From c03085a1f679c1104f9ae09ecb66902ef6fe5cef Mon Sep 17 00:00:00 2001
From: Vojtech Bubnik <bubnikv@gmail.com>
Date: Thu, 18 Aug 2022 10:45:18 +0200
Subject: [PATCH] Performance improvement in G-code export for support material
 in suppression of retracts when traveling over support regions.

---
 src/libslic3r/GCode.cpp           | 29 ++++++++++++++++++++---------
 src/libslic3r/Layer.hpp           |  2 ++
 src/libslic3r/SupportMaterial.cpp |  9 +++++++--
 3 files changed, 29 insertions(+), 11 deletions(-)

diff --git a/src/libslic3r/GCode.cpp b/src/libslic3r/GCode.cpp
index d836ac43c..1ddee6b7c 100644
--- a/src/libslic3r/GCode.cpp
+++ b/src/libslic3r/GCode.cpp
@@ -3134,15 +3134,26 @@ bool GCode::needs_retraction(const Polyline &travel, ExtrusionRole role)
         return false;
     }
 
-    if (role == erSupportMaterial) {
-        const SupportLayer* support_layer = dynamic_cast<const SupportLayer*>(m_layer);
-        //FIXME support_layer->support_islands.contains should use some search structure!
-        if (support_layer != NULL && ! intersection_pl(travel, support_layer->support_islands).empty())
-            // skip retraction if this is a travel move inside a support material island
-            //FIXME not retracting over a long path may cause oozing, which in turn may result in missing material
-            // at the end of the extrusion path!
-            return false;
-    }
+    if (role == erSupportMaterial)
+        if (const SupportLayer *support_layer = dynamic_cast<const SupportLayer*>(m_layer);
+            support_layer != nullptr && ! support_layer->support_islands_bboxes.empty()) {
+            BoundingBox bbox_travel = get_extents(travel);
+            Polylines   trimmed;
+            bool        trimmed_initialized = false;
+            for (const BoundingBox &bbox : support_layer->support_islands_bboxes)
+                if (bbox.overlap(bbox_travel)) {
+                    const auto &island = support_layer->support_islands[&bbox - support_layer->support_islands_bboxes.data()];
+                    trimmed = trimmed_initialized ? diff_pl(trimmed, island) : diff_pl(travel, island);
+                    trimmed_initialized = true;
+                    if (trimmed.empty())
+                        // skip retraction if this is a travel move inside a support material island
+                        //FIXME not retracting over a long path may cause oozing, which in turn may result in missing material
+                        // at the end of the extrusion path!
+                        return false;
+                    // Not sure whether updating the boudning box isn't too expensive.
+                    //bbox_travel = get_extents(trimmed);
+                }
+        }
 
     if (m_config.only_retract_when_crossing_perimeters && m_layer != nullptr &&
         m_config.fill_density.value > 0 && m_layer->any_internal_region_slice_contains(travel))
diff --git a/src/libslic3r/Layer.hpp b/src/libslic3r/Layer.hpp
index 21de030cd..e11c740e6 100644
--- a/src/libslic3r/Layer.hpp
+++ b/src/libslic3r/Layer.hpp
@@ -197,6 +197,8 @@ public:
     // Polygons covered by the supports: base, interface and contact areas.
     // Used to suppress retraction if moving for a support extrusion over these support_islands.
     ExPolygons                  support_islands;
+    // Slightly inflated bounding boxes of the above, for faster intersection query.
+    std::vector<BoundingBox>    support_islands_bboxes;
     // Extrusion paths for the support base and for the support interface and contacts.
     ExtrusionEntityCollection   support_fills;
 
diff --git a/src/libslic3r/SupportMaterial.cpp b/src/libslic3r/SupportMaterial.cpp
index 340449ec8..0f704c3d6 100644
--- a/src/libslic3r/SupportMaterial.cpp
+++ b/src/libslic3r/SupportMaterial.cpp
@@ -4312,8 +4312,13 @@ void generate_support_toolpaths(
                 // Order the layers by lexicographically by an increasing print_z and a decreasing layer height.
                 std::stable_sort(layer_cache_item.overlapping.begin(), layer_cache_item.overlapping.end(), [](auto *l1, auto *l2) { return *l1 < *l2; });
             }
-            if (! polys.empty())
-                expolygons_append(support_layer.support_islands, union_ex(polys));
+            assert(support_layer.support_islands.empty());
+            if (! polys.empty()) {
+                support_layer.support_islands = union_ex(polys);
+                support_layer.support_islands_bboxes.reserve(support_layer.support_islands.size());
+                for (const ExPolygon &expoly : support_layer.support_islands)
+                    support_layer.support_islands_bboxes.emplace_back(get_extents(expoly).inflated(SCALED_EPSILON));
+            }
         } // for each support_layer_id
     });