int SkIntersections::vertical(const SkDLine& line, double top, double bottom,
double x, bool flipped) {
fMax = 3; // cleanup parallel lines will bring this back line
// see if end points intersect the opposite line
double t;
SkDPoint topPt = { x, top };
if ((t = line.exactPoint(topPt)) >= 0) {
insert(t, (double) flipped, topPt);
}
if (top != bottom) {
SkDPoint bottomPt = { x, bottom };
if ((t = line.exactPoint(bottomPt)) >= 0) {
insert(t, (double) !flipped, bottomPt);
}
for (int index = 0; index < 2; ++index) {
if ((t = SkDLine::ExactPointV(line[index], top, bottom, x)) >= 0) {
insert((double) index, flipped ? 1 - t : t, line[index]);
}
}
}
int result = vertical_coincident(line, x);
if (result == 1 && fUsed == 0) {
fT[0][0] = VerticalIntercept(line, x);
double yIntercept = line[0].fY + fT[0][0] * (line[1].fY - line[0].fY);
if (between(top, yIntercept, bottom)) {
fT[1][0] = (yIntercept - top) / (bottom - top);
if (flipped) {
// OPTIMIZATION: instead of swapping, pass original line, use [1].fY - [0].fY
for (int index = 0; index < result; ++index) {
fT[1][index] = 1 - fT[1][index];
}
}
fPt[0].fX = x;
fPt[0].fY = yIntercept;
fUsed = 1;
}
}
if (fAllowNear || result == 2) {
if ((t = line.nearPoint(topPt, nullptr)) >= 0) {
insert(t, (double) flipped, topPt);
}
if (top != bottom) {
SkDPoint bottomPt = { x, bottom };
if ((t = line.nearPoint(bottomPt, nullptr)) >= 0) {
insert(t, (double) !flipped, bottomPt);
}
for (int index = 0; index < 2; ++index) {
if ((t = SkDLine::NearPointV(line[index], top, bottom, x)) >= 0) {
insert((double) index, flipped ? 1 - t : t, line[index]);
}
}
}
}
cleanUpParallelLines(result == 2);
SkASSERT(fUsed <= 2);
return fUsed;
}
int SkIntersections::horizontal(const SkDLine& line, double left, double right,
double y, bool flipped) {
fMax = 3; // clean up parallel at the end will limit the result to 2 at the most
// see if end points intersect the opposite line
double t;
const SkDPoint leftPt = { left, y };
if ((t = line.exactPoint(leftPt)) >= 0) {
insert(t, (double) flipped, leftPt);
}
if (left != right) {
const SkDPoint rightPt = { right, y };
if ((t = line.exactPoint(rightPt)) >= 0) {
insert(t, (double) !flipped, rightPt);
}
for (int index = 0; index < 2; ++index) {
if ((t = SkDLine::ExactPointH(line[index], left, right, y)) >= 0) {
insert((double) index, flipped ? 1 - t : t, line[index]);
}
}
}
int result = horizontal_coincident(line, y);
if (result == 1 && fUsed == 0) {
fT[0][0] = HorizontalIntercept(line, y);
double xIntercept = line[0].fX + fT[0][0] * (line[1].fX - line[0].fX);
if (between(left, xIntercept, right)) {
fT[1][0] = (xIntercept - left) / (right - left);
if (flipped) {
// OPTIMIZATION: ? instead of swapping, pass original line, use [1].fX - [0].fX
for (int index = 0; index < result; ++index) {
fT[1][index] = 1 - fT[1][index];
}
}
fPt[0].fX = xIntercept;
fPt[0].fY = y;
fUsed = 1;
}
}
if (fAllowNear || result == 2) {
if ((t = line.nearPoint(leftPt, nullptr)) >= 0) {
insert(t, (double) flipped, leftPt);
}
if (left != right) {
const SkDPoint rightPt = { right, y };
if ((t = line.nearPoint(rightPt, nullptr)) >= 0) {
insert(t, (double) !flipped, rightPt);
}
for (int index = 0; index < 2; ++index) {
if ((t = SkDLine::NearPointH(line[index], left, right, y)) >= 0) {
insert((double) index, flipped ? 1 - t : t, line[index]);
}
}
}
}
cleanUpParallelLines(result == 2);
return fUsed;
}
// note that this only works if both lines are neither horizontal nor vertical
int SkIntersections::intersect(const SkDLine& a, const SkDLine& b) {
fMax = 3; // note that we clean up so that there is no more than two in the end
// see if end points intersect the opposite line
double t;
for (int iA = 0; iA < 2; ++iA) {
if ((t = b.exactPoint(a[iA])) >= 0) {
insert(iA, t, a[iA]);
}
}
for (int iB = 0; iB < 2; ++iB) {
if ((t = a.exactPoint(b[iB])) >= 0) {
insert(t, iB, b[iB]);
}
}
/* Determine the intersection point of two line segments
Return FALSE if the lines don't intersect
from: http://paulbourke.net/geometry/lineline2d/ */
double axLen = a[1].fX - a[0].fX;
double ayLen = a[1].fY - a[0].fY;
double bxLen = b[1].fX - b[0].fX;
double byLen = b[1].fY - b[0].fY;
/* Slopes match when denom goes to zero:
axLen / ayLen == bxLen / byLen
(ayLen * byLen) * axLen / ayLen == (ayLen * byLen) * bxLen / byLen
byLen * axLen == ayLen * bxLen
byLen * axLen - ayLen * bxLen == 0 ( == denom )
*/
double axByLen = axLen * byLen;
double ayBxLen = ayLen * bxLen;
// detect parallel lines the same way here and in SkOpAngle operator <
// so that non-parallel means they are also sortable
bool unparallel = fAllowNear ? NotAlmostEqualUlps(axByLen, ayBxLen)
: NotAlmostDequalUlps(axByLen, ayBxLen);
if (unparallel && fUsed == 0) {
double ab0y = a[0].fY - b[0].fY;
double ab0x = a[0].fX - b[0].fX;
double numerA = ab0y * bxLen - byLen * ab0x;
double numerB = ab0y * axLen - ayLen * ab0x;
double denom = axByLen - ayBxLen;
if (between(0, numerA, denom) && between(0, numerB, denom)) {
fT[0][0] = numerA / denom;
fT[1][0] = numerB / denom;
computePoints(a, 1);
}
}
/* Allow tracking that both sets of end points are near each other -- the lines are entirely
coincident -- even when the end points are not exactly the same.
Mark this as a 'wild card' for the end points, so that either point is considered totally
coincident. Then, avoid folding the lines over each other, but allow either end to mate
to the next set of lines.
*/
if (fAllowNear || !unparallel) {
double aNearB[2];
double bNearA[2];
bool aNotB[2] = {false, false};
bool bNotA[2] = {false, false};
int nearCount = 0;
for (int index = 0; index < 2; ++index) {
aNearB[index] = t = b.nearPoint(a[index], &aNotB[index]);
nearCount += t >= 0;
bNearA[index] = t = a.nearPoint(b[index], &bNotA[index]);
nearCount += t >= 0;
}
if (nearCount > 0) {
// Skip if each segment contributes to one end point.
if (nearCount != 2 || aNotB[0] == aNotB[1]) {
for (int iA = 0; iA < 2; ++iA) {
if (!aNotB[iA]) {
continue;
}
int nearer = aNearB[iA] > 0.5;
if (!bNotA[nearer]) {
continue;
}
SkASSERT(a[iA] != b[nearer]);
SkASSERT(iA == (bNearA[nearer] > 0.5));
insertNear(iA, nearer, a[iA], b[nearer]);
aNearB[iA] = -1;
bNearA[nearer] = -1;
nearCount -= 2;
}
}
if (nearCount > 0) {
for (int iA = 0; iA < 2; ++iA) {
if (aNearB[iA] >= 0) {
insert(iA, aNearB[iA], a[iA]);
}
}
for (int iB = 0; iB < 2; ++iB) {
if (bNearA[iB] >= 0) {
insert(bNearA[iB], iB, b[iB]);
}
}
}
}
}
cleanUpParallelLines(!unparallel);
SkASSERT(fUsed <= 2);
return fUsed;
}