// This is a safe variant of the polygon offset, tailored for a single ExPolygon:
// a single polygon with multiple non-overlapping holes.
// Each contour and hole is offsetted separately, then the holes are subtracted from the outer contours.
ClipperLib::Paths _offset(const Slic3r::ExPolygon &expolygon, const float delta,
ClipperLib::JoinType joinType, double miterLimit)
{
// printf("new ExPolygon offset\n");
// 1) Offset the outer contour.
const float delta_scaled = delta * float(CLIPPER_OFFSET_SCALE);
ClipperLib::Paths contours;
{
ClipperLib::Path input = Slic3rMultiPoint_to_ClipperPath(expolygon.contour);
scaleClipperPolygon(input);
ClipperLib::ClipperOffset co;
if (joinType == jtRound)
co.ArcTolerance = miterLimit * double(CLIPPER_OFFSET_SCALE);
else
co.MiterLimit = miterLimit;
co.ShortestEdgeLength = double(std::abs(delta_scaled * CLIPPER_OFFSET_SHORTEST_EDGE_FACTOR));
co.AddPath(input, joinType, ClipperLib::etClosedPolygon);
co.Execute(contours, delta_scaled);
}
// 2) Offset the holes one by one, collect the results.
ClipperLib::Paths holes;
{
holes.reserve(expolygon.holes.size());
for (Polygons::const_iterator it_hole = expolygon.holes.begin(); it_hole != expolygon.holes.end(); ++ it_hole) {
ClipperLib::Path input = Slic3rMultiPoint_to_ClipperPath_reversed(*it_hole);
scaleClipperPolygon(input);
ClipperLib::ClipperOffset co;
if (joinType == jtRound)
co.ArcTolerance = miterLimit * double(CLIPPER_OFFSET_SCALE);
else
co.MiterLimit = miterLimit;
co.ShortestEdgeLength = double(std::abs(delta_scaled * CLIPPER_OFFSET_SHORTEST_EDGE_FACTOR));
co.AddPath(input, joinType, ClipperLib::etClosedPolygon);
ClipperLib::Paths out;
co.Execute(out, - delta_scaled);
holes.insert(holes.end(), out.begin(), out.end());
}
}
// 3) Subtract holes from the contours.
ClipperLib::Paths output;
if (holes.empty()) {
output = std::move(contours);
} else {
ClipperLib::Clipper clipper;
clipper.Clear();
clipper.AddPaths(contours, ClipperLib::ptSubject, true);
clipper.AddPaths(holes, ClipperLib::ptClip, true);
clipper.Execute(ClipperLib::ctDifference, output, ClipperLib::pftNonZero, ClipperLib::pftNonZero);
}
// 4) Unscale the output.
unscaleClipperPolygons(output);
return output;
}
// This is a safe variant of the polygon offset, tailored for a single ExPolygon:
// a single polygon with multiple non-overlapping holes.
// Each contour and hole is offsetted separately, then the holes are subtracted from the outer contours.
void offset(const Slic3r::ExPolygons &expolygons, ClipperLib::Paths* retval, const float delta,
ClipperLib::JoinType joinType, double miterLimit)
{
// printf("new ExPolygon offset\n");
const float delta_scaled = delta * float(CLIPPER_OFFSET_SCALE);
ClipperLib::Paths contours;
ClipperLib::Paths holes;
contours.reserve(expolygons.size());
{
size_t n_holes = 0;
for (size_t i = 0; i < expolygons.size(); ++ i)
n_holes += expolygons[i].holes.size();
holes.reserve(n_holes);
}
for (Slic3r::ExPolygons::const_iterator it_expoly = expolygons.begin(); it_expoly != expolygons.end(); ++ it_expoly) {
// 1) Offset the outer contour.
{
ClipperLib::Path input;
Slic3rMultiPoint_to_ClipperPath(it_expoly->contour, &input);
scaleClipperPolygon(input);
ClipperLib::ClipperOffset co;
if (joinType == jtRound)
co.ArcTolerance = miterLimit * double(CLIPPER_OFFSET_SCALE);
else
co.MiterLimit = miterLimit;
co.AddPath(input, joinType, ClipperLib::etClosedPolygon);
ClipperLib::Paths out;
co.Execute(out, delta_scaled);
contours.insert(contours.end(), out.begin(), out.end());
}
// 2) Offset the holes one by one, collect the results.
{
for (Polygons::const_iterator it_hole = it_expoly->holes.begin(); it_hole != it_expoly->holes.end(); ++ it_hole) {
ClipperLib::Path input;
Slic3rMultiPoint_to_ClipperPath_reversed(*it_hole, &input);
scaleClipperPolygon(input);
ClipperLib::ClipperOffset co;
if (joinType == jtRound)
co.ArcTolerance = miterLimit * double(CLIPPER_OFFSET_SCALE);
else
co.MiterLimit = miterLimit;
co.AddPath(input, joinType, ClipperLib::etClosedPolygon);
ClipperLib::Paths out;
co.Execute(out, - delta_scaled);
holes.insert(holes.end(), out.begin(), out.end());
}
}
}
// 3) Subtract holes from the contours.
ClipperLib::Paths output;
{
ClipperLib::Clipper clipper;
clipper.Clear();
clipper.AddPaths(contours, ClipperLib::ptSubject, true);
clipper.AddPaths(holes, ClipperLib::ptClip, true);
clipper.Execute(ClipperLib::ctDifference, *retval, ClipperLib::pftNonZero, ClipperLib::pftNonZero);
}
// 4) Unscale the output.
unscaleClipperPolygons(*retval);
}
// This is a safe variant of the polygons offset, tailored for multiple ExPolygons.
// It is required, that the input expolygons do not overlap and that the holes of each ExPolygon don't intersect with their respective outer contours.
// Each ExPolygon is offsetted separately, then the offsetted ExPolygons are united.
ClipperLib::Paths _offset(const Slic3r::ExPolygons &expolygons, const float delta,
ClipperLib::JoinType joinType, double miterLimit)
{
const float delta_scaled = delta * float(CLIPPER_OFFSET_SCALE);
// Offsetted ExPolygons before they are united.
ClipperLib::Paths contours_cummulative;
contours_cummulative.reserve(expolygons.size());
// How many non-empty offsetted expolygons were actually collected into contours_cummulative?
// If only one, then there is no need to do a final union.
size_t expolygons_collected = 0;
for (Slic3r::ExPolygons::const_iterator it_expoly = expolygons.begin(); it_expoly != expolygons.end(); ++ it_expoly) {
// 1) Offset the outer contour.
ClipperLib::Paths contours;
{
ClipperLib::Path input = Slic3rMultiPoint_to_ClipperPath(it_expoly->contour);
scaleClipperPolygon(input);
ClipperLib::ClipperOffset co;
if (joinType == jtRound)
co.ArcTolerance = miterLimit * double(CLIPPER_OFFSET_SCALE);
else
co.MiterLimit = miterLimit;
co.ShortestEdgeLength = double(std::abs(delta_scaled * CLIPPER_OFFSET_SHORTEST_EDGE_FACTOR));
co.AddPath(input, joinType, ClipperLib::etClosedPolygon);
co.Execute(contours, delta_scaled);
}
if (contours.empty())
// No need to try to offset the holes.
continue;
if (it_expoly->holes.empty()) {
// No need to subtract holes from the offsetted expolygon, we are done.
contours_cummulative.insert(contours_cummulative.end(), contours.begin(), contours.end());
++ expolygons_collected;
} else {
// 2) Offset the holes one by one, collect the offsetted holes.
ClipperLib::Paths holes;
{
for (Polygons::const_iterator it_hole = it_expoly->holes.begin(); it_hole != it_expoly->holes.end(); ++ it_hole) {
ClipperLib::Path input = Slic3rMultiPoint_to_ClipperPath_reversed(*it_hole);
scaleClipperPolygon(input);
ClipperLib::ClipperOffset co;
if (joinType == jtRound)
co.ArcTolerance = miterLimit * double(CLIPPER_OFFSET_SCALE);
else
co.MiterLimit = miterLimit;
co.ShortestEdgeLength = double(std::abs(delta_scaled * CLIPPER_OFFSET_SHORTEST_EDGE_FACTOR));
co.AddPath(input, joinType, ClipperLib::etClosedPolygon);
ClipperLib::Paths out;
co.Execute(out, - delta_scaled);
holes.insert(holes.end(), out.begin(), out.end());
}
}
// 3) Subtract holes from the contours.
if (holes.empty()) {
// No hole remaining after an offset. Just copy the outer contour.
contours_cummulative.insert(contours_cummulative.end(), contours.begin(), contours.end());
++ expolygons_collected;
} else if (delta < 0) {
// Negative offset. There is a chance, that the offsetted hole intersects the outer contour.
// Subtract the offsetted holes from the offsetted contours.
ClipperLib::Clipper clipper;
clipper.Clear();
clipper.AddPaths(contours, ClipperLib::ptSubject, true);
clipper.AddPaths(holes, ClipperLib::ptClip, true);
ClipperLib::Paths output;
clipper.Execute(ClipperLib::ctDifference, output, ClipperLib::pftNonZero, ClipperLib::pftNonZero);
if (! output.empty()) {
contours_cummulative.insert(contours_cummulative.end(), output.begin(), output.end());
++ expolygons_collected;
} else {
// The offsetted holes have eaten up the offsetted outer contour.
}
} else {
// Positive offset. As long as the Clipper offset does what one expects it to do, the offsetted hole will have a smaller
// area than the original hole or even disappear, therefore there will be no new intersections.
// Just collect the reversed holes.
contours_cummulative.reserve(contours.size() + holes.size());
contours_cummulative.insert(contours_cummulative.end(), contours.begin(), contours.end());
// Reverse the holes in place.
for (size_t i = 0; i < holes.size(); ++ i)
std::reverse(holes[i].begin(), holes[i].end());
contours_cummulative.insert(contours_cummulative.end(), holes.begin(), holes.end());
++ expolygons_collected;
}
}
}
// 4) Unite the offsetted expolygons.
ClipperLib::Paths output;
if (expolygons_collected > 1 && delta > 0) {
// There is a chance that the outwards offsetted expolygons may intersect. Perform a union.
ClipperLib::Clipper clipper;
clipper.Clear();
clipper.AddPaths(contours_cummulative, ClipperLib::ptSubject, true);
clipper.Execute(ClipperLib::ctUnion, output, ClipperLib::pftNonZero, ClipperLib::pftNonZero);
} else {
// Negative offset. The shrunk expolygons shall not mutually intersect. Just copy the output.
output = std::move(contours_cummulative);
}
// 4) Unscale the output.
unscaleClipperPolygons(output);
return output;
}