1/* 2 * Copyright 2014 Google Inc. 3 * 4 * Use of this source code is governed by a BSD-style license that can be 5 * found in the LICENSE file. 6 */ 7 8#include "SkDashPathPriv.h" 9#include "SkPathMeasure.h" 10 11static inline int is_even(int x) { 12 return (~x) << 31; 13} 14 15static SkScalar find_first_interval(const SkScalar intervals[], SkScalar phase, 16 int32_t* index, int count) { 17 for (int i = 0; i < count; ++i) { 18 if (phase > intervals[i]) { 19 phase -= intervals[i]; 20 } else { 21 *index = i; 22 return intervals[i] - phase; 23 } 24 } 25 // If we get here, phase "appears" to be larger than our length. This 26 // shouldn't happen with perfect precision, but we can accumulate errors 27 // during the initial length computation (rounding can make our sum be too 28 // big or too small. In that event, we just have to eat the error here. 29 *index = 0; 30 return intervals[0]; 31} 32 33void SkDashPath::CalcDashParameters(SkScalar phase, const SkScalar intervals[], int32_t count, 34 SkScalar* initialDashLength, int32_t* initialDashIndex, 35 SkScalar* intervalLength, SkScalar* adjustedPhase) { 36 SkScalar len = 0; 37 for (int i = 0; i < count; i++) { 38 len += intervals[i]; 39 } 40 *intervalLength = len; 41 42 // watch out for values that might make us go out of bounds 43 if ((len > 0) && SkScalarIsFinite(phase) && SkScalarIsFinite(len)) { 44 45 // Adjust phase to be between 0 and len, "flipping" phase if negative. 46 // e.g., if len is 100, then phase of -20 (or -120) is equivalent to 80 47 if (adjustedPhase) { 48 if (phase < 0) { 49 phase = -phase; 50 if (phase > len) { 51 phase = SkScalarMod(phase, len); 52 } 53 phase = len - phase; 54 55 // Due to finite precision, it's possible that phase == len, 56 // even after the subtract (if len >>> phase), so fix that here. 57 // This fixes http://crbug.com/124652 . 58 SkASSERT(phase <= len); 59 if (phase == len) { 60 phase = 0; 61 } 62 } else if (phase >= len) { 63 phase = SkScalarMod(phase, len); 64 } 65 *adjustedPhase = phase; 66 } 67 SkASSERT(phase >= 0 && phase < len); 68 69 *initialDashLength = find_first_interval(intervals, phase, 70 initialDashIndex, count); 71 72 SkASSERT(*initialDashLength >= 0); 73 SkASSERT(*initialDashIndex >= 0 && *initialDashIndex < count); 74 } else { 75 *initialDashLength = -1; // signal bad dash intervals 76 } 77} 78 79static void outset_for_stroke(SkRect* rect, const SkStrokeRec& rec) { 80 SkScalar radius = SkScalarHalf(rec.getWidth()); 81 if (0 == radius) { 82 radius = SK_Scalar1; // hairlines 83 } 84 if (SkPaint::kMiter_Join == rec.getJoin()) { 85 radius = SkScalarMul(radius, rec.getMiter()); 86 } 87 rect->outset(radius, radius); 88} 89 90// Only handles lines for now. If returns true, dstPath is the new (smaller) 91// path. If returns false, then dstPath parameter is ignored. 92static bool cull_path(const SkPath& srcPath, const SkStrokeRec& rec, 93 const SkRect* cullRect, SkScalar intervalLength, 94 SkPath* dstPath) { 95 if (NULL == cullRect) { 96 return false; 97 } 98 99 SkPoint pts[2]; 100 if (!srcPath.isLine(pts)) { 101 return false; 102 } 103 104 SkRect bounds = *cullRect; 105 outset_for_stroke(&bounds, rec); 106 107 SkScalar dx = pts[1].x() - pts[0].x(); 108 SkScalar dy = pts[1].y() - pts[0].y(); 109 110 // just do horizontal lines for now (lazy) 111 if (dy) { 112 return false; 113 } 114 115 SkScalar minX = pts[0].fX; 116 SkScalar maxX = pts[1].fX; 117 118 if (maxX < bounds.fLeft || minX > bounds.fRight) { 119 return false; 120 } 121 122 if (dx < 0) { 123 SkTSwap(minX, maxX); 124 } 125 126 // Now we actually perform the chop, removing the excess to the left and 127 // right of the bounds (keeping our new line "in phase" with the dash, 128 // hence the (mod intervalLength). 129 130 if (minX < bounds.fLeft) { 131 minX = bounds.fLeft - SkScalarMod(bounds.fLeft - minX, 132 intervalLength); 133 } 134 if (maxX > bounds.fRight) { 135 maxX = bounds.fRight + SkScalarMod(maxX - bounds.fRight, 136 intervalLength); 137 } 138 139 SkASSERT(maxX >= minX); 140 if (dx < 0) { 141 SkTSwap(minX, maxX); 142 } 143 pts[0].fX = minX; 144 pts[1].fX = maxX; 145 146 dstPath->moveTo(pts[0]); 147 dstPath->lineTo(pts[1]); 148 return true; 149} 150 151class SpecialLineRec { 152public: 153 bool init(const SkPath& src, SkPath* dst, SkStrokeRec* rec, 154 int intervalCount, SkScalar intervalLength) { 155 if (rec->isHairlineStyle() || !src.isLine(fPts)) { 156 return false; 157 } 158 159 // can relax this in the future, if we handle square and round caps 160 if (SkPaint::kButt_Cap != rec->getCap()) { 161 return false; 162 } 163 164 SkScalar pathLength = SkPoint::Distance(fPts[0], fPts[1]); 165 166 fTangent = fPts[1] - fPts[0]; 167 if (fTangent.isZero()) { 168 return false; 169 } 170 171 fPathLength = pathLength; 172 fTangent.scale(SkScalarInvert(pathLength)); 173 fTangent.rotateCCW(&fNormal); 174 fNormal.scale(SkScalarHalf(rec->getWidth())); 175 176 // now estimate how many quads will be added to the path 177 // resulting segments = pathLen * intervalCount / intervalLen 178 // resulting points = 4 * segments 179 180 SkScalar ptCount = SkScalarMulDiv(pathLength, 181 SkIntToScalar(intervalCount), 182 intervalLength); 183 int n = SkScalarCeilToInt(ptCount) << 2; 184 dst->incReserve(n); 185 186 // we will take care of the stroking 187 rec->setFillStyle(); 188 return true; 189 } 190 191 void addSegment(SkScalar d0, SkScalar d1, SkPath* path) const { 192 SkASSERT(d0 < fPathLength); 193 // clamp the segment to our length 194 if (d1 > fPathLength) { 195 d1 = fPathLength; 196 } 197 198 SkScalar x0 = fPts[0].fX + SkScalarMul(fTangent.fX, d0); 199 SkScalar x1 = fPts[0].fX + SkScalarMul(fTangent.fX, d1); 200 SkScalar y0 = fPts[0].fY + SkScalarMul(fTangent.fY, d0); 201 SkScalar y1 = fPts[0].fY + SkScalarMul(fTangent.fY, d1); 202 203 SkPoint pts[4]; 204 pts[0].set(x0 + fNormal.fX, y0 + fNormal.fY); // moveTo 205 pts[1].set(x1 + fNormal.fX, y1 + fNormal.fY); // lineTo 206 pts[2].set(x1 - fNormal.fX, y1 - fNormal.fY); // lineTo 207 pts[3].set(x0 - fNormal.fX, y0 - fNormal.fY); // lineTo 208 209 path->addPoly(pts, SK_ARRAY_COUNT(pts), false); 210 } 211 212private: 213 SkPoint fPts[2]; 214 SkVector fTangent; 215 SkVector fNormal; 216 SkScalar fPathLength; 217}; 218 219 220bool SkDashPath::FilterDashPath(SkPath* dst, const SkPath& src, SkStrokeRec* rec, 221 const SkRect* cullRect, const SkScalar aIntervals[], 222 int32_t count, SkScalar initialDashLength, int32_t initialDashIndex, 223 SkScalar intervalLength) { 224 225 // we do nothing if the src wants to be filled, or if our dashlength is 0 226 if (rec->isFillStyle() || initialDashLength < 0) { 227 return false; 228 } 229 230 const SkScalar* intervals = aIntervals; 231 SkScalar dashCount = 0; 232 int segCount = 0; 233 234 SkPath cullPathStorage; 235 const SkPath* srcPtr = &src; 236 if (cull_path(src, *rec, cullRect, intervalLength, &cullPathStorage)) { 237 srcPtr = &cullPathStorage; 238 } 239 240 SpecialLineRec lineRec; 241 bool specialLine = lineRec.init(*srcPtr, dst, rec, count >> 1, intervalLength); 242 243 SkPathMeasure meas(*srcPtr, false); 244 245 do { 246 bool skipFirstSegment = meas.isClosed(); 247 bool addedSegment = false; 248 SkScalar length = meas.getLength(); 249 int index = initialDashIndex; 250 251 // Since the path length / dash length ratio may be arbitrarily large, we can exert 252 // significant memory pressure while attempting to build the filtered path. To avoid this, 253 // we simply give up dashing beyond a certain threshold. 254 // 255 // The original bug report (http://crbug.com/165432) is based on a path yielding more than 256 // 90 million dash segments and crashing the memory allocator. A limit of 1 million 257 // segments seems reasonable: at 2 verbs per segment * 9 bytes per verb, this caps the 258 // maximum dash memory overhead at roughly 17MB per path. 259 static const SkScalar kMaxDashCount = 1000000; 260 dashCount += length * (count >> 1) / intervalLength; 261 if (dashCount > kMaxDashCount) { 262 dst->reset(); 263 return false; 264 } 265 266 // Using double precision to avoid looping indefinitely due to single precision rounding 267 // (for extreme path_length/dash_length ratios). See test_infinite_dash() unittest. 268 double distance = 0; 269 double dlen = initialDashLength; 270 271 while (distance < length) { 272 SkASSERT(dlen >= 0); 273 addedSegment = false; 274 if (is_even(index) && dlen > 0 && !skipFirstSegment) { 275 addedSegment = true; 276 ++segCount; 277 278 if (specialLine) { 279 lineRec.addSegment(SkDoubleToScalar(distance), 280 SkDoubleToScalar(distance + dlen), 281 dst); 282 } else { 283 meas.getSegment(SkDoubleToScalar(distance), 284 SkDoubleToScalar(distance + dlen), 285 dst, true); 286 } 287 } 288 distance += dlen; 289 290 // clear this so we only respect it the first time around 291 skipFirstSegment = false; 292 293 // wrap around our intervals array if necessary 294 index += 1; 295 SkASSERT(index <= count); 296 if (index == count) { 297 index = 0; 298 } 299 300 // fetch our next dlen 301 dlen = intervals[index]; 302 } 303 304 // extend if we ended on a segment and we need to join up with the (skipped) initial segment 305 if (meas.isClosed() && is_even(initialDashIndex) && 306 initialDashLength > 0) { 307 meas.getSegment(0, initialDashLength, dst, !addedSegment); 308 ++segCount; 309 } 310 } while (meas.nextContour()); 311 312 if (segCount > 1) { 313 dst->setConvexity(SkPath::kConcave_Convexity); 314 } 315 316 return true; 317} 318 319bool SkDashPath::FilterDashPath(SkPath* dst, const SkPath& src, SkStrokeRec* rec, 320 const SkRect* cullRect, const SkPathEffect::DashInfo& info) { 321 SkScalar initialDashLength = 0; 322 int32_t initialDashIndex = 0; 323 SkScalar intervalLength = 0; 324 CalcDashParameters(info.fPhase, info.fIntervals, info.fCount, 325 &initialDashLength, &initialDashIndex, &intervalLength); 326 return FilterDashPath(dst, src, rec, cullRect, info.fIntervals, info.fCount, initialDashLength, 327 initialDashIndex, intervalLength); 328} 329