Implement Conics in SkCurveMeasure

src/utils/SkCurveMeasure.h

Index: src/utils/SkCurveMeasure.h
diff --git a/src/utils/SkCurveMeasure.h b/src/utils/SkCurveMeasure.h
index 5807211236efbe96d146eff421f096e5697e7957..eaf779db8de7883343e67d50dcb4a87199ab06a2 100644
--- a/src/utils/SkCurveMeasure.h
+++ b/src/utils/SkCurveMeasure.h
@@ -14,18 +14,26 @@
 
 // These are weights and abscissae for gaussian quadrature with weight function
 // w(x) = 1
-static SkScalar weights8[8] = {0.3626837833783620f, 0.3626837833783620f,
-                               0.3137066458778873f, 0.3137066458778873f,
-                               0.2223810344533745f, 0.2223810344533745f,
-                               0.1012285362903763f, 0.1012285362903763f};
-static SkScalar absc8[8] = {-0.1834346424956498f, 0.1834346424956498f,
-                            -0.5255324099163290f, 0.5255324099163290f,
-                            -0.7966664774136267f, 0.7966664774136267f,
-                            -0.9602898564975363f, 0.9602898564975363f};
+static const SkScalar weights8[8] = {0.3626837833783620f, 0.3626837833783620f,
+                                     0.3137066458778873f, 0.3137066458778873f,
+                                     0.2223810344533745f, 0.2223810344533745f,
+                                     0.1012285362903763f, 0.1012285362903763f};
+static const SkScalar absc8[8] = {-0.1834346424956498f, 0.1834346424956498f,
+                                  -0.5255324099163290f, 0.5255324099163290f,
+                                  -0.7966664774136267f, 0.7966664774136267f,
+                                  -0.9602898564975363f, 0.9602898564975363f};
 
-static Sk8f weights = Sk8f::Load(weights8);
-static Sk8f absc = 0.5f*(Sk8f::Load(absc8) + 1.0f);
+static const Sk8f weights = Sk8f::Load(weights8);
+static const Sk8f absc = 0.5f*(Sk8f::Load(absc8) + 1.0f);
 
+/* Currently this uses Gaussian quadrature with a fixed number of
+ * evaluation points (see above weights and abscissae) but in principle
+ * we could have a table of abscissae and weights and choose which to use
+ * based on an approximation of the max length of the curve.
+ *
+ * We should always use some power of 2 number of evaluation points so that
+ * the SkNx templates will compile down into SIMD-register-aligned blocks.
+ */
 
 class ArcLengthIntegrator {
 public:
@@ -37,14 +45,14 @@ private:
     SkSegType fSegType;
 
     // precomputed coefficients for derivatives in Horner form
-    Sk8f xCoeff[3];
-    Sk8f yCoeff[3];
+    Sk8f fXCoeff[3];
+    Sk8f fYCoeff[3];
+
+    SkScalar fConicW = 0;
 };
 
 class SkCurveMeasure {
 public:
-    SkCurveMeasure() {}
-
     // Almost exactly the same as in SkPath::Iter:
     // kLine_SegType  -> 2 points: start end
     // kQuad_SegType  -> 3 points: start control end
@@ -60,9 +68,9 @@ public:
     SkScalar getLength();
 
 private:
-    const SkScalar kTolerance = 0.0001f;
-    const int kNewtonIters = 5;
-    const int kBisectIters = 5;
+    static constexpr SkScalar kTolerance = 0.0001f;
+    static const int kNewtonIters = 5;
+    static const int kBisectIters = 5;
 
     SkSegType fSegType;
     SkPoint fPts[4];