SkDashPathEffect.cpp revision 4bbdeac58cc928dc66296bde3bd06e78070d96b7
1 2/* 3 * Copyright 2006 The Android Open Source Project 4 * 5 * Use of this source code is governed by a BSD-style license that can be 6 * found in the LICENSE file. 7 */ 8 9 10#include "SkDashPathEffect.h" 11#include "SkFlattenableBuffers.h" 12#include "SkPathMeasure.h" 13 14static inline int is_even(int x) { 15 return (~x) << 31; 16} 17 18static SkScalar FindFirstInterval(const SkScalar intervals[], SkScalar phase, 19 int32_t* index, int count) { 20 for (int i = 0; i < count; ++i) { 21 if (phase > intervals[i]) { 22 phase -= intervals[i]; 23 } else { 24 *index = i; 25 return intervals[i] - phase; 26 } 27 } 28 // If we get here, phase "appears" to be larger than our length. This 29 // shouldn't happen with perfect precision, but we can accumulate errors 30 // during the initial length computation (rounding can make our sum be too 31 // big or too small. In that event, we just have to eat the error here. 32 *index = 0; 33 return intervals[0]; 34} 35 36SkDashPathEffect::SkDashPathEffect(const SkScalar intervals[], int count, 37 SkScalar phase, bool scaleToFit) 38 : fScaleToFit(scaleToFit) { 39 SkASSERT(intervals); 40 SkASSERT(count > 1 && SkAlign2(count) == count); 41 42 fIntervals = (SkScalar*)sk_malloc_throw(sizeof(SkScalar) * count); 43 fCount = count; 44 45 SkScalar len = 0; 46 for (int i = 0; i < count; i++) { 47 SkASSERT(intervals[i] >= 0); 48 fIntervals[i] = intervals[i]; 49 len += intervals[i]; 50 } 51 fIntervalLength = len; 52 53 // watch out for values that might make us go out of bounds 54 if ((len > 0) && SkScalarIsFinite(phase) && SkScalarIsFinite(len)) { 55 56 // Adjust phase to be between 0 and len, "flipping" phase if negative. 57 // e.g., if len is 100, then phase of -20 (or -120) is equivalent to 80 58 if (phase < 0) { 59 phase = -phase; 60 if (phase > len) { 61 phase = SkScalarMod(phase, len); 62 } 63 phase = len - phase; 64 65 // Due to finite precision, it's possible that phase == len, 66 // even after the subtract (if len >>> phase), so fix that here. 67 // This fixes http://crbug.com/124652 . 68 SkASSERT(phase <= len); 69 if (phase == len) { 70 phase = 0; 71 } 72 } else if (phase >= len) { 73 phase = SkScalarMod(phase, len); 74 } 75 SkASSERT(phase >= 0 && phase < len); 76 77 fInitialDashLength = FindFirstInterval(intervals, phase, 78 &fInitialDashIndex, count); 79 80 SkASSERT(fInitialDashLength >= 0); 81 SkASSERT(fInitialDashIndex >= 0 && fInitialDashIndex < fCount); 82 } else { 83 fInitialDashLength = -1; // signal bad dash intervals 84 } 85} 86 87SkDashPathEffect::~SkDashPathEffect() { 88 sk_free(fIntervals); 89} 90 91static void outset_for_stroke(SkRect* rect, const SkStrokeRec& rec) { 92 SkScalar radius = SkScalarHalf(rec.getWidth()); 93 if (0 == radius) { 94 radius = SK_Scalar1; // hairlines 95 } 96 if (SkPaint::kMiter_Join == rec.getJoin()) { 97 radius = SkScalarMul(radius, rec.getMiter()); 98 } 99 rect->outset(radius, radius); 100} 101 102// Only handles lines for now. If returns true, dstPath is the new (smaller) 103// path. If returns false, then dstPath parameter is ignored. 104static bool cull_path(const SkPath& srcPath, const SkStrokeRec& rec, 105 const SkRect* cullRect, SkScalar intervalLength, 106 SkPath* dstPath) { 107 if (NULL == cullRect) { 108 return false; 109 } 110 111 SkPoint pts[2]; 112 if (!srcPath.isLine(pts)) { 113 return false; 114 } 115 116 SkRect bounds = *cullRect; 117 outset_for_stroke(&bounds, rec); 118 119 SkScalar dx = pts[1].x() - pts[0].x(); 120 SkScalar dy = pts[1].y() - pts[0].y(); 121 122 // just do horizontal lines for now (lazy) 123 if (dy) { 124 return false; 125 } 126 127 SkScalar minX = pts[0].fX; 128 SkScalar maxX = pts[1].fX; 129 130 if (maxX < bounds.fLeft || minX > bounds.fRight) { 131 return false; 132 } 133 134 if (dx < 0) { 135 SkTSwap(minX, maxX); 136 } 137 138 // Now we actually perform the chop, removing the excess to the left and 139 // right of the bounds (keeping our new line "in phase" with the dash, 140 // hence the (mod intervalLength). 141 142 if (minX < bounds.fLeft) { 143 minX = bounds.fLeft - SkScalarMod(bounds.fLeft - minX, 144 intervalLength); 145 } 146 if (maxX > bounds.fRight) { 147 maxX = bounds.fRight + SkScalarMod(maxX - bounds.fRight, 148 intervalLength); 149 } 150 151 SkASSERT(maxX > minX); 152 if (dx < 0) { 153 SkTSwap(minX, maxX); 154 } 155 pts[0].fX = minX; 156 pts[1].fX = maxX; 157 158 dstPath->moveTo(pts[0]); 159 dstPath->lineTo(pts[1]); 160 return true; 161} 162 163class SpecialLineRec { 164public: 165 bool init(const SkPath& src, SkPath* dst, SkStrokeRec* rec, 166 int intervalCount, SkScalar intervalLength) { 167 if (rec->isHairlineStyle() || !src.isLine(fPts)) { 168 return false; 169 } 170 171 // can relax this in the future, if we handle square and round caps 172 if (SkPaint::kButt_Cap != rec->getCap()) { 173 return false; 174 } 175 176 SkScalar pathLength = SkPoint::Distance(fPts[0], fPts[1]); 177 178 fTangent = fPts[1] - fPts[0]; 179 if (fTangent.isZero()) { 180 return false; 181 } 182 183 fPathLength = pathLength; 184 fTangent.scale(SkScalarInvert(pathLength)); 185 fTangent.rotateCCW(&fNormal); 186 fNormal.scale(SkScalarHalf(rec->getWidth())); 187 188 // now estimate how many quads will be added to the path 189 // resulting segments = pathLen * intervalCount / intervalLen 190 // resulting points = 4 * segments 191 192 SkScalar ptCount = SkScalarMulDiv(pathLength, 193 SkIntToScalar(intervalCount), 194 intervalLength); 195 int n = SkScalarCeilToInt(ptCount) << 2; 196 dst->incReserve(n); 197 198 // we will take care of the stroking 199 rec->setFillStyle(); 200 return true; 201 } 202 203 void addSegment(SkScalar d0, SkScalar d1, SkPath* path) const { 204 SkASSERT(d0 < fPathLength); 205 // clamp the segment to our length 206 if (d1 > fPathLength) { 207 d1 = fPathLength; 208 } 209 210 SkScalar x0 = fPts[0].fX + SkScalarMul(fTangent.fX, d0); 211 SkScalar x1 = fPts[0].fX + SkScalarMul(fTangent.fX, d1); 212 SkScalar y0 = fPts[0].fY + SkScalarMul(fTangent.fY, d0); 213 SkScalar y1 = fPts[0].fY + SkScalarMul(fTangent.fY, d1); 214 215 SkPoint pts[4]; 216 pts[0].set(x0 + fNormal.fX, y0 + fNormal.fY); // moveTo 217 pts[1].set(x1 + fNormal.fX, y1 + fNormal.fY); // lineTo 218 pts[2].set(x1 - fNormal.fX, y1 - fNormal.fY); // lineTo 219 pts[3].set(x0 - fNormal.fX, y0 - fNormal.fY); // lineTo 220 221 path->addPoly(pts, SK_ARRAY_COUNT(pts), false); 222 } 223 224private: 225 SkPoint fPts[2]; 226 SkVector fTangent; 227 SkVector fNormal; 228 SkScalar fPathLength; 229}; 230 231bool SkDashPathEffect::filterPath(SkPath* dst, const SkPath& src, 232 SkStrokeRec* rec, const SkRect* cullRect) const { 233 // we do nothing if the src wants to be filled, or if our dashlength is 0 234 if (rec->isFillStyle() || fInitialDashLength < 0) { 235 return false; 236 } 237 238 const SkScalar* intervals = fIntervals; 239 SkScalar dashCount = 0; 240 241 SkPath cullPathStorage; 242 const SkPath* srcPtr = &src; 243 if (cull_path(src, *rec, cullRect, fIntervalLength, &cullPathStorage)) { 244 srcPtr = &cullPathStorage; 245 } 246 247 SpecialLineRec lineRec; 248 bool specialLine = lineRec.init(src, dst, rec, fCount >> 1, fIntervalLength); 249 250 SkPathMeasure meas(*srcPtr, false); 251 252 do { 253 bool skipFirstSegment = meas.isClosed(); 254 bool addedSegment = false; 255 SkScalar length = meas.getLength(); 256 int index = fInitialDashIndex; 257 SkScalar scale = SK_Scalar1; 258 259 // Since the path length / dash length ratio may be arbitrarily large, we can exert 260 // significant memory pressure while attempting to build the filtered path. To avoid this, 261 // we simply give up dashing beyond a certain threshold. 262 // 263 // The original bug report (http://crbug.com/165432) is based on a path yielding more than 264 // 90 million dash segments and crashing the memory allocator. A limit of 1 million 265 // segments seems reasonable: at 2 verbs per segment * 9 bytes per verb, this caps the 266 // maximum dash memory overhead at roughly 17MB per path. 267 static const SkScalar kMaxDashCount = 1000000; 268 dashCount += length * (fCount >> 1) / fIntervalLength; 269 if (dashCount > kMaxDashCount) { 270 dst->reset(); 271 return false; 272 } 273 274 if (fScaleToFit) { 275 if (fIntervalLength >= length) { 276 scale = SkScalarDiv(length, fIntervalLength); 277 } else { 278 SkScalar div = SkScalarDiv(length, fIntervalLength); 279 int n = SkScalarFloor(div); 280 scale = SkScalarDiv(length, n * fIntervalLength); 281 } 282 } 283 284 // Using double precision to avoid looping indefinitely due to single precision rounding 285 // (for extreme path_length/dash_length ratios). See test_infinite_dash() unittest. 286 double distance = 0; 287 double dlen = SkScalarMul(fInitialDashLength, scale); 288 289 while (distance < length) { 290 SkASSERT(dlen >= 0); 291 addedSegment = false; 292 if (is_even(index) && dlen > 0 && !skipFirstSegment) { 293 addedSegment = true; 294 295 if (specialLine) { 296 lineRec.addSegment(SkDoubleToScalar(distance), 297 SkDoubleToScalar(distance + dlen), 298 dst); 299 } else { 300 meas.getSegment(SkDoubleToScalar(distance), 301 SkDoubleToScalar(distance + dlen), 302 dst, true); 303 } 304 } 305 distance += dlen; 306 307 // clear this so we only respect it the first time around 308 skipFirstSegment = false; 309 310 // wrap around our intervals array if necessary 311 index += 1; 312 SkASSERT(index <= fCount); 313 if (index == fCount) { 314 index = 0; 315 } 316 317 // fetch our next dlen 318 dlen = SkScalarMul(intervals[index], scale); 319 } 320 321 // extend if we ended on a segment and we need to join up with the (skipped) initial segment 322 if (meas.isClosed() && is_even(fInitialDashIndex) && 323 fInitialDashLength > 0) { 324 meas.getSegment(0, SkScalarMul(fInitialDashLength, scale), dst, !addedSegment); 325 } 326 } while (meas.nextContour()); 327 328 return true; 329} 330 331// Currently asPoints is more restrictive then it needs to be. In the future 332// we need to: 333// allow kRound_Cap capping (could allow rotations in the matrix with this) 334// allow paths to be returned 335bool SkDashPathEffect::asPoints(PointData* results, 336 const SkPath& src, 337 const SkStrokeRec& rec, 338 const SkMatrix& matrix, 339 const SkRect* cullRect) const { 340 // width < 0 -> fill && width == 0 -> hairline so requiring width > 0 rules both out 341 if (fInitialDashLength < 0 || 0 >= rec.getWidth()) { 342 return false; 343 } 344 345 // TODO: this next test could be eased up. We could allow any number of 346 // intervals as long as all the ons match and all the offs match. 347 // Additionally, they do not necessarily need to be integers. 348 // We cannot allow arbitrary intervals since we want the returned points 349 // to be uniformly sized. 350 if (fCount != 2 || 351 !SkScalarNearlyEqual(fIntervals[0], fIntervals[1]) || 352 !SkScalarIsInt(fIntervals[0]) || 353 !SkScalarIsInt(fIntervals[1])) { 354 return false; 355 } 356 357 // TODO: this next test could be eased up. The rescaling should not impact 358 // the equality of the ons & offs. However, we would need to remove the 359 // integer intervals restriction first 360 if (fScaleToFit) { 361 return false; 362 } 363 364 SkPoint pts[2]; 365 366 if (!src.isLine(pts)) { 367 return false; 368 } 369 370 // TODO: this test could be eased up to allow circles 371 if (SkPaint::kButt_Cap != rec.getCap()) { 372 return false; 373 } 374 375 // TODO: this test could be eased up for circles. Rotations could be allowed. 376 if (!matrix.rectStaysRect()) { 377 return false; 378 } 379 380 SkScalar length = SkPoint::Distance(pts[1], pts[0]); 381 382 SkVector tangent = pts[1] - pts[0]; 383 if (tangent.isZero()) { 384 return false; 385 } 386 387 tangent.scale(SkScalarInvert(length)); 388 389 // TODO: make this test for horizontal & vertical lines more robust 390 bool isXAxis = true; 391 if (SK_Scalar1 == tangent.fX || -SK_Scalar1 == tangent.fX) { 392 results->fSize.set(SkScalarHalf(fIntervals[0]), SkScalarHalf(rec.getWidth())); 393 } else if (SK_Scalar1 == tangent.fY || -SK_Scalar1 == tangent.fY) { 394 results->fSize.set(SkScalarHalf(rec.getWidth()), SkScalarHalf(fIntervals[0])); 395 isXAxis = false; 396 } else if (SkPaint::kRound_Cap != rec.getCap()) { 397 // Angled lines don't have axis-aligned boxes. 398 return false; 399 } 400 401 if (NULL != results) { 402 results->fFlags = 0; 403 SkScalar clampedInitialDashLength = SkMinScalar(length, fInitialDashLength); 404 405 if (SkPaint::kRound_Cap == rec.getCap()) { 406 results->fFlags |= PointData::kCircles_PointFlag; 407 } 408 409 results->fNumPoints = 0; 410 SkScalar len2 = length; 411 bool partialFirst = false; 412 if (clampedInitialDashLength > 0 || 0 == fInitialDashIndex) { 413 SkASSERT(len2 >= clampedInitialDashLength); 414 if (0 == fInitialDashIndex) { 415 if (clampedInitialDashLength > 0) { 416 partialFirst = true; 417 if (clampedInitialDashLength >= fIntervals[0]) { 418 ++results->fNumPoints; // partial first dash 419 } 420 len2 -= clampedInitialDashLength; 421 } 422 len2 -= fIntervals[1]; // also skip first space 423 if (len2 < 0) { 424 len2 = 0; 425 } 426 } else { 427 len2 -= clampedInitialDashLength; // skip initial partial empty 428 } 429 } 430 int numMidPoints = SkScalarFloorToInt(SkScalarDiv(len2, fIntervalLength)); 431 results->fNumPoints += numMidPoints; 432 len2 -= numMidPoints * fIntervalLength; 433 bool partialLast = false; 434 if (len2 > 0) { 435 if (len2 < fIntervals[0]) { 436 partialLast = true; 437 } else { 438 ++numMidPoints; 439 ++results->fNumPoints; 440 } 441 } 442 443 results->fPoints = new SkPoint[results->fNumPoints]; 444 445 SkScalar distance = 0; 446 int curPt = 0; 447 448 if (clampedInitialDashLength > 0 || 0 == fInitialDashIndex) { 449 SkASSERT(clampedInitialDashLength <= length); 450 451 if (0 == fInitialDashIndex) { 452 if (clampedInitialDashLength > 0) { 453 // partial first block 454 SkASSERT(SkPaint::kRound_Cap != rec.getCap()); // can't handle partial circles 455 SkScalar x = pts[0].fX + SkScalarMul(tangent.fX, SkScalarHalf(clampedInitialDashLength)); 456 SkScalar y = pts[0].fY + SkScalarMul(tangent.fY, SkScalarHalf(clampedInitialDashLength)); 457 SkScalar halfWidth, halfHeight; 458 if (isXAxis) { 459 halfWidth = SkScalarHalf(clampedInitialDashLength); 460 halfHeight = SkScalarHalf(rec.getWidth()); 461 } else { 462 halfWidth = SkScalarHalf(rec.getWidth()); 463 halfHeight = SkScalarHalf(clampedInitialDashLength); 464 } 465 if (clampedInitialDashLength < fIntervals[0]) { 466 // This one will not be like the others 467 results->fFirst.addRect(x - halfWidth, y - halfHeight, 468 x + halfWidth, y + halfHeight); 469 } else { 470 SkASSERT(curPt < results->fNumPoints); 471 results->fPoints[curPt].set(x, y); 472 ++curPt; 473 } 474 475 distance += clampedInitialDashLength; 476 } 477 478 distance += fIntervals[1]; // skip over the next blank block too 479 } else { 480 distance += clampedInitialDashLength; 481 } 482 } 483 484 if (0 != numMidPoints) { 485 distance += SkScalarHalf(fIntervals[0]); 486 487 for (int i = 0; i < numMidPoints; ++i) { 488 SkScalar x = pts[0].fX + SkScalarMul(tangent.fX, distance); 489 SkScalar y = pts[0].fY + SkScalarMul(tangent.fY, distance); 490 491 SkASSERT(curPt < results->fNumPoints); 492 results->fPoints[curPt].set(x, y); 493 ++curPt; 494 495 distance += fIntervalLength; 496 } 497 498 distance -= SkScalarHalf(fIntervals[0]); 499 } 500 501 if (partialLast) { 502 // partial final block 503 SkASSERT(SkPaint::kRound_Cap != rec.getCap()); // can't handle partial circles 504 SkScalar temp = length - distance; 505 SkASSERT(temp < fIntervals[0]); 506 SkScalar x = pts[0].fX + SkScalarMul(tangent.fX, distance + SkScalarHalf(temp)); 507 SkScalar y = pts[0].fY + SkScalarMul(tangent.fY, distance + SkScalarHalf(temp)); 508 SkScalar halfWidth, halfHeight; 509 if (isXAxis) { 510 halfWidth = SkScalarHalf(temp); 511 halfHeight = SkScalarHalf(rec.getWidth()); 512 } else { 513 halfWidth = SkScalarHalf(rec.getWidth()); 514 halfHeight = SkScalarHalf(temp); 515 } 516 results->fLast.addRect(x - halfWidth, y - halfHeight, 517 x + halfWidth, y + halfHeight); 518 } 519 520 SkASSERT(curPt == results->fNumPoints); 521 } 522 523 return true; 524} 525 526SkFlattenable::Factory SkDashPathEffect::getFactory() { 527 return fInitialDashLength < 0 ? NULL : CreateProc; 528} 529 530void SkDashPathEffect::flatten(SkFlattenableWriteBuffer& buffer) const { 531 SkASSERT(fInitialDashLength >= 0); 532 533 this->INHERITED::flatten(buffer); 534 buffer.writeInt(fInitialDashIndex); 535 buffer.writeScalar(fInitialDashLength); 536 buffer.writeScalar(fIntervalLength); 537 buffer.writeBool(fScaleToFit); 538 buffer.writeScalarArray(fIntervals, fCount); 539} 540 541SkFlattenable* SkDashPathEffect::CreateProc(SkFlattenableReadBuffer& buffer) { 542 return SkNEW_ARGS(SkDashPathEffect, (buffer)); 543} 544 545SkDashPathEffect::SkDashPathEffect(SkFlattenableReadBuffer& buffer) : INHERITED(buffer) { 546 fInitialDashIndex = buffer.readInt(); 547 fInitialDashLength = buffer.readScalar(); 548 fIntervalLength = buffer.readScalar(); 549 fScaleToFit = buffer.readBool(); 550 551 fCount = buffer.getArrayCount(); 552 fIntervals = (SkScalar*)sk_malloc_throw(sizeof(SkScalar) * fCount); 553 buffer.readScalarArray(fIntervals); 554} 555