1 /***************************************************************************/ 2 /* */ 3 /* ftbbox.c */ 4 /* */ 5 /* FreeType bbox computation (body). */ 6 /* */ 7 /* Copyright 1996-2002, 2004, 2006, 2010, 2013 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 /*************************************************************************/ 20 /* */ 21 /* This component has a _single_ role: to compute exact outline bounding */ 22 /* boxes. */ 23 /* */ 24 /*************************************************************************/ 25 26 27 #include <ft2build.h> 28 #include FT_INTERNAL_DEBUG_H 29 30 #include FT_BBOX_H 31 #include FT_IMAGE_H 32 #include FT_OUTLINE_H 33 #include FT_INTERNAL_CALC_H 34 #include FT_INTERNAL_OBJECTS_H 35 36 37 typedef struct TBBox_Rec_ 38 { 39 FT_Vector last; 40 FT_BBox bbox; 41 42 } TBBox_Rec; 43 44 45 /*************************************************************************/ 46 /* */ 47 /* <Function> */ 48 /* BBox_Move_To */ 49 /* */ 50 /* <Description> */ 51 /* This function is used as a `move_to' and `line_to' emitter during */ 52 /* FT_Outline_Decompose(). It simply records the destination point */ 53 /* in `user->last'; no further computations are necessary since we */ 54 /* use the cbox as the starting bbox which must be refined. */ 55 /* */ 56 /* <Input> */ 57 /* to :: A pointer to the destination vector. */ 58 /* */ 59 /* <InOut> */ 60 /* user :: A pointer to the current walk context. */ 61 /* */ 62 /* <Return> */ 63 /* Always 0. Needed for the interface only. */ 64 /* */ 65 static int 66 BBox_Move_To( FT_Vector* to, 67 TBBox_Rec* user ) 68 { 69 user->last = *to; 70 71 return 0; 72 } 73 74 75 #define CHECK_X( p, bbox ) \ 76 ( p->x < bbox.xMin || p->x > bbox.xMax ) 77 78 #define CHECK_Y( p, bbox ) \ 79 ( p->y < bbox.yMin || p->y > bbox.yMax ) 80 81 82 /*************************************************************************/ 83 /* */ 84 /* <Function> */ 85 /* BBox_Conic_Check */ 86 /* */ 87 /* <Description> */ 88 /* Finds the extrema of a 1-dimensional conic Bezier curve and update */ 89 /* a bounding range. This version uses direct computation, as it */ 90 /* doesn't need square roots. */ 91 /* */ 92 /* <Input> */ 93 /* y1 :: The start coordinate. */ 94 /* */ 95 /* y2 :: The coordinate of the control point. */ 96 /* */ 97 /* y3 :: The end coordinate. */ 98 /* */ 99 /* <InOut> */ 100 /* min :: The address of the current minimum. */ 101 /* */ 102 /* max :: The address of the current maximum. */ 103 /* */ 104 static void 105 BBox_Conic_Check( FT_Pos y1, 106 FT_Pos y2, 107 FT_Pos y3, 108 FT_Pos* min, 109 FT_Pos* max ) 110 { 111 if ( y1 <= y3 && y2 == y1 ) /* flat arc */ 112 goto Suite; 113 114 if ( y1 < y3 ) 115 { 116 if ( y2 >= y1 && y2 <= y3 ) /* ascending arc */ 117 goto Suite; 118 } 119 else 120 { 121 if ( y2 >= y3 && y2 <= y1 ) /* descending arc */ 122 { 123 y2 = y1; 124 y1 = y3; 125 y3 = y2; 126 goto Suite; 127 } 128 } 129 130 y1 = y3 = y1 - FT_MulDiv( y2 - y1, y2 - y1, y1 - 2*y2 + y3 ); 131 132 Suite: 133 if ( y1 < *min ) *min = y1; 134 if ( y3 > *max ) *max = y3; 135 } 136 137 138 /*************************************************************************/ 139 /* */ 140 /* <Function> */ 141 /* BBox_Conic_To */ 142 /* */ 143 /* <Description> */ 144 /* This function is used as a `conic_to' emitter during */ 145 /* FT_Outline_Decompose(). It checks a conic Bezier curve with the */ 146 /* current bounding box, and computes its extrema if necessary to */ 147 /* update it. */ 148 /* */ 149 /* <Input> */ 150 /* control :: A pointer to a control point. */ 151 /* */ 152 /* to :: A pointer to the destination vector. */ 153 /* */ 154 /* <InOut> */ 155 /* user :: The address of the current walk context. */ 156 /* */ 157 /* <Return> */ 158 /* Always 0. Needed for the interface only. */ 159 /* */ 160 /* <Note> */ 161 /* In the case of a non-monotonous arc, we compute directly the */ 162 /* extremum coordinates, as it is sufficiently fast. */ 163 /* */ 164 static int 165 BBox_Conic_To( FT_Vector* control, 166 FT_Vector* to, 167 TBBox_Rec* user ) 168 { 169 /* we don't need to check `to' since it is always an `on' point, thus */ 170 /* within the bbox */ 171 172 if ( CHECK_X( control, user->bbox ) ) 173 BBox_Conic_Check( user->last.x, 174 control->x, 175 to->x, 176 &user->bbox.xMin, 177 &user->bbox.xMax ); 178 179 if ( CHECK_Y( control, user->bbox ) ) 180 BBox_Conic_Check( user->last.y, 181 control->y, 182 to->y, 183 &user->bbox.yMin, 184 &user->bbox.yMax ); 185 186 user->last = *to; 187 188 return 0; 189 } 190 191 192 /*************************************************************************/ 193 /* */ 194 /* <Function> */ 195 /* BBox_Cubic_Check */ 196 /* */ 197 /* <Description> */ 198 /* Finds the extrema of a 1-dimensional cubic Bezier curve and */ 199 /* updates a bounding range. This version uses splitting because we */ 200 /* don't want to use square roots and extra accuracy. */ 201 /* */ 202 /* <Input> */ 203 /* p1 :: The start coordinate. */ 204 /* */ 205 /* p2 :: The coordinate of the first control point. */ 206 /* */ 207 /* p3 :: The coordinate of the second control point. */ 208 /* */ 209 /* p4 :: The end coordinate. */ 210 /* */ 211 /* <InOut> */ 212 /* min :: The address of the current minimum. */ 213 /* */ 214 /* max :: The address of the current maximum. */ 215 /* */ 216 217 #if 0 218 219 static void 220 BBox_Cubic_Check( FT_Pos p1, 221 FT_Pos p2, 222 FT_Pos p3, 223 FT_Pos p4, 224 FT_Pos* min, 225 FT_Pos* max ) 226 { 227 FT_Pos q1, q2, q3, q4; 228 229 230 q1 = p1; 231 q2 = p2; 232 q3 = p3; 233 q4 = p4; 234 235 /* for a conic segment to possibly reach new maximum */ 236 /* one of its off-points must be above the current value */ 237 while ( q2 > *max || q3 > *max ) 238 { 239 /* determine which half contains the maximum and split */ 240 if ( q1 + q2 > q3 + q4 ) /* first half */ 241 { 242 q4 = q4 + q3; 243 q3 = q3 + q2; 244 q2 = q2 + q1; 245 q4 = q4 + q3; 246 q3 = q3 + q2; 247 q4 = ( q4 + q3 ) / 8; 248 q3 = q3 / 4; 249 q2 = q2 / 2; 250 } 251 else /* second half */ 252 { 253 q1 = q1 + q2; 254 q2 = q2 + q3; 255 q3 = q3 + q4; 256 q1 = q1 + q2; 257 q2 = q2 + q3; 258 q1 = ( q1 + q2 ) / 8; 259 q2 = q2 / 4; 260 q3 = q3 / 2; 261 } 262 263 /* check if either end reached the maximum */ 264 if ( q1 == q2 && q1 >= q3 ) 265 { 266 *max = q1; 267 break; 268 } 269 if ( q3 == q4 && q2 <= q4 ) 270 { 271 *max = q4; 272 break; 273 } 274 } 275 276 q1 = p1; 277 q2 = p2; 278 q3 = p3; 279 q4 = p4; 280 281 /* for a conic segment to possibly reach new minimum */ 282 /* one of its off-points must be below the current value */ 283 while ( q2 < *min || q3 < *min ) 284 { 285 /* determine which half contains the minimum and split */ 286 if ( q1 + q2 < q3 + q4 ) /* first half */ 287 { 288 q4 = q4 + q3; 289 q3 = q3 + q2; 290 q2 = q2 + q1; 291 q4 = q4 + q3; 292 q3 = q3 + q2; 293 q4 = ( q4 + q3 ) / 8; 294 q3 = q3 / 4; 295 q2 = q2 / 2; 296 } 297 else /* second half */ 298 { 299 q1 = q1 + q2; 300 q2 = q2 + q3; 301 q3 = q3 + q4; 302 q1 = q1 + q2; 303 q2 = q2 + q3; 304 q1 = ( q1 + q2 ) / 8; 305 q2 = q2 / 4; 306 q3 = q3 / 2; 307 } 308 309 /* check if either end reached the minimum */ 310 if ( q1 == q2 && q1 <= q3 ) 311 { 312 *min = q1; 313 break; 314 } 315 if ( q3 == q4 && q2 >= q4 ) 316 { 317 *min = q4; 318 break; 319 } 320 } 321 } 322 323 #else 324 325 static void 326 test_cubic_extrema( FT_Pos y1, 327 FT_Pos y2, 328 FT_Pos y3, 329 FT_Pos y4, 330 FT_Fixed u, 331 FT_Pos* min, 332 FT_Pos* max ) 333 { 334 /* FT_Pos a = y4 - 3*y3 + 3*y2 - y1; */ 335 FT_Pos b = y3 - 2*y2 + y1; 336 FT_Pos c = y2 - y1; 337 FT_Pos d = y1; 338 FT_Pos y; 339 FT_Fixed uu; 340 341 FT_UNUSED ( y4 ); 342 343 344 /* The polynomial is */ 345 /* */ 346 /* P(x) = a*x^3 + 3b*x^2 + 3c*x + d , */ 347 /* */ 348 /* dP/dx = 3a*x^2 + 6b*x + 3c . */ 349 /* */ 350 /* However, we also have */ 351 /* */ 352 /* dP/dx(u) = 0 , */ 353 /* */ 354 /* which implies by subtraction that */ 355 /* */ 356 /* P(u) = b*u^2 + 2c*u + d . */ 357 358 if ( u > 0 && u < 0x10000L ) 359 { 360 uu = FT_MulFix( u, u ); 361 y = d + FT_MulFix( c, 2*u ) + FT_MulFix( b, uu ); 362 363 if ( y < *min ) *min = y; 364 if ( y > *max ) *max = y; 365 } 366 } 367 368 369 static void 370 BBox_Cubic_Check( FT_Pos y1, 371 FT_Pos y2, 372 FT_Pos y3, 373 FT_Pos y4, 374 FT_Pos* min, 375 FT_Pos* max ) 376 { 377 /* always compare first and last points */ 378 if ( y1 < *min ) *min = y1; 379 else if ( y1 > *max ) *max = y1; 380 381 if ( y4 < *min ) *min = y4; 382 else if ( y4 > *max ) *max = y4; 383 384 /* now, try to see if there are split points here */ 385 if ( y1 <= y4 ) 386 { 387 /* flat or ascending arc test */ 388 if ( y1 <= y2 && y2 <= y4 && y1 <= y3 && y3 <= y4 ) 389 return; 390 } 391 else /* y1 > y4 */ 392 { 393 /* descending arc test */ 394 if ( y1 >= y2 && y2 >= y4 && y1 >= y3 && y3 >= y4 ) 395 return; 396 } 397 398 /* There are some split points. Find them. */ 399 /* We already made sure that a, b, and c below cannot be all zero. */ 400 { 401 FT_Pos a = y4 - 3*y3 + 3*y2 - y1; 402 FT_Pos b = y3 - 2*y2 + y1; 403 FT_Pos c = y2 - y1; 404 FT_Pos d; 405 FT_Fixed t; 406 FT_Int shift; 407 408 409 /* We need to solve `ax^2+2bx+c' here, without floating points! */ 410 /* The trick is to normalize to a different representation in order */ 411 /* to use our 16.16 fixed-point routines. */ 412 /* */ 413 /* We compute FT_MulFix(b,b) and FT_MulFix(a,c) after normalization. */ 414 /* These values must fit into a single 16.16 value. */ 415 /* */ 416 /* We normalize a, b, and c to `8.16' fixed-point values to ensure */ 417 /* that their product is held in a `16.16' value including the sign. */ 418 /* Necessarily, we need to shift `a', `b', and `c' so that the most */ 419 /* significant bit of their absolute values is at position 22. */ 420 /* */ 421 /* This also means that we are using 23 bits of precision to compute */ 422 /* the zeros, independently of the range of the original polynomial */ 423 /* coefficients. */ 424 /* */ 425 /* This algorithm should ensure reasonably accurate values for the */ 426 /* zeros. Note that they are only expressed with 16 bits when */ 427 /* computing the extrema (the zeros need to be in 0..1 exclusive */ 428 /* to be considered part of the arc). */ 429 430 shift = FT_MSB( FT_ABS( a ) | FT_ABS( b ) | FT_ABS( c ) ); 431 432 if ( shift > 22 ) 433 { 434 shift -= 22; 435 436 /* this loses some bits of precision, but we use 23 of them */ 437 /* for the computation anyway */ 438 a >>= shift; 439 b >>= shift; 440 c >>= shift; 441 } 442 else 443 { 444 shift = 22 - shift; 445 446 a <<= shift; 447 b <<= shift; 448 c <<= shift; 449 } 450 451 /* handle a == 0 */ 452 if ( a == 0 ) 453 { 454 if ( b != 0 ) 455 { 456 t = - FT_DivFix( c, b ) / 2; 457 test_cubic_extrema( y1, y2, y3, y4, t, min, max ); 458 } 459 } 460 else 461 { 462 /* solve the equation now */ 463 d = FT_MulFix( b, b ) - FT_MulFix( a, c ); 464 if ( d < 0 ) 465 return; 466 467 if ( d == 0 ) 468 { 469 /* there is a single split point at -b/a */ 470 t = - FT_DivFix( b, a ); 471 test_cubic_extrema( y1, y2, y3, y4, t, min, max ); 472 } 473 else 474 { 475 /* there are two solutions; we need to filter them */ 476 d = FT_SqrtFixed( (FT_Int32)d ); 477 t = - FT_DivFix( b - d, a ); 478 test_cubic_extrema( y1, y2, y3, y4, t, min, max ); 479 480 t = - FT_DivFix( b + d, a ); 481 test_cubic_extrema( y1, y2, y3, y4, t, min, max ); 482 } 483 } 484 } 485 } 486 487 #endif 488 489 490 /*************************************************************************/ 491 /* */ 492 /* <Function> */ 493 /* BBox_Cubic_To */ 494 /* */ 495 /* <Description> */ 496 /* This function is used as a `cubic_to' emitter during */ 497 /* FT_Outline_Decompose(). It checks a cubic Bezier curve with the */ 498 /* current bounding box, and computes its extrema if necessary to */ 499 /* update it. */ 500 /* */ 501 /* <Input> */ 502 /* control1 :: A pointer to the first control point. */ 503 /* */ 504 /* control2 :: A pointer to the second control point. */ 505 /* */ 506 /* to :: A pointer to the destination vector. */ 507 /* */ 508 /* <InOut> */ 509 /* user :: The address of the current walk context. */ 510 /* */ 511 /* <Return> */ 512 /* Always 0. Needed for the interface only. */ 513 /* */ 514 /* <Note> */ 515 /* In the case of a non-monotonous arc, we don't compute directly */ 516 /* extremum coordinates, we subdivide instead. */ 517 /* */ 518 static int 519 BBox_Cubic_To( FT_Vector* control1, 520 FT_Vector* control2, 521 FT_Vector* to, 522 TBBox_Rec* user ) 523 { 524 /* we don't need to check `to' since it is always an `on' point, thus */ 525 /* within the bbox */ 526 527 if ( CHECK_X( control1, user->bbox ) || 528 CHECK_X( control2, user->bbox ) ) 529 BBox_Cubic_Check( user->last.x, 530 control1->x, 531 control2->x, 532 to->x, 533 &user->bbox.xMin, 534 &user->bbox.xMax ); 535 536 if ( CHECK_Y( control1, user->bbox ) || 537 CHECK_Y( control2, user->bbox ) ) 538 BBox_Cubic_Check( user->last.y, 539 control1->y, 540 control2->y, 541 to->y, 542 &user->bbox.yMin, 543 &user->bbox.yMax ); 544 545 user->last = *to; 546 547 return 0; 548 } 549 550 FT_DEFINE_OUTLINE_FUNCS(bbox_interface, 551 (FT_Outline_MoveTo_Func) BBox_Move_To, 552 (FT_Outline_LineTo_Func) BBox_Move_To, 553 (FT_Outline_ConicTo_Func)BBox_Conic_To, 554 (FT_Outline_CubicTo_Func)BBox_Cubic_To, 555 0, 0 556 ) 557 558 /* documentation is in ftbbox.h */ 559 560 FT_EXPORT_DEF( FT_Error ) 561 FT_Outline_Get_BBox( FT_Outline* outline, 562 FT_BBox *abbox ) 563 { 564 FT_BBox cbox; 565 FT_BBox bbox; 566 FT_Vector* vec; 567 FT_UShort n; 568 569 570 if ( !abbox ) 571 return FT_THROW( Invalid_Argument ); 572 573 if ( !outline ) 574 return FT_THROW( Invalid_Outline ); 575 576 /* if outline is empty, return (0,0,0,0) */ 577 if ( outline->n_points == 0 || outline->n_contours <= 0 ) 578 { 579 abbox->xMin = abbox->xMax = 0; 580 abbox->yMin = abbox->yMax = 0; 581 return 0; 582 } 583 584 /* We compute the control box as well as the bounding box of */ 585 /* all `on' points in the outline. Then, if the two boxes */ 586 /* coincide, we exit immediately. */ 587 588 vec = outline->points; 589 bbox.xMin = bbox.xMax = cbox.xMin = cbox.xMax = vec->x; 590 bbox.yMin = bbox.yMax = cbox.yMin = cbox.yMax = vec->y; 591 vec++; 592 593 for ( n = 1; n < outline->n_points; n++ ) 594 { 595 FT_Pos x = vec->x; 596 FT_Pos y = vec->y; 597 598 599 /* update control box */ 600 if ( x < cbox.xMin ) cbox.xMin = x; 601 if ( x > cbox.xMax ) cbox.xMax = x; 602 603 if ( y < cbox.yMin ) cbox.yMin = y; 604 if ( y > cbox.yMax ) cbox.yMax = y; 605 606 if ( FT_CURVE_TAG( outline->tags[n] ) == FT_CURVE_TAG_ON ) 607 { 608 /* update bbox for `on' points only */ 609 if ( x < bbox.xMin ) bbox.xMin = x; 610 if ( x > bbox.xMax ) bbox.xMax = x; 611 612 if ( y < bbox.yMin ) bbox.yMin = y; 613 if ( y > bbox.yMax ) bbox.yMax = y; 614 } 615 616 vec++; 617 } 618 619 /* test two boxes for equality */ 620 if ( cbox.xMin < bbox.xMin || cbox.xMax > bbox.xMax || 621 cbox.yMin < bbox.yMin || cbox.yMax > bbox.yMax ) 622 { 623 /* the two boxes are different, now walk over the outline to */ 624 /* get the Bezier arc extrema. */ 625 626 FT_Error error; 627 TBBox_Rec user; 628 629 #ifdef FT_CONFIG_OPTION_PIC 630 FT_Outline_Funcs bbox_interface; 631 Init_Class_bbox_interface(&bbox_interface); 632 #endif 633 634 user.bbox = bbox; 635 636 error = FT_Outline_Decompose( outline, &bbox_interface, &user ); 637 if ( error ) 638 return error; 639 640 *abbox = user.bbox; 641 } 642 else 643 *abbox = bbox; 644 645 return FT_Err_Ok; 646 } 647 648 649 /* END */ 650
