Stamm describes it in more detail:
355 * http://rastertragedy.com/RTRCh4.htm#Sec12.
356 *
357 * [4] The list of `native ClearType' fonts is small at the time of this
358 * writing; I found the following on a Windows 10 Update 1511
359 * installation: Constantia, Corbel, Sitka, Malgun Gothic, Microsoft
360 * JhengHei (Bold and UI Bold), Microsoft YaHei (Bold and UI Bold),
361 * SimSun, NSimSun, and Yu Gothic.
362 *
363 */
364
365 /* Using v40 implies subpixel hinting, unless FT_RENDER_MODE_MONO has been
366 * requested. Used to detect interpreter */
367 /* version switches. `_lean' to differentiate from the Infinality */
368 /* `subpixel_hinting', which is managed differently. */
369 FT_Bool subpixel_hinting_lean;
370
371 /* Long side of a LCD subpixel is vertical (e.g., screen is rotated). */
372 /* `_lean' to differentiate from the Infinality `vertical_lcd', which */
373 /* is managed differently. */
374 FT_Bool vertical_lcd_lean;
375
376 /* Default to backward compatibility mode in v40 interpreter. If */
377 /* this is false, it implies the interpreter is in v35 or in native */
378 /* ClearType mode. */
379 FT_Bool backward_compatibility;
380
381 /* Useful for detecting and denying post-IUP trickery that is usually */
382 /* used to fix pixel patterns (`superhinting'). */
383 FT_Bool iupx_called;
384 FT_Bool iupy_called;
385
386 /* ClearType hinting and grayscale rendering, as used by Universal */
387 /* Windows Platform apps (Windows 8 and above). Like the standard */
388 /* colorful ClearType mode, it utilizes a vastly increased virtual */
389 /* resolution on the x axis. Different from bi-level hinting and */
390 /* grayscale rendering, the old mode from Win9x days that roughly */
391 /* adheres to the physical pixel grid on both axes. */
392 FT_Bool grayscale_cleartype;
393#endif /* TT_SUPPORT_SUBPIXEL_HINTING_MINIMAL */
394
395#ifdef TT_SUPPORT_SUBPIXEL_HINTING_INFINALITY
396 TT_Round_Func func_round_sphn; /* subpixel rounding function */
397
398 FT_Bool subpixel_hinting; /* Using subpixel hinting? */
399 FT_Bool ignore_x_mode; /* Standard rendering mode for */
400 /* subpixel hinting. On if gray */
401 /* or subpixel hinting is on. */
402
403 /* The following 6 aren't fully implemented but here for MS rasterizer */
404 /* compatibility. */
405 FT_Bool compatible_widths; /* compatible widths? */
406 FT_Bool symmetrical_smoothing; /* symmetrical_smoothing? */
407 FT_Bool bgr; /* bgr instead of rgb? */
408 FT_Bool vertical_lcd; /* long side of LCD subpixel */
409 /* rectangles is horizontal */
410 FT_Bool subpixel_positioned; /* subpixel positioned */
411 /* (DirectWrite ClearType)? */
412 FT_Bool gray_cleartype; /* ClearType hinting but */
413 /* grayscale rendering */
414
415 FT_Int rasterizer_version; /* MS rasterizer version */
416
417 FT_Bool iup_called; /* IUP called for glyph? */
418
419 FT_ULong sph_tweak_flags; /* flags to control */
420 /* hint tweaks */
421
422 FT_ULong sph_in_func_flags; /* flags to indicate if in */
423 /* special functions */
424
425#endif /* TT_SUPPORT_SUBPIXEL_HINTING_INFINALITY */
426
427 /* We maintain two counters (in addition to the instruction counter) */
428 /* that act as loop detectors for LOOPCALL and jump opcodes with */
429 /* negative arguments. */
430 FT_ULong loopcall_counter;
431 FT_ULong loopcall_counter_max;
432 FT_ULong neg_jump_counter;
433 FT_ULong neg_jump_counter_max;
434
435 } TT_ExecContextRec;
436
437
438 extern const TT_GraphicsState tt_default_graphics_state;
439
440
441#ifdef TT_USE_BYTECODE_INTERPRETER
442 FT_LOCAL( void )
443 TT_Goto_CodeRange( TT_ExecContext exec,
444 FT_Int range,
445 FT_Long IP );
446
447 FT_LOCAL( void )
448 TT_Set_CodeRange( TT_ExecContext exec,
449 FT_Int range,
450 void* base,
451 FT_Long length );
452
453 FT_LOCAL( void )
454 TT_Clear_CodeRange( TT_ExecContext exec,
455 FT_Int range );
456
457
458 FT_LOCAL( FT_Error )
459 Update_Max( FT_Memory memory,
460 FT_ULong* size,
461 FT_ULong multiplier,
462 void* _pbuff,
463 FT_ULong new_max );
464#endif /* TT_USE_BYTECODE_INTERPRETER */
465
466
467 /**************************************************************************
468 *
469 * @Function:
470 * TT_New_Context
471 *
472 * @Description:
473 * Queries the face context for a given font. Note that there is
474 * now a _single_ execution context in the TrueType driver which is
475 * shared among faces.
476 *
477 * @Input:
478 * face ::
479 * A handle to the source face object.
480 *
481 * @Return:
482 * A handle to the execution context. Initialized for `face'.
483 *
484 * @Note:
485 * Only the glyph loader and debugger should call this function.
486 * (And right now only the glyph loader uses it.)
487 */
488 FT_EXPORT( TT_ExecContext )
489 TT_New_Context( TT_Driver driver );
490
491
492#ifdef TT_USE_BYTECODE_INTERPRETER
493 FT_LOCAL( void )
494 TT_Done_Context( TT_ExecContext exec );
495
496 FT_LOCAL( FT_Error )
497 TT_Load_Context( TT_ExecContext exec,
498 TT_Face face,
499 TT_Size size );
500
501 FT_LOCAL( void )
502 TT_Save_Context( TT_ExecContext exec,
503 TT_Size ins );
504
505 FT_LOCAL( FT_Error )
506 TT_Run_Context( TT_ExecContext exec );
507#endif /* TT_USE_BYTECODE_INTERPRETER */
508
509
510 /**************************************************************************
511 *
512 * @Function:
513 * TT_RunIns
514 *
515 * @Description:
516 * Executes one or more instruction in the execution context. This
517 * is the main function of the TrueType opcode interpreter.
518 *
519 * @Input:
520 * exec ::
521 * A handle to the target execution context.
522 *
523 * @Return:
524 * FreeType error code. 0 means success.
525 *
526 * @Note:
527 * Only the object manager and debugger should call this function.
528 *
529 * This function is publicly exported because it is directly
530 * invoked by the TrueType debugger.
531 */
532 FT_EXPORT( FT_Error )
533 TT_RunIns( TT_ExecContext exec );
534
535
536FT_END_HEADER
537
538#endif /* TTINTERP_H_ */
539
540
541/* END */
542