1 /* 2 * Copyright 2016 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 #ifndef SkCurveMeasure_DEFINED 9 #define SkCurveMeasure_DEFINED 10 11 #include "SkPathMeasurePriv.h" 12 #include "SkPoint.h" 13 #include "SkNx.h" 14 15 // These are weights and abscissae for gaussian quadrature with weight function 16 // w(x) = 1 17 static SkScalar weights8[8] = {0.3626837833783620f, 0.3626837833783620f, 18 0.3137066458778873f, 0.3137066458778873f, 19 0.2223810344533745f, 0.2223810344533745f, 20 0.1012285362903763f, 0.1012285362903763f}; 21 static SkScalar absc8[8] = {-0.1834346424956498f, 0.1834346424956498f, 22 -0.5255324099163290f, 0.5255324099163290f, 23 -0.7966664774136267f, 0.7966664774136267f, 24 -0.9602898564975363f, 0.9602898564975363f}; 25 26 static Sk8f weights = Sk8f::Load(weights8); 27 static Sk8f absc = 0.5f*(Sk8f::Load(absc8) + 1.0f); 28 29 30 class ArcLengthIntegrator { 31 public: ArcLengthIntegrator()32 ArcLengthIntegrator() {} 33 ArcLengthIntegrator(const SkPoint* pts, SkSegType segType); 34 SkScalar computeLength(SkScalar t); 35 36 private: 37 SkSegType fSegType; 38 39 // precomputed coefficients for derivatives in Horner form 40 float xCoeff[3][8]; 41 float yCoeff[3][8]; 42 }; 43 44 class SkCurveMeasure { 45 public: SkCurveMeasure()46 SkCurveMeasure() {} 47 48 // Almost exactly the same as in SkPath::Iter: 49 // kLine_SegType -> 2 points: start end 50 // kQuad_SegType -> 3 points: start control end 51 // kCubic_SegType -> 4 points: start control1 control2 end 52 // kConic_SegType -> 4 points: start control end (w, w) 53 // 54 // i.e. the only difference is that the conic's last point is a point 55 // consisting of the w value twice 56 SkCurveMeasure(const SkPoint* pts, SkSegType segType); 57 58 SkScalar getTime(SkScalar targetLength); 59 void getPosTanTime(SkScalar distance, SkPoint* pos, SkVector* tan, SkScalar* time); 60 SkScalar getLength(); 61 62 private: 63 const SkScalar kTolerance = 0.0001f; 64 const int kNewtonIters = 5; 65 const int kBisectIters = 5; 66 67 SkSegType fSegType; 68 SkPoint fPts[4]; 69 SkScalar fLength = -1.0f; 70 ArcLengthIntegrator fIntegrator; 71 72 // for debug purposes 73 int fIters; 74 }; 75 76 #endif // SkCurveMeasure_DEFINED 77