cc: Replace the WebCore::UnitBezier class with the SkUnitCubicInterp() method from Skia.

cc/timing_function.cc

Index: cc/timing_function.cc
diff --git a/cc/timing_function.cc b/cc/timing_function.cc
index 6588d36d9649c51aa57bce41f1832389a638ced5..50b0a32c06feeb97677885a28fc91e0898211c9e 100644
--- a/cc/timing_function.cc
+++ b/cc/timing_function.cc
@@ -5,10 +5,78 @@
 #include "config.h"
 
 #include "cc/timing_function.h"
+#include "third_party/skia/include/core/SkMath.h"
 
+// TODO(danakj) These methods come from SkInterpolator.cpp. When such a method
+// is available in the public Skia API, we should switch to using that.

[jamesr, 2012/11/06 23:21:19]

can we have a bug for this?

[danakj, 2012/11/06 23:26:51]

Ya, I had asked mike for one, but I'll just make one.

 namespace {
-const double epsilon = 1e-6;
-} // namespace
+
+// Dot14 has 14 bits for decimal places, and the remainder for whole numbers.
+typedef int Dot14;
+#define DOT14_ONE       (1 << 14)
+#define DOT14_HALF      (1 << 13)
+
+#define Dot14ToFloat(x) ((x) / 16384.f)
+
+static inline Dot14 Dot14Mul(Dot14 a, Dot14 b)
+{
+    return (a * b + DOT14_HALF) >> 14;
+}
+
+static inline Dot14 EvalCubic(Dot14 t, Dot14 A, Dot14 B, Dot14 C)
+{
+    return Dot14Mul(Dot14Mul(Dot14Mul(C, t) + B, t) + A, t);
+}
+
+static inline Dot14 PinAndConvert(SkScalar x)
+{
+    if (x <= 0)
+        return 0;
+    if (x >= SK_Scalar1)
+        return DOT14_ONE;
+    return SkScalarToFixed(x) >> 2;
+}
+
+SkScalar SkUnitCubicInterp(SkScalar bx, SkScalar by, SkScalar cx, SkScalar cy, SkScalar value)
+{
+    Dot14 x = PinAndConvert(value);
+
+    if (x == 0) return 0;
+    if (x == DOT14_ONE) return SK_Scalar1;
+
+    Dot14 b = PinAndConvert(bx);
+    Dot14 c = PinAndConvert(cx);
+
+    // Now compute our coefficients from the control points.
+    //  t   -> 3b
+    //  t^2 -> 3c - 6b
+    //  t^3 -> 3b - 3c + 1
+    Dot14 A = 3 * b;
+    Dot14 B = 3 * (c - 2 * b);
+    Dot14 C = 3 * (b - c) + DOT14_ONE;
+
+    // Now search for a t value given x.
+    Dot14 t = DOT14_HALF;
+    Dot14 dt = DOT14_HALF;
+    for (int i = 0; i < 13; i++) {
+        dt >>= 1;
+        Dot14 guess = EvalCubic(t, A, B, C);
+        if (x < guess)
+            t -= dt;
+        else
+            t += dt;
+    }
+
+    // Now we have t, so compute the coefficient for Y and evaluate.
+    b = PinAndConvert(by);
+    c = PinAndConvert(cy);
+    A = 3 * b;
+    B = 3 * (c - 2 * b);
+    C = 3 * (b - c) + DOT14_ONE;
+    return SkFixedToScalar(EvalCubic(t, A, B, C) << 2);
+}
+
+}  // anonymous namespace
 
 namespace cc {
 
@@ -31,7 +99,10 @@ scoped_ptr<CubicBezierTimingFunction> CubicBezierTimingFunction::create(double x
 }
 
 CubicBezierTimingFunction::CubicBezierTimingFunction(double x1, double y1, double x2, double y2)
-    : m_curve(x1, y1, x2, y2)
+    : m_x1(SkDoubleToScalar(x1))
+    , m_y1(SkDoubleToScalar(y1))
+    , m_x2(SkDoubleToScalar(x2))
+    , m_y2(SkDoubleToScalar(y2))
 {
 }
 
@@ -41,8 +112,8 @@ CubicBezierTimingFunction::~CubicBezierTimingFunction()
 
 float CubicBezierTimingFunction::getValue(double x) const
 {
-    UnitBezier temp(m_curve);
-    return static_cast<float>(temp.solve(x, epsilon));
+    SkScalar value = SkUnitCubicInterp(m_x1, m_y1, m_x2, m_y2, x);
+    return SkScalarToFloat(value);
 }
 
 scoped_ptr<AnimationCurve> CubicBezierTimingFunction::clone() const