Refactoring of EdgeGrid to accept an segment to segment visitor.

WIP: PolygonTrimmer to trim skirt & brim with polygons stored in EdgeGrid.

src/libslic3r/PolygonTrimmer.cpp

@@ -0,0 +1,56 @@
+#include "PolygonTrimmer.hpp"
+#include "EdgeGrid.hpp"
+#include "Geometry.hpp"
+
+namespace Slic3r {
+
+TrimmedLoop trim_loop(const Polygon &loop, const EdgeGrid::Grid &grid)
+{
+	assert(! loop.empty());
+	assert(loop.size() >= 2);
+
+	TrimmedLoop out;
+
+	if (loop.size() >= 2) {
+		size_t cnt = loop.points.size();
+
+		struct Visitor {
+			Visitor(const EdgeGrid::Grid &grid, const Slic3r::Point *pt_prev, const Slic3r::Point *pt_this) : grid(grid), pt_prev(pt_prev), pt_this(pt_this) {}
+
+			void operator()(coord_t iy, coord_t ix) {
+				// Called with a row and colum of the grid cell, which is intersected by a line.
+				auto cell_data_range = grid.cell_data_range(iy, ix);
+				for (auto it_contour_and_segment = cell_data_range.first; it_contour_and_segment != cell_data_range.second; ++ it_contour_and_segment) {
+					// End points of the line segment and their vector.
+					auto segment = grid.segment(*it_contour_and_segment);
+					if (Geometry::segments_intersect(segment.first, segment.second, *pt_prev, *pt_this)) {
+						// The two segments intersect. Add them to the output.
+					}
+				}
+			}
+
+			const EdgeGrid::Grid &grid;
+			const Slic3r::Point  *pt_this;
+			const Slic3r::Point  *pt_prev;
+		} visitor(grid, &loop.points.back(), nullptr);
+
+		for (const Point &pt_this : loop.points) {
+			visitor.pt_this = &pt_this;
+			grid.visit_cells_intersecting_line(*visitor.pt_prev, pt_this, visitor);
+			visitor.pt_prev = &pt_this;
+		}
+	}
+
+	return out;
+}
+
+std::vector<TrimmedLoop> trim_loops(const Polygons &loops, const EdgeGrid::Grid &grid)
+{
+	std::vector<TrimmedLoop> out;
+	out.reserve(loops.size());
+	for (const Polygon &loop : loops)
+		out.emplace_back(trim_loop(loop, grid));
+	return out;
+}
+
+}