Scale to Fit Print Volume: fit the area every nozzle reaches

Each nozzle reaches only part of the bed on a multi-nozzle printer (H2D:
left 0-325, right 25-350 in X), but the command fitted the whole 350 mm
bed. A model that filled the bed in X therefore landed outside both
nozzles' printable range, and right after the user asked to fit it the
plater warned "The position or size of the model exceeds the right
nozzle's printable range".

Fit the volume every nozzle shares instead -- the same region Arrange
already places items in -- and centre on it rather than on the bed.

src/slic3r/GUI/Plater.cpp

@@ -11040,7 +11040,11 @@ void Plater::priv::scale_selection_to_fit_print_volume()
     PartPlate*    plate      = this->partplate_list.get_curr_plate();
     const Vec3d   bed_center = plate != nullptr ? plate->get_center_origin() :
                                                   Vec3d(volume.bed_center().x(), volume.bed_center().y(), 0.);
-    this->view3D->get_canvas3d()->get_selection().scale_to_fit_print_volume(volume, Vec2d(bed_center.x(), bed_center.y()));
+    // On a multi-nozzle printer each nozzle reaches only part of the bed, so a model fitted
+    // to the bed can still exceed a nozzle's printable range. Fit into the volume every
+    // nozzle shares, which is also the area Arrange places items in.
+    const BoundingBoxf3 print_volume = plate != nullptr ? plate->get_build_volume(true) : volume.bounding_volume();
+    this->view3D->get_canvas3d()->get_selection().scale_to_fit_print_volume(volume, Vec2d(bed_center.x(), bed_center.y()), print_volume);
 #else
     this->view3D->get_canvas3d()->get_selection().scale_to_fit_print_volume(*config);
 #endif // ENABLE_ENHANCED_PRINT_VOLUME_FIT

src/slic3r/GUI/Selection.cpp

@@ -1495,7 +1495,7 @@ void Selection::scale(const Vec3d& scale, TransformationType transformation_type
 }
 
 #if ENABLE_ENHANCED_PRINT_VOLUME_FIT
-void Selection::scale_to_fit_print_volume(const BuildVolume& volume, const Vec2d& bed_center)
+void Selection::scale_to_fit_print_volume(const BuildVolume& volume, const Vec2d& bed_center, const BoundingBoxf3& print_volume)
 {
     auto fit = [this](double s, Vec3d offset) {
         if (s <= 0.0 || s == 1.0)
@@ -1525,8 +1525,7 @@ void Selection::scale_to_fit_print_volume(const BuildVolume& volume, const Vec2d
         //wxGetApp().obj_manipul()->set_dirty();
     };
 
-    auto fit_rectangle = [this, fit, &bed_center](const BuildVolume& volume) {
-        const BoundingBoxf3 print_volume = volume.bounding_volume();
+    auto fit_rectangle = [this, fit, &print_volume]() {
         const Vec3d print_volume_size = print_volume.size();
 
         // adds 1/100th of a mm on all sides to avoid false out of print volume detections due to floating-point roundings
@@ -1537,7 +1536,7 @@ void Selection::scale_to_fit_print_volume(const BuildVolume& volume, const Vec2d
         const double sz = (box_size.z() != 0.0) ? print_volume_size.z() / box_size.z() : 0.0;
 
         if (sx != 0.0 && sy != 0.0 && sz != 0.0)
-            fit(std::min(sx, std::min(sy, sz)), Vec3d(bed_center.x(), bed_center.y(), print_volume.center().z()) - get_bounding_box().center());
+            fit(std::min(sx, std::min(sy, sz)), print_volume.center() - get_bounding_box().center());
     };
 
     auto fit_circle = [this, fit, &bed_center](const BuildVolume& volume) {
@@ -1582,7 +1581,7 @@ void Selection::scale_to_fit_print_volume(const BuildVolume& volume, const Vec2d
 
     switch (volume.type())
     {
-    case BuildVolume_Type::Rectangle: { fit_rectangle(volume); break; }
+    case BuildVolume_Type::Rectangle: { fit_rectangle(); break; }
     case BuildVolume_Type::Circle:    { fit_circle(volume); break; }
     default: { break; }
     }

src/slic3r/GUI/Selection.hpp

@@ -355,8 +355,9 @@ public:
     void scale(const Vec3d& scale, TransformationType transformation_type);
 #if ENABLE_ENHANCED_PRINT_VOLUME_FIT
     // bed_center is the centre of the plate the selection is on: every plate shares the
-    // bed size, but each sits at its own origin.
-    void scale_to_fit_print_volume(const BuildVolume& volume, const Vec2d& bed_center);
+    // bed size, but each sits at its own origin. print_volume is the box the selection must
+    // fit in, which is the area every nozzle reaches rather than the whole bed.
+    void scale_to_fit_print_volume(const BuildVolume& volume, const Vec2d& bed_center, const BoundingBoxf3& print_volume);
 #else
     void scale_to_fit_print_volume(const DynamicPrintConfig& config);
 #endif // ENABLE_ENHANCED_PRINT_VOLUME_FIT