Keeps objects on bed while scaling them using the scale gizmo

src/libslic3r/Technologies.hpp

@@ -23,6 +23,8 @@
 #define ENABLE_MODIFIED_CAMERA_TARGET (1 && ENABLE_1_42_0)
 // Add Geometry::Transformation class and use it into ModelInstance, ModelVolume and GLVolume
 #define ENABLE_MODELVOLUME_TRANSFORM (1 && ENABLE_1_42_0)
+// Keeps objects on bed while scaling them using the scale gizmo
+#define ENABLE_ENSURE_ON_BED_WHILE_SCALING (1 && ENABLE_MODELVOLUME_TRANSFORM)
 // Gizmos always rendered on top of objects
 #define ENABLE_GIZMOS_ON_TOP (1 && ENABLE_1_42_0)
 // New menu layout (open/save/save as project + import/export)

src/slic3r/GUI/GLCanvas3D.cpp

@@ -1639,6 +1639,10 @@ void GLCanvas3D::Selection::scale(const Vec3d& scale)
         _synchronize_unselected_volumes();
 #endif // !DISABLE_INSTANCES_SYNCH
 
+#if ENABLE_ENSURE_ON_BED_WHILE_SCALING
+    _ensure_on_bed();
+#endif // ENABLE_ENSURE_ON_BED_WHILE_SCALING
+
     m_bounding_box_dirty = true;
 }
 
@@ -2302,6 +2306,19 @@ void GLCanvas3D::Selection::_synchronize_unselected_volumes()
     }
 }
 
+#if ENABLE_ENSURE_ON_BED_WHILE_SCALING
+void GLCanvas3D::Selection::_ensure_on_bed()
+{
+    for (unsigned int i : m_list)
+    {
+        GLVolume* volume = (*m_volumes)[i];
+        double min_z = volume->transformed_convex_hull_bounding_box().min(2);
+        if (min_z != 0.0)
+            volume->set_instance_offset(Z, volume->get_instance_offset(Z) - min_z);
+    }
+}
+#endif // ENABLE_ENSURE_ON_BED_WHILE_SCALING
+
 const float GLCanvas3D::Gizmos::OverlayTexturesScale = 0.75f;
 const float GLCanvas3D::Gizmos::OverlayOffsetX = 10.0f * OverlayTexturesScale;
 const float GLCanvas3D::Gizmos::OverlayGapY = 5.0f * OverlayTexturesScale;

src/slic3r/GUI/GLCanvas3D.hpp

@@ -559,6 +559,9 @@ public:
         void _render_bounding_box(const BoundingBoxf3& box, float* color) const;
         void _synchronize_unselected_instances();
         void _synchronize_unselected_volumes();
+#if ENABLE_ENSURE_ON_BED_WHILE_SCALING
+        void _ensure_on_bed();
+#endif // ENABLE_ENSURE_ON_BED_WHILE_SCALING
     };
 
 private: