fix circular dashing

src/core/SkGeometry.cpp

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkGeometry.h"
 #include "SkMatrix.h"
 #include "SkNx.h"
 
-#if 0
-static Sk2s from_point(const SkPoint& point) {
-    return Sk2s::Load(&point.fX);
-}
-
-static SkPoint to_point(const Sk2s& x) {
-    SkPoint point;
-    x.store(&point.fX);
-    return point;
-}
-#endif
-
 static SkVector to_vector(const Sk2s& x) {
     SkVector vector;
     x.store(&vector.fX);
     return vector;
 }
 
 /** If defined, this makes eval_quad and eval_cubic do more setup (sometimes
     involving integer multiplies by 2 or 3, but fewer calls to SkScalarMul.
     May also introduce overflow of fixed when we compute our setup.
 */
@@ skipping 179 matching lines @@
     Sk2s p12 = interp(p1, p2, tt);
 
     dst[0] = to_point(p0);
     dst[1] = to_point(p01);
     dst[2] = to_point(interp(p01, p12, tt));
     dst[3] = to_point(p12);
     dst[4] = to_point(p2);
 }
 
 void SkChopQuadAtHalf(const SkPoint src[3], SkPoint dst[5]) {
-    SkChopQuadAt(src, dst, 0.5f); return;
+    SkChopQuadAt(src, dst, 0.5f);
 }
 
 /** Quad'(t) = At + B, where
     A = 2(a - 2b + c)
     B = 2(b - a)
     Solve for t, only if it fits between 0 < t < 1
 */
 int SkFindQuadExtrema(SkScalar a, SkScalar b, SkScalar c, SkScalar tValue[1]) {
     /*  At + B == 0
         t = -B / A
@@ skipping 1005 matching lines @@
     // w1 /= sqrt(w0*w2)
     //
     // However, in our case, we know that for dst[0]:
     //     w0 == 1, and for dst[1], w2 == 1
     //
     SkScalar root = SkScalarSqrt(tmp2[1].fZ);
     dst[0].fW = tmp2[0].fZ / root;
     dst[1].fW = tmp2[2].fZ / root;
 }
 
-static Sk2s times_2(const Sk2s& value) {
-    return value + value;
+void SkConic::chopAt(SkScalar t1, SkScalar t2, SkConic* dst) const {
+    if (0 == t1 || 1 == t2) {
+        if (0 == t1 && 1 == t2) {
+            *dst = *this;
+        } else {
+            SkConic pair[2];
+            this->chopAt(t1 ? t1 : t2, pair);
+            *dst = pair[SkToBool(t1)];
+        }
+        return;
+    }
+    SkConicCoeff coeff(*this);
+    Sk2s tt1(t1);
+    Sk2s aXY = coeff.fNumer.eval(tt1);
+    Sk2s aZZ = coeff.fDenom.eval(tt1);
+    Sk2s midTT((t1 + t2) / 2);
+    Sk2s dXY = coeff.fNumer.eval(midTT);
+    Sk2s dZZ = coeff.fDenom.eval(midTT);
+    Sk2s tt2(t2);
+    Sk2s cXY = coeff.fNumer.eval(tt2);
+    Sk2s cZZ = coeff.fDenom.eval(tt2);
+    Sk2s bXY = times_2(dXY) - (aXY + cXY) * Sk2s(0.5f);
+    Sk2s bZZ = times_2(dZZ) - (aZZ + cZZ) * Sk2s(0.5f);
+    dst->fPts[0] = to_point(aXY / aZZ);
+    dst->fPts[1] = to_point(bXY / bZZ);
+    dst->fPts[2] = to_point(cXY / cZZ);
+    Sk2s ww = bZZ / (aZZ * cZZ).sqrt();
+    dst->fW = ww.kth<0>();
 }
 
 SkPoint SkConic::evalAt(SkScalar t) const {
     Sk2s p0 = from_point(fPts[0]);
     Sk2s p1 = from_point(fPts[1]);
     Sk2s p2 = from_point(fPts[2]);
     Sk2s tt(t);
     Sk2s ww(fW);
     Sk2s one(1);
 
@@ skipping 316 matching lines @@
         matrix.preScale(SK_Scalar1, -SK_Scalar1);
     }
     if (userMatrix) {
         matrix.postConcat(*userMatrix);
     }
     for (int i = 0; i < conicCount; ++i) {
         matrix.mapPoints(dst[i].fPts, 3);
     }
     return conicCount;
 }