The Tor Browser / file diff

     1.1 --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
     1.2 +++ b/gfx/skia/trunk/src/utils/SkCubicInterval.cpp	Wed Dec 31 06:09:35 2014 +0100
     1.3 @@ -0,0 +1,67 @@
     1.4 +
     1.5 +/*
     1.6 + * Copyright 2011 Google Inc.
     1.7 + *
     1.8 + * Use of this source code is governed by a BSD-style license that can be
     1.9 + * found in the LICENSE file.
    1.10 + */
    1.11 +#include "SkCubicInterval.h"
    1.12 +
    1.13 +static SkScalar eval_cubic(SkScalar c1, SkScalar c2, SkScalar c3,
    1.14 +                           SkScalar t) {
    1.15 +    return SkScalarMul(SkScalarMul(SkScalarMul(c3, t) + c2, t) + c1, t);
    1.16 +}
    1.17 +
    1.18 +static SkScalar find_cubic_t(SkScalar c1, SkScalar c2, SkScalar c3,
    1.19 +                             SkScalar targetX) {
    1.20 +    SkScalar minT = 0;
    1.21 +    SkScalar maxT = SK_Scalar1;
    1.22 +    SkScalar t;
    1.23 +
    1.24 +    for (;;) {
    1.25 +        t = SkScalarAve(minT, maxT);
    1.26 +        SkScalar x = eval_cubic(c1, c2, c3, t);
    1.27 +        if (SkScalarNearlyZero(x - targetX)) {
    1.28 +            break;
    1.29 +        }
    1.30 +        // subdivide the range and try again
    1.31 +        if (x < targetX) {
    1.32 +            minT = t;
    1.33 +        } else {
    1.34 +            maxT = t;
    1.35 +        }
    1.36 +    }
    1.37 +    return t;
    1.38 +}
    1.39 +
    1.40 +/*
    1.41 +    a(1-t)^3 + 3bt(1-t)^2 + 3ct^2(1-t) + dt^3
    1.42 +    a: [0, 0]
    1.43 +    d: [1, 1]
    1.44 +
    1.45 +    3bt - 6bt^2 + 3bt^3 + 3ct^2 - 3ct^3 + t^3
    1.46 +    C1 = t^1: 3b
    1.47 +    C2 = t^2: 3c - 6b
    1.48 +    C3 = t^3: 3b - 3c + 1
    1.49 +
    1.50 +    ((C3*t + C2)*t + C1)*t
    1.51 + */
    1.52 +SkScalar SkEvalCubicInterval(SkScalar x1, SkScalar y1,
    1.53 +                             SkScalar x2, SkScalar y2,
    1.54 +                             SkScalar unitX) {
    1.55 +    x1 = SkScalarPin(x1, 0, SK_Scalar1);
    1.56 +    x2 = SkScalarPin(x2, 0, SK_Scalar1);
    1.57 +    unitX = SkScalarPin(unitX, 0, SK_Scalar1);
    1.58 +
    1.59 +    // First compute our coefficients in X
    1.60 +    x1 *= 3;
    1.61 +    x2 *= 3;
    1.62 +
    1.63 +    // now search for t given unitX
    1.64 +    SkScalar t = find_cubic_t(x1, x2 - 2*x1, x1 - x2 + SK_Scalar1, unitX);
    1.65 +
    1.66 +    // now evaluate the cubic in Y
    1.67 +    y1 *= 3;
    1.68 +    y2 *= 3;
    1.69 +    return eval_cubic(y1, y2 - 2*y1, y1 - y2 + SK_Scalar1, t);
    1.70 +}