Improve fuzzy skin with modifier (#6759)

* Pass all compatible regions to perimeter generator

* Simplify & unify fuzzify detection

* Simplify `to_thick_polyline`

* Group regions by fuzzy skin settings

* Initial code structure of multi-regional fuzzy skin

* Determine fuzzy type by all compatible regions

* Add fuzzy region debug

* Implement the line split algorithm

* Do splitted fuzzy in classic mode

* Disable debug macros

* Fix infinit loop issue when segment points are out of order

* Fix path connection

* Implement splitted fuzzy in Arachne mode

src/libslic3r/Algorithm/LineSplit.hpp

@@ -0,0 +1,71 @@
+#ifndef SRC_LIBSLIC3R_ALGORITHM_LINE_SPLIT_HPP_
+#define SRC_LIBSLIC3R_ALGORITHM_LINE_SPLIT_HPP_
+
+#include "clipper2/clipper.core.h"
+#include "ClipperZUtils.hpp"
+
+namespace Slic3r {
+namespace Algorithm {
+
+struct SplitLineJunction
+{
+    Point p;
+
+    // true if the line between this point and the next point is inside the clip polygon (or on the edge of the clip polygon)
+    bool clipped;
+
+    // Index from the original input.
+    // - If this junction is presented in the source polygon/polyline, this is the index of the point with in the source;
+    // - if this point in a new point that caused by the intersection, this will be -(1+index of the first point of the source line involved in this intersection);
+    // - if this junction came from the clip polygon, it will be treated as new point.
+    int64_t src_idx;
+
+    SplitLineJunction(const Point& p, bool clipped, int64_t src_idx)
+        : p(p)
+        , clipped(clipped)
+        , src_idx(src_idx) {}
+
+    bool is_src() const { return src_idx >= 0; }
+    size_t get_src_index() const
+    {
+        if (is_src()) {
+            return src_idx;
+        } else {
+            return -src_idx - 1;
+        }
+    }
+};
+
+using SplittedLine = std::vector<SplitLineJunction>;
+
+SplittedLine do_split_line(const ClipperZUtils::ZPath& path, const ExPolygons& clip, bool closed);
+
+// Return the splitted line, or empty if no intersection found
+template<class PathType>
+SplittedLine split_line(const PathType& path, const ExPolygons& clip, bool closed)
+{
+    if (path.empty()) {
+        return {};
+    }
+
+    // Convert the input path into an open ZPath
+    ClipperZUtils::ZPath p;
+    p.reserve(path.size() + closed ? 1 : 0);
+    ClipperLib_Z::cInt z = 0;
+    for (const auto& point : path) {
+        p.emplace_back(point.x(), point.y(), z);
+        z++;
+    }
+    if (closed) {
+        // duplicate the first point at the end to make a closed path open
+        p.emplace_back(p.front());
+        p.back().z() = z;
+    }
+
+    return do_split_line(p, clip, closed);
+}
+
+} // Algorithm
+} // Slic3r
+
+#endif /* SRC_LIBSLIC3R_ALGORITHM_LINE_SPLIT_HPP_ */