SkScalar SkPoint::distanceToLineSegmentBetweenSqd(const SkPoint& a,
const SkPoint& b) const {
// See comments to distanceToLineBetweenSqd. If the projection of c onto
// u is between a and b then this returns the same result as that
// function. Otherwise, it returns the distance to the closer of a and
// b. Let the projection of v onto u be v'. There are three cases:
// 1. v' points opposite to u. c is not between a and b and is closer
// to a than b.
// 2. v' points along u and has magnitude less than y. c is between
// a and b and the distance to the segment is the same as distance
// to the line ab.
// 3. v' points along u and has greater magnitude than u. c is not
// not between a and b and is closer to b than a.
// v' = (u dot v) * u / |u|. So if (u dot v)/|u| is less than zero we're
// in case 1. If (u dot v)/|u| is > |u| we are in case 3. Otherwise
// we're in case 2. We actually compare (u dot v) to 0 and |u|^2 to
// avoid a sqrt to compute |u|.
SkVector u = b - a;
SkVector v = *this - a;
SkScalar uLengthSqd = u.lengthSqd();
SkScalar uDotV = SkPoint::DotProduct(u, v);
if (uDotV <= 0) {
return v.lengthSqd();
} else if (uDotV > uLengthSqd) {
return b.distanceToSqd(*this);
} else {
SkScalar det = u.cross(v);
return SkScalarMulDiv(det, det, uLengthSqd);
}
}
static void test_conic_tangents(skiatest::Reporter* reporter) {
SkPoint pts[] = {
{ 10, 20}, {10, 20}, {20, 30},
{ 10, 20}, {15, 25}, {20, 30},
{ 10, 20}, {20, 30}, {20, 30}
};
int count = (int) SK_ARRAY_COUNT(pts) / 3;
for (int index = 0; index < count; ++index) {
SkConic conic(&pts[index * 3], 0.707f);
SkVector start = conic.evalTangentAt(0);
SkVector mid = conic.evalTangentAt(.5f);
SkVector end = conic.evalTangentAt(1);
REPORTER_ASSERT(reporter, start.fX && start.fY);
REPORTER_ASSERT(reporter, mid.fX && mid.fY);
REPORTER_ASSERT(reporter, end.fX && end.fY);
REPORTER_ASSERT(reporter, SkScalarNearlyZero(start.cross(mid)));
REPORTER_ASSERT(reporter, SkScalarNearlyZero(mid.cross(end)));
}
}
// Compute the intersection 'p' between segments s0 and s1, if any.
// 's' is the parametric value for the intersection along 's0' & 't' is the same for 's1'.
// Returns false if there is no intersection.
static bool compute_intersection(const InsetSegment& s0, const InsetSegment& s1,
SkPoint* p, SkScalar* s, SkScalar* t) {
SkVector v0 = s0.fP1 - s0.fP0;
SkVector v1 = s1.fP1 - s1.fP0;
SkScalar perpDot = v0.cross(v1);
if (SkScalarNearlyZero(perpDot)) {
// segments are parallel
// check if endpoints are touching
if (s0.fP1.equalsWithinTolerance(s1.fP0)) {
*p = s0.fP1;
*s = SK_Scalar1;
*t = 0;
return true;
}
if (s1.fP1.equalsWithinTolerance(s0.fP0)) {
*p = s1.fP1;
*s = 0;
*t = SK_Scalar1;
return true;
}
return false;
}
SkVector d = s1.fP0 - s0.fP0;
SkScalar localS = d.cross(v1) / perpDot;
if (localS < 0 || localS > SK_Scalar1) {
return false;
}
SkScalar localT = d.cross(v0) / perpDot;
if (localT < 0 || localT > SK_Scalar1) {
return false;
}
v0 *= localS;
*p = s0.fP0 + v0;
*s = localS;
*t = localT;
return true;
}
SkScalar SkPoint::distanceToLineBetweenSqd(const SkPoint& a,
const SkPoint& b,
Side* side) const {
SkVector u = b - a;
SkVector v = *this - a;
SkScalar uLengthSqd = u.lengthSqd();
SkScalar det = u.cross(v);
if (side) {
SkASSERT(-1 == SkPoint::kLeft_Side &&
0 == SkPoint::kOn_Side &&
1 == kRight_Side);
*side = (Side) SkScalarSignAsInt(det);
}
return SkScalarMulDiv(det, det, uLengthSqd);
}
static bool is_clockwise(const SkVector& before, const SkVector& after) {
return before.cross(after) > 0;
}
