Stub for conic section max curvature

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"
 
@@ skipping 1144 matching lines @@
     if (dir == kCCW_SkRotationDirection) {
         matrix.preScale(SK_Scalar1, -SK_Scalar1);
     }
     if (userMatrix) {
         matrix.postConcat(*userMatrix);
     }
     matrix.mapPoints(quadPoints, pointCount);
     return pointCount;
 }
 
+
 ///////////////////////////////////////////////////////////////////////////////
-
+//
+// NURB representation for conics.  Helpful explanations at:
+//
+// http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.44.5740&rep=rep1&type=ps

[reed1, 2014/02/21 17:00:04]

nit: 80-col

[humper, 2014/02/21 17:07:21]

Done, and fixed a bunch of other 80 col issues in this file.

+// and
+// http://www.cs.mtu.edu/~shene/COURSES/cs3621/NOTES/spline/NURBS/RB-conics.html
+//
 // F = (A (1 - t)^2 + C t^2 + 2 B (1 - t) t w)
 //     ------------------------------------------
 //         ((1 - t)^2 + t^2 + 2 (1 - t) t w)
 //
 //   = {t^2 (P0 + P2 - 2 P1 w), t (-2 P0 + 2 P1 w), P0}
 //     ------------------------------------------------
 //             {t^2 (2 - 2 w), t (-2 + 2 w), 1}
 //
 
-// Take the parametric specification for the conic (either X or Y) and return
-// in coeff[] the coefficients for the simple quadratic polynomial
-//    coeff[0] for t^2
-//    coeff[1] for t
-//    coeff[2] for constant term
-//
 static SkScalar conic_eval_pos(const SkScalar src[], SkScalar w, SkScalar t) {
     SkASSERT(src);
     SkASSERT(t >= 0 && t <= SK_Scalar1);
 
     SkScalar    src2w = SkScalarMul(src[2], w);
     SkScalar    C = src[0];
     SkScalar    A = src[4] - 2 * src2w + C;
     SkScalar    B = 2 * (src2w - C);
     SkScalar numer = SkScalarMulAdd(SkScalarMulAdd(A, t, B), t, C);
 
     B = 2 * (w - SK_Scalar1);
     C = SK_Scalar1;
     A = -B;
     SkScalar denom = SkScalarMulAdd(SkScalarMulAdd(A, t, B), t, C);
 
     return SkScalarDiv(numer, denom);
 }
 
+
+// Take the parametric specification for the conic (either X or Y) and return

[reed1, 2014/02/21 17:00:04]

This comment does not go with deriv_coeff, but perhaps there is no longer a
helper function that just returns the poly coeff for the conic?

[humper, 2014/02/21 17:07:21]

Done.

+// in coeff[] the coefficients for the simple quadratic polynomial
+//
 // F' = 2 (C t (1 + t (-1 + w)) - A (-1 + t) (t (-1 + w) - w) + B (1 - 2 t) w)
 //
 //  t^2 : (2 P0 - 2 P2 - 2 P0 w + 2 P2 w)
 //  t^1 : (-2 P0 + 2 P2 + 4 P0 w - 4 P1 w)
 //  t^0 : -2 P0 w + 2 P1 w
 //
 //  We disregard magnitude, so we can freely ignore the denominator of F', and
 //  divide the numerator by 2
 //
 //    coeff[0] for t^2
@@ skipping 225 matching lines @@
     }
     if (this->findYExtrema(&t)) {
         this->evalAt(t, &pts[count++]);
     }
     bounds->set(pts, count);
 }
 
 void SkConic::computeFastBounds(SkRect* bounds) const {
     bounds->set(fPts, 3);
 }
+
+// Find the parameter value where the conic takes on its maximum curvature.

[reed1, 2014/02/21 17:00:04]

Lets hoist this comment out to the header.

[humper, 2014/02/21 17:07:21]

Done.

+// Returns true if the max curvature is inside the 0..1 parameter range,
+// otherwise returns false and leaves its t parameter unchanged.
+bool SkConic::findMaxCurvature(SkScalar* t) const {
+    // TODO: Implement me
+    return false;
+}