Fix bug in cubic derivative coefficient with missing parens

src/utils/SkCurveMeasure.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkCurveMeasure.h"
 #include "SkGeometry.h"
 
@@ skipping 112 matching lines @@
             float By = pts[1].y();
             float Cy = pts[2].y();
             float Dy = pts[3].y();
 
             // precompute coefficients for derivative
             xCoeff[0] = Sk8f(3.0f*(-Ax + 3.0f*(Bx - Cx) + Dx));
             xCoeff[1] = Sk8f(3.0f*(2.0f*(Ax - 2.0f*Bx + Cx)));
             xCoeff[2] = Sk8f(3.0f*(-Ax + Bx));
 
             yCoeff[0] = Sk8f(3.0f*(-Ay + 3.0f*(By - Cy) + Dy));
-            yCoeff[1] = Sk8f(3.0f * -Ay + By + 2.0f*(Ay - 2.0f*By + Cy));
+            yCoeff[1] = Sk8f(3.0f*(2.0f*(Ay - 2.0f*By + Cy)));

[reed1, 2016/08/16 21:19:35]

this seems fine. two nits:

1. don't need 3.0f when 3 will do (I find the latter easier to parse)
2. for efficiency, seems better to resolve some of those constant*
expressions...
    6*(Ay - 2*By + Cy)

             yCoeff[2] = Sk8f(3.0f*(-Ay + By));
         }
             break;
         case kConic_SegType:
             UNIMPLEMENTED;
             break;
         default:
             UNIMPLEMENTED;
     }
 }
@@ skipping 157 matching lines @@
     if (time) {
         *time = t;
     }
     if (pos) {
         *pos = evaluate(fPts, fSegType, t);
     }
     if (tan) {
         *tan = evaluateDerivative(fPts, fSegType, t);
     }
 }