Organic supports: Fixing crashes with invalid tip diameter or branch

diameter. Fixes SPE-1451 GH#9555

Fixed by reporting invalid combination of support extrusion width
and tip + branch diameter:

Organic support tree tip diameter must not be smaller than support material extrusion width.
Organic support branch diameter must not be smaller than 2x support material extrusion width.
Organic support branch diameter must not be smaller than support tree tip diameter.

src/libslic3r/Print.cpp

@@ -689,7 +689,7 @@ std::string Print::validate(std::vector<std::string>* warnings) const
 //        	double extrusion_width_min = config.get_abs_value(opt_key, min_nozzle_diameter);
 //        	double extrusion_width_max = config.get_abs_value(opt_key, max_nozzle_diameter);
             double extrusion_width_min = config.get_abs_value(opt_key, layer_height);
-            double extrusion_width_max = config.get_abs_value(opt_key, layer_height);
+            double extrusion_width_max = extrusion_width_min;
         	if (extrusion_width_min == 0) {
         		// Default "auto-generated" extrusion width is always valid.
         	} else if (extrusion_width_min <= layer_height) {
@@ -723,6 +723,17 @@ std::string Print::validate(std::vector<std::string>* warnings) const
     							     "(both support_material_extruder and support_material_interface_extruder need to be set to 0).");
     				}
                 }
+                if (object->config().support_material_style == smsOrganic) {
+                    float extrusion_width = std::min(
+                        support_material_flow(object).width(),
+                        support_material_interface_flow(object).width());
+                    if (object->config().support_tree_tip_diameter < extrusion_width - EPSILON)
+                        return _u8L("Organic support tree tip diameter must not be smaller than support material extrusion width.");
+                    if (object->config().support_tree_branch_diameter < 2. * extrusion_width - EPSILON)
+                        return _u8L("Organic support branch diameter must not be smaller than 2x support material extrusion width.");
+                    if (object->config().support_tree_branch_diameter < object->config().support_tree_tip_diameter)
+                        return _u8L("Organic support branch diameter must not be smaller than support tree tip diameter.");
+                }
             }
 
             // Do we have custom support data that would not be used?

src/libslic3r/Support/TreeSupportCommon.cpp

@@ -89,7 +89,8 @@ TreeSupportSettings::TreeSupportSettings(const TreeSupportMeshGroupSettings &mes
       maximum_move_distance((mesh_group_settings.support_tree_angle < M_PI / 2.) ? (coord_t)(tan(mesh_group_settings.support_tree_angle) * layer_height) : std::numeric_limits<coord_t>::max()),
       maximum_move_distance_slow((mesh_group_settings.support_tree_angle_slow < M_PI / 2.) ? (coord_t)(tan(mesh_group_settings.support_tree_angle_slow) * layer_height) : std::numeric_limits<coord_t>::max()),
       support_bottom_layers(mesh_group_settings.support_bottom_enable ? (mesh_group_settings.support_bottom_height + layer_height / 2) / layer_height : 0),
-      tip_layers(std::max((branch_radius - min_radius) / (support_line_width / 3), branch_radius / layer_height)), // Ensure lines always stack nicely even if layer height is large
+      // Ensure lines always stack nicely even if layer height is large.
+      tip_layers(std::max((branch_radius - min_radius) / (support_line_width / 3), branch_radius / layer_height)),
       branch_radius_increase_per_layer(tan(mesh_group_settings.support_tree_branch_diameter_angle) * layer_height),
       max_to_model_radius_increase(mesh_group_settings.support_tree_max_diameter_increase_by_merges_when_support_to_model / 2),
       min_dtt_to_model(round_up_divide(mesh_group_settings.support_tree_min_height_to_model, layer_height)),
@@ -116,6 +117,9 @@ TreeSupportSettings::TreeSupportSettings(const TreeSupportMeshGroupSettings &mes
       settings(mesh_group_settings),
       min_feature_size(mesh_group_settings.min_feature_size)
 {
+    // At least one tip layer must be defined.
+    assert(tip_layers > 0);
+
     layer_start_bp_radius = (bp_radius - branch_radius) / bp_radius_increase_per_layer;
 
     if (TreeSupportSettings::soluble) {