commit 17bc0851d34afe8c89d7455c061a1d419f76af8a
author caryclark <caryclark@google.com> Mon Dec 21 05:32:53 2015 -0800
committer Commit bot <commit-bot@chromium.org> Mon Dec 21 05:32:53 2015 -0800
tree 6b68edd6ec8d32fe7c3c13ff6943e94df3ef8385
parent dd180e795fcdf0ff424e753c7a822fad1ca8a700

check in direct quad length measure

Add code so that it at minimum won't bit-rot.
Next: add tests to see if it works.

R=reed@google.com
BUG=skia:1036
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1541523002

Review URL: https://codereview.chromium.org/1541523002

src/core/SkPathMeasure.cpp

diff --git a/src/core/SkPathMeasure.cpp b/src/core/SkPathMeasure.cpp
index d959f45..eb80cf3 100644
--- a/src/core/SkPathMeasure.cpp
+++ b/src/core/SkPathMeasure.cpp
@@ -90,6 +90,28 @@
                          SkScalarInterp(pts[0].fY, pts[3].fY, SK_Scalar1*2/3));
 }
 
+/* from http://www.malczak.linuxpl.com/blog/quadratic-bezier-curve-length/ */
+static SkScalar compute_quad_len(const SkPoint pts[3]) {
+     SkPoint a,b;
+     a.fX = pts[0].fX - 2 * pts[1].fX + pts[2].fX;
+     a.fY = pts[0].fY - 2 * pts[1].fY + pts[2].fY;
+     b.fX = 2 * (pts[1].fX - pts[0].fX);
+     b.fY = 2 * (pts[1].fY - pts[0].fY);
+     SkScalar A = 4 * (a.fX * a.fX + a.fY * a.fY);
+     SkScalar B = 4 * (a.fX * b.fX + a.fY * b.fY);
+     SkScalar C =      b.fX * b.fX + b.fY * b.fY;
+
+     SkScalar Sabc = 2 * SkScalarSqrt(A + B + C);
+     SkScalar A_2  = SkScalarSqrt(A);
+     SkScalar A_32 = 2 * A * A_2;
+     SkScalar C_2  = 2 * SkScalarSqrt(C);
+     SkScalar BA   = B / A_2;
+
+     return (A_32 * Sabc + A_2 * B * (Sabc - C_2) +
+            (4 * C * A - B * B) * SkScalarLog((2 * A_2 + BA + Sabc) / (BA + C_2))) / (4 * A_32);
+}
+
+
 SkScalar SkPathMeasure::compute_quad_segs(const SkPoint pts[3],
                           SkScalar distance, int mint, int maxt, int ptIndex) {
     if (tspan_big_enough(maxt - mint) && quad_too_curvy(pts)) {
@@ -209,7 +231,19 @@
 
             case SkPath::kQuad_Verb: {
                 SkScalar prevD = distance;
-                distance = this->compute_quad_segs(pts, distance, 0, kMaxTValue, ptIndex);
+                if (false) {
+                    SkScalar length = compute_quad_len(pts);
+                    if (length) {
+                        distance += length;
+                        Segment* seg = fSegments.append();
+                        seg->fDistance = distance;
+                        seg->fPtIndex = ptIndex;
+                        seg->fType = kQuad_SegType;
+                        seg->fTValue = kMaxTValue;
+                    }
+                } else {
+                    distance = this->compute_quad_segs(pts, distance, 0, kMaxTValue, ptIndex);
+                }
                 if (distance > prevD) {
                     fPts.append(2, pts + 1);
                     ptIndex += 2;