Added invalidation of the sliced object when gap-fill enabled/disabled if the object is painted using the multi-material painting gizmo.

Filtering of unprintable regions in multi-material segmentation depends on if gap-fill is enabled or not. So sliced object is invalidated when gap-fill was enabled/disabled by option "gap_fill_enabled" or by changing "gap_fill_speed" to force recomputation of the multi-material segmentation.

src/libslic3r/Model.cpp

@@ -725,6 +725,11 @@ void ModelObject::clear_volumes()
     this->invalidate_bounding_box();
 }
 
+bool ModelObject::is_mm_painted() const
+{
+    return std::any_of(this->volumes.cbegin(), this->volumes.cend(), [](const ModelVolume *mv) { return mv->is_mm_painted(); });
+}
+
 void ModelObject::sort_volumes(bool full_sort)
 {
     // sort volumes inside the object to order "Model Part, Negative Volume, Modifier, Support Blocker and Support Enforcer. "

src/libslic3r/Model.hpp

@@ -285,6 +285,8 @@ public:
     void                    clear_volumes();
     void                    sort_volumes(bool full_sort);
     bool                    is_multiparts() const { return volumes.size() > 1; }
+    // Checks if any of object volume is painted using the multi-material painting gizmo.
+    bool                    is_mm_painted() const;
 
     ModelInstance*          add_instance();
     ModelInstance*          add_instance(const ModelInstance &instance);
@@ -715,6 +717,8 @@ public:
         this->mmu_segmentation_facets.set_new_unique_id();
     }
 
+    bool is_mm_painted() const { return !this->mmu_segmentation_facets.empty(); }
+
 protected:
 	friend class Print;
     friend class SLAPrint;

src/libslic3r/Print.hpp

@@ -317,6 +317,8 @@ public:
     bool                        has_support()           const { return m_config.support_material || m_config.support_material_enforce_layers > 0; }
     bool                        has_raft()              const { return m_config.raft_layers > 0; }
     bool                        has_support_material()  const { return this->has_support() || this->has_raft(); }
+    // Checks if the model object is painted using the multi-material painting gizmo.
+    bool                        is_mm_painted()         const { return this->model_object()->is_mm_painted(); };
 
     // returns 0-based indices of extruders used to print the object (without brim, support and other helper extrusions)
     std::vector<unsigned int>   object_extruders() const;

src/libslic3r/PrintObject.cpp

@@ -509,13 +509,32 @@ bool PrintObject::invalidate_state_by_config_options(
         } else if (
                opt_key == "perimeters"
             || opt_key == "extra_perimeters"
-            || opt_key == "gap_fill_enabled"
-            || opt_key == "gap_fill_speed"
             || opt_key == "first_layer_extrusion_width"
             || opt_key == "perimeter_extrusion_width"
             || opt_key == "infill_overlap"
             || opt_key == "external_perimeters_first") {
             steps.emplace_back(posPerimeters);
+        } else if (
+               opt_key == "gap_fill_enabled"
+            || opt_key == "gap_fill_speed") {
+            // Return true if gap-fill speed has changed from zero value to non-zero or from non-zero value to zero.
+            auto is_gap_fill_changed_state_due_to_speed = [&opt_key, &old_config, &new_config]() -> bool {
+                if (opt_key == "gap_fill_speed") {
+                    const auto *old_gap_fill_speed = old_config.option<ConfigOptionFloat>(opt_key);
+                    const auto *new_gap_fill_speed = new_config.option<ConfigOptionFloat>(opt_key);
+                    assert(old_gap_fill_speed && new_gap_fill_speed);
+                    return (old_gap_fill_speed->value > 0.f && new_gap_fill_speed->value == 0.f) ||
+                           (old_gap_fill_speed->value == 0.f && new_gap_fill_speed->value > 0.f);
+                }
+                return false;
+            };
+
+            // Filtering of unprintable regions in multi-material segmentation depends on if gap-fill is enabled or not.
+            // So step posSlice is invalidated when gap-fill was enabled/disabled by option "gap_fill_enabled" or by
+            // changing "gap_fill_speed" to force recomputation of the multi-material segmentation.
+            if (this->is_mm_painted() && (opt_key == "gap_fill_enabled" || (opt_key == "gap_fill_speed" && is_gap_fill_changed_state_due_to_speed())))
+                steps.emplace_back(posSlice);
+            steps.emplace_back(posPerimeters);
         } else if (
                opt_key == "layer_height"
             || opt_key == "first_layer_height"