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 "SkDiscretePathEffect.h" 11 #include "SkReadBuffer.h" 12 #include "SkWriteBuffer.h" 13 #include "SkPathMeasure.h" 14 #include "SkStrokeRec.h" 15 16 static void Perterb(SkPoint* p, const SkVector& tangent, SkScalar scale) { 17 SkVector normal = tangent; 18 normal.rotateCCW(); 19 normal.setLength(scale); 20 *p += normal; 21 } 22 23 SkDiscretePathEffect::SkDiscretePathEffect(SkScalar segLength, 24 SkScalar deviation, 25 uint32_t seedAssist) 26 : fSegLength(segLength), fPerterb(deviation), fSeedAssist(seedAssist) 27 { 28 } 29 30 /** \class LCGRandom 31 32 Utility class that implements pseudo random 32bit numbers using a fast 33 linear equation. Unlike rand(), this class holds its own seed (initially 34 set to 0), so that multiple instances can be used with no side-effects. 35 36 Copied from the original implementation of SkRandom. Only contains the 37 methods used by SkDiscretePathEffect::filterPath, with methods that were 38 not called directly moved to private. 39 */ 40 41 class LCGRandom { 42 public: 43 LCGRandom(uint32_t seed) : fSeed(seed) {} 44 45 /** Return the next pseudo random number expressed as a SkScalar 46 in the range (-SK_Scalar1..SK_Scalar1). 47 */ 48 SkScalar nextSScalar1() { return SkFixedToScalar(this->nextSFixed1()); } 49 50 private: 51 /** Return the next pseudo random number as an unsigned 32bit value. 52 */ 53 uint32_t nextU() { uint32_t r = fSeed * kMul + kAdd; fSeed = r; return r; } 54 55 /** Return the next pseudo random number as a signed 32bit value. 56 */ 57 int32_t nextS() { return (int32_t)this->nextU(); } 58 59 /** Return the next pseudo random number expressed as a signed SkFixed 60 in the range (-SK_Fixed1..SK_Fixed1). 61 */ 62 SkFixed nextSFixed1() { return this->nextS() >> 15; } 63 64 // See "Numerical Recipes in C", 1992 page 284 for these constants 65 enum { 66 kMul = 1664525, 67 kAdd = 1013904223 68 }; 69 uint32_t fSeed; 70 }; 71 72 bool SkDiscretePathEffect::filterPath(SkPath* dst, const SkPath& src, 73 SkStrokeRec* rec, const SkRect*) const { 74 bool doFill = rec->isFillStyle(); 75 76 SkPathMeasure meas(src, doFill); 77 78 /* Caller may supply their own seed assist, which by default is 0 */ 79 uint32_t seed = fSeedAssist ^ SkScalarRoundToInt(meas.getLength()); 80 81 LCGRandom rand(seed ^ ((seed << 16) | (seed >> 16))); 82 SkScalar scale = fPerterb; 83 SkPoint p; 84 SkVector v; 85 86 do { 87 SkScalar length = meas.getLength(); 88 89 if (fSegLength * (2 + doFill) > length) { 90 meas.getSegment(0, length, dst, true); // to short for us to mangle 91 } else { 92 int n = SkScalarRoundToInt(length / fSegLength); 93 SkScalar delta = length / n; 94 SkScalar distance = 0; 95 96 if (meas.isClosed()) { 97 n -= 1; 98 distance += delta/2; 99 } 100 101 if (meas.getPosTan(distance, &p, &v)) { 102 Perterb(&p, v, SkScalarMul(rand.nextSScalar1(), scale)); 103 dst->moveTo(p); 104 } 105 while (--n >= 0) { 106 distance += delta; 107 if (meas.getPosTan(distance, &p, &v)) { 108 Perterb(&p, v, SkScalarMul(rand.nextSScalar1(), scale)); 109 dst->lineTo(p); 110 } 111 } 112 if (meas.isClosed()) { 113 dst->close(); 114 } 115 } 116 } while (meas.nextContour()); 117 return true; 118 } 119 120 SkFlattenable* SkDiscretePathEffect::CreateProc(SkReadBuffer& buffer) { 121 SkScalar segLength = buffer.readScalar(); 122 SkScalar perterb = buffer.readScalar(); 123 uint32_t seed = buffer.readUInt(); 124 return Create(segLength, perterb, seed); 125 } 126 127 void SkDiscretePathEffect::flatten(SkWriteBuffer& buffer) const { 128 buffer.writeScalar(fSegLength); 129 buffer.writeScalar(fPerterb); 130 buffer.writeUInt(fSeedAssist); 131 } 132 133 #ifndef SK_IGNORE_TO_STRING 134 void SkDiscretePathEffect::toString(SkString* str) const { 135 str->appendf("SkDiscretePathEffect: ("); 136 str->appendf("segLength: %.2f deviation: %.2f seed %d", fSegLength, fPerterb, fSeedAssist); 137 str->append(")"); 138 } 139 #endif 140
