SkVector SkEvalQuadTangentAt(const SkPoint src[3], SkScalar t) {
SkASSERT(src);
SkASSERT(t >= 0 && t <= SK_Scalar1);
Sk2s P0 = from_point(src[0]);
Sk2s P1 = from_point(src[1]);
Sk2s P2 = from_point(src[2]);
Sk2s B = P1 - P0;
Sk2s A = P2 - P1 - B;
Sk2s T = A * Sk2s(t) + B;
return to_vector(T + T);
}
SkVector SkEvalQuadTangentAt(const SkPoint src[3], SkScalar t) {
// The derivative equation is 2(b - a +(a - 2b +c)t). This returns a
// zero tangent vector when t is 0 or 1, and the control point is equal
// to the end point. In this case, use the quad end points to compute the tangent.
if ((t == 0 && src[0] == src[1]) || (t == 1 && src[1] == src[2])) {
return src[2] - src[0];
}
SkASSERT(src);
SkASSERT(t >= 0 && t <= SK_Scalar1);
Sk2s P0 = from_point(src[0]);
Sk2s P1 = from_point(src[1]);
Sk2s P2 = from_point(src[2]);
Sk2s B = P1 - P0;
Sk2s A = P2 - P1 - B;
Sk2s T = A * Sk2s(t) + B;
return to_vector(T + T);
}
