Configurable overhang threshold as function of perimeter width (#3752)

* Fix automatic overhang threshold

We should be supporting perimeters that are overhung further than half a
perimeter out, rather than two times the perimeter width.

Fixes: #2068

* Made the overhang detection configurable, up to 200 (the original value, which is still the default)

* Set default to 60% as per https://github.com/alexrj/Slic3r/wiki/Support:-Requirements
Removed some less useful enumerations (0-30%)

* Folded in auto_threshold into support threshold as a % value

lib/Slic3r/GUI/Tab.pm

@@ -868,6 +868,7 @@ sub _update {
             support_material_spacing support_material_angle
             support_material_interface_layers dont_support_bridges
             support_material_extrusion_width support_material_contact_distance);
+
     $self->get_field($_)->toggle($have_support_material && $have_support_interface)
         for qw(support_material_interface_spacing support_material_interface_extruder
             support_material_interface_speed);

lib/Slic3r/Print/SupportMaterial.pm

@@ -92,7 +92,7 @@ sub contact_area {
     
     # if user specified a custom angle threshold, convert it to radians
     my $threshold_rad;
-    if ($self->object_config->support_material_threshold) {
+    if (!$self->object_config->support_material_threshold =~ /%$/) {
         $threshold_rad = deg2rad($self->object_config->support_material_threshold + 1);  # +1 makes the threshold inclusive
         Slic3r::debugf "Threshold angle = %d°\n", rad2deg($threshold_rad);
     }
@@ -152,7 +152,7 @@ sub contact_area {
                 } else {
                     $diff = diff(
                         [ map $_->p, @{$layerm->slices} ],
-                        offset([ map @$_, @{$lower_layer->slices} ], +$fw*2),
+                        offset([ map @$_, @{$lower_layer->slices} ], +$self->object_config->get_abs_value_over('support_material_threshold', $fw)),
                     );
                 
                     # collapse very tiny spots

xs/src/libslic3r/PrintConfig.cpp

@@ -1291,6 +1291,9 @@ PrintConfigDef::PrintConfigDef()
     def->min = 0;
     def->default_value = new ConfigOptionFloat(2.5);
 
+
+
+
     def = this->add("support_material_speed", coFloat);
     def->label = "Support material";
     def->gui_type = "f_enum_open";
@@ -1303,15 +1306,15 @@ PrintConfigDef::PrintConfigDef()
     def->enum_labels.push_back("auto");
     def->default_value = new ConfigOptionFloat(60);
 
-    def = this->add("support_material_threshold", coInt);
+    def = this->add("support_material_threshold", coFloatOrPercent);
     def->label = "Overhang threshold";
     def->category = "Support material";
-    def->tooltip = "Support material will not be generated for overhangs whose slope angle (90° = vertical) is above the given threshold. In other words, this value represent the most horizontal slope (measured from the horizontal plane) that you can print without support material. Set to zero for automatic detection (recommended).";
-    def->sidetext = "°";
-    def->cli = "support-material-threshold=i";
+    def->tooltip = "Support material will not be generated for overhangs whose slope angle (90° = vertical) is above the given threshold. In other words, this value represent the most horizontal slope (measured from the horizontal plane) that you can print without support material. Set to a percentage to automatically detect based on some % of overhanging perimeter width instead (recommended).";
+    def->sidetext = "° (or %)";
+    def->cli = "support-material-threshold=s";
     def->min = 0;
-    def->max = 90;
-    def->default_value = new ConfigOptionInt(0);
+    def->max = 300;
+    def->default_value = new ConfigOptionFloatOrPercent(60, true);
 
     def = this->add("temperature", coInts);
     def->label = "Other layers";

xs/src/libslic3r/PrintConfig.hpp

@@ -161,7 +161,7 @@ class PrintObjectConfig : public virtual StaticPrintConfig
     ConfigOptionEnum<SupportMaterialPattern> support_material_pattern;
     ConfigOptionFloat               support_material_spacing;
     ConfigOptionFloat               support_material_speed;
-    ConfigOptionInt                 support_material_threshold;
+    ConfigOptionFloatOrPercent      support_material_threshold;
     ConfigOptionFloat               xy_size_compensation;
     
     PrintObjectConfig(bool initialize = true) : StaticPrintConfig() {