Combine brims option (Prusa style brims) (#12343)

* Union ex brims

Revert "Union ex brims"

This reverts commit bbc9a39faf318dc2df093eb2bdcebf19a4162fe9.

Update Brim.cpp

* dont repeat paths

* Update Brim.cpp

* multimaterial brim independiente

* Normal brim if is by object

* fix print order

* cleaning 1

* cleaning 2

* Normal brim if multimaterial on first layer

* fix artifact

* combine_brim optional

refactoring

* refactoring gcode.cpp

* refactoring brim.cpp

Update Brim.cpp

* Remove multimaterial first-layer check for brims

Stop detecting extruders used on the first layer and remove the is_multimaterial_first_layer guard. Simplify can_combine_brims to only consider combine_brims and whether printing is ByObject, allowing brims to be combined across extruders unless printing by object or combine_brims is disabled. Cleans up unused code and simplifies brim-generation conditions.

* Remove material specification from unified brim comment

* Update PrintConfig.cpp

src/libslic3r/GCode.cpp

@@ -4993,6 +4993,39 @@ LayerResult GCode::process_layer(
     bool has_insert_wrapping_detection_gcode = false;
 
     // Extrude the skirt, brim, support, perimeters, infill ordered by the extruders.
+    // Orca: Print unified global brim before any object.
+    // Only do this if `combine_brims` is enabled and we are printing by layer.
+    if (first_layer && sequence_by_layer && m_config.combine_brims && !print.m_brimMap.empty()) {
+        const ObjectID unified_object_id = [&]() -> ObjectID {
+            ObjectID id;
+            bool     found = false;
+            for (const auto& [obj_id, brim] : print.m_brimMap) {
+                const bool has_printable_entities = std::any_of(brim.entities.begin(), brim.entities.end(),
+                                                                [](const ExtrusionEntity* ee) { return ee != nullptr; });
+                if (!has_printable_entities)
+                    continue;
+                if (found)
+                    return ObjectID();
+                id    = obj_id;
+                found = true;
+            }
+            return found ? id : ObjectID();
+        }();
+
+        if (unified_object_id.valid()) {
+            const auto it = print.m_brimMap.find(unified_object_id);
+            if (it != print.m_brimMap.end()) {
+                this->set_origin(0., 0.);
+                for (const ExtrusionEntity* ee : it->second.entities)
+                    if (ee != nullptr)
+                        gcode += this->extrude_entity(*ee, "brim", m_config.support_speed.value);
+
+                // Mark brim as printed for this object to avoid per-object brim emission later.
+                this->m_objsWithBrim.erase(unified_object_id);
+            }
+        }
+    }
+
     for (unsigned int extruder_id : layer_tools.extruders)
     {
         if (print.config().skirt_type == stCombined && !print.skirt().empty())