static void scanConvert(const WFMath::Polygon<2>& inPoly, Surface& sf)
{
if (!inPoly.isValid()) return;
std::list<Edge> pending;
std::vector<Edge> active;
Point2 lastPt = inPoly.getCorner(inPoly.numCorners() - 1);
for (std::size_t p=0; p < inPoly.numCorners(); ++p) {
Point2 curPt = inPoly.getCorner(p);
// skip horizontal edges
if (curPt.y() != lastPt.y())
pending.emplace_back(lastPt, curPt);
lastPt = curPt;
}
if (pending.empty()) return;
// sort edges by starting (lowest) z value
pending.sort();
active.push_back(pending.front());
pending.pop_front();
// advance to the row of the first z value, and ensure z sits in the
// middle of sample rows - we do this by offseting by 1/2 a row height
// if you don't do this, you'll find alternating rows are over/under
// sampled, producing a charming striped effect.
WFMath::CoordType z = std::floor(active.front().start().y()) + ROW_HEIGHT * 0.5f;
for (; !pending.empty() || !active.empty(); z += ROW_HEIGHT)
{
while (!pending.empty() && (pending.front().start().y() <= z)) {
active.push_back(pending.front());
pending.pop_front();
}
// sort by x value - note active will be close to sorted anyway
std::sort(active.begin(), active.end(), EdgeAtZ(z));
// delete finished edges
for (unsigned int i=0; i< active.size(); ) {
if (active[i].end().y() <= z)
active.erase(active.begin() + i);
else
++i;
}
// draw pairs of active edges
for (unsigned int i=1; i < active.size(); i += 2)
span(sf, z, active[i - 1].xValueAtZ(z), active[i].xValueAtZ(z));
} // of active edges loop
}
WFMath::Polygon<2> sutherlandHodgmanKernel(const WFMath::Polygon<2>& inpoly, Clip clipper)
{
WFMath::Polygon<2> outpoly;
if (!inpoly.isValid()) return inpoly;
std::size_t points = inpoly.numCorners();
if (points < 3) return outpoly; // i.e an invalid result
Point2 lastPt = inpoly.getCorner(points - 1);
bool lastInside = clipper.inside(lastPt);
for (std::size_t p = 0; p < points; ++p) {
Point2 curPt = inpoly.getCorner(p);
bool inside = clipper.inside(curPt);
if (lastInside) {
if (inside) {
// emit curPt
outpoly.addCorner(outpoly.numCorners(), curPt);
} else {
// emit intersection of edge with clip line
outpoly.addCorner(outpoly.numCorners(), clipper.clip(lastPt, curPt));
}
} else {
if (inside) {
// emit both
outpoly.addCorner(outpoly.numCorners(), clipper.clip(lastPt, curPt));
outpoly.addCorner(outpoly.numCorners(), curPt);
} else {
// don't emit anything
}
} // last was outside
lastPt = curPt;
lastInside = inside;
}
return outpoly;
}