use Sk2s for EvalQuadTangent and ChopQuadAt

src/core/SkGeometry.cpp

Index: src/core/SkGeometry.cpp
diff --git a/src/core/SkGeometry.cpp b/src/core/SkGeometry.cpp
index 6d14e4bb54f595996213a85ecd08d4242f8c450c..2643c87c90dd6392b232897d2fdc87fde3df7ece 100644
--- a/src/core/SkGeometry.cpp
+++ b/src/core/SkGeometry.cpp
@@ -147,6 +147,23 @@ SkPoint SkEvalQuadAt(const SkPoint src[3], SkScalar t) {
     return result;
 }
 
+SkVector SkEvalQuadTangentAt(const SkPoint src[3], SkScalar t) {
+    SkASSERT(src);
+    SkASSERT(t >= 0 && t <= SK_Scalar1);
+
+    Sk2f P0 = Sk2f::Load(&src[0].fX);
+    Sk2f P1 = Sk2f::Load(&src[1].fX);
+    Sk2f P2 = Sk2f::Load(&src[2].fX);
+
+    Sk2f B = P1 - P0;
+    Sk2f A = P2 - P1 - B;
+    Sk2f T = A * Sk2f(t) + B;
+
+    SkVector result;
+    (T + T).store(&result.fX);
+    return result;
+}
+
 static void interp_quad_coords(const SkScalar* src, SkScalar* dst, SkScalar t) {
     SkScalar    ab = SkScalarInterp(src[0], src[2], t);
     SkScalar    bc = SkScalarInterp(src[2], src[4], t);
@@ -165,6 +182,28 @@ void SkChopQuadAt(const SkPoint src[3], SkPoint dst[5], SkScalar t) {
     interp_quad_coords(&src[0].fY, &dst[0].fY, t);
 }
 
+static Sk2s interp(Sk2s A, Sk2s B, Sk2s T) {

[mtklein, 2015/03/20 11:39:48]

Interesting.

The x86 Windows warnings are telling us it has no way to guarantee these
parameters will be passed with 16-byte alignment.  The x86-64 calling convention
requires these to pass by xmm registers, which is perfect, and other 32-bit
platforms probably 16-byte align the stack, which is fine, but here MSVC is
throwing up its hands and saying it can do neither.

Annoyingly, I think we have to write

static Sk2s interp(const Sk2s& A, const Sk2s& B, const Sk2s& T) {
   return A + (B - A) * T;
}

+    return A + (B - A) * T;
+}
+
+void SkChopQuadAt2(const SkPoint src[3], SkPoint dst[5], SkScalar t) {
+    SkASSERT(t > 0 && t < SK_Scalar1);
+
+    Sk2s P0 = Sk2f::Load(&src[0].fX);

[mtklein, 2015/03/20 11:39:48]

You might call these A,B,C to match AB and BC.

+    Sk2s P1 = Sk2f::Load(&src[1].fX);
+    Sk2s P2 = Sk2f::Load(&src[2].fX);
+    Sk2s tt = Sk2s(t);
+    
+    Sk2s AB = interp(P0, P1, tt);
+    Sk2s BC = interp(P1, P2, tt);
+
+    P0.store(&dst[0].fX);
+    AB.store(&dst[1].fX);
+    interp(AB, BC, tt).store(&dst[2].fX);
+    BC.store(&dst[3].fX);
+    P2.store(&dst[4].fX);
+}
+
 void SkChopQuadAtHalf(const SkPoint src[3], SkPoint dst[5]) {
     SkScalar x01 = SkScalarAve(src[0].fX, src[1].fX);
     SkScalar y01 = SkScalarAve(src[0].fY, src[1].fY);