SPE-1720 Fix slowdown of long segments which cross small overhang area.

src/libslic3r/GCode/ExtrusionProcessor.hpp

@@ -274,21 +274,53 @@ public:
             const ExtendedPoint &curr = extended_points[i];
             const ExtendedPoint &next = extended_points[i + 1 < extended_points.size() ? i + 1 : i];
 
+            // The following code artifically increases the distance to provide slowdown for extrusions that are over curled lines
             float artificial_distance_to_curled_lines = 0.0;
+            const double dist_limit = 10.0 * path.width;
             {
                 Vec2d middle = 0.5 * (curr.position + next.position);
-                auto  line_indices = prev_curled_extrusions[current_object].all_lines_in_radius(Point::new_scale(middle),
+                auto line_indices = prev_curled_extrusions[current_object].all_lines_in_radius(Point::new_scale(middle), scale_(dist_limit));
-                                                                                                scale_(10.0 * path.width));
+                if (!line_indices.empty()) {
+                    double len   = (next.position - curr.position).norm();
+                    // For long lines, there is a problem with the additional slowdown. If by accident, there is small curled line near the middle of this long line
+                    //  The whole segment gets slower unnecesarily. For these long lines, we do additional check whether it is worth slowing down.
+                    // NOTE that this is still quite rough approximation, e.g. we are still checking lines only near the middle point
+                    // TODO maybe split the lines into smaller segments before running this alg? but can be demanding, and GCode will be huge
+                    if (len > 8) {
+                        Vec2d dir   = Vec2d(next.position - curr.position) / len;
+                        Vec2d right = Vec2d(-dir.y(), dir.x());
+
+                        Polygon box_of_influence = {
+                            scaled(Vec2d(curr.position + right * dist_limit)),
+                            scaled(Vec2d(next.position + right * dist_limit)),
+                            scaled(Vec2d(next.position - right * dist_limit)),
+                            scaled(Vec2d(curr.position - right * dist_limit)),
+                        };
+
+                        double projected_lengths_sum = 0;
+                        for (size_t idx : line_indices) {
+                            const CurledLine &line   = prev_curled_extrusions[current_object].get_line(idx);
+                            Lines             inside = intersection_ln({{line.a, line.b}}, {box_of_influence});
+                            if (inside.empty())
+                                continue;
+                            double projected_length = abs(dir.dot(unscaled(Vec2d((inside.back().b - inside.back().a).cast<double>()))));
+                            projected_lengths_sum += projected_length;
+                        }
+                        if (projected_lengths_sum < 0.4 * len) {
+                            line_indices.clear();
+                        }
+                    }
 
                     for (size_t idx : line_indices) {
                         const CurledLine &line                 = prev_curled_extrusions[current_object].get_line(idx);
                         float             distance_from_curled = unscaled(line_alg::distance_to(line, Point::new_scale(middle)));
-                    float             dist                 = path.width * (1.0 - (distance_from_curled / (10.0 * path.width))) *
+                        float             dist                 = path.width * (1.0 - (distance_from_curled / dist_limit)) *
-                                 (1.0 - (distance_from_curled / (10.0 * path.width))) *
+                                     (1.0 - (distance_from_curled / dist_limit)) *
                                      (line.curled_height / (path.height * 10.0f)); // max_curled_height_factor from SupportSpotGenerator
                         artificial_distance_to_curled_lines = std::max(artificial_distance_to_curled_lines, dist);
                     }
                 }
+            }
 
             auto interpolate_speed = [](const std::map<float, float> &values, float distance) {
                 auto upper_dist = values.lower_bound(distance);