From 368cfedbc72ac2da35ef0cc60ae176f676784e47 Mon Sep 17 00:00:00 2001
From: enricoturri1966 <enricoturri@seznam.cz>
Date: Tue, 20 Jul 2021 15:32:24 +0200
Subject: [PATCH] Keep non-sinking volumes on top of the printbed while scaling

---
 src/slic3r/GUI/Selection.cpp | 33 ++++++++++++++++++++++++++-------
 src/slic3r/GUI/Selection.hpp |  4 ++++
 2 files changed, 30 insertions(+), 7 deletions(-)

diff --git a/src/slic3r/GUI/Selection.cpp b/src/slic3r/GUI/Selection.cpp
index c38b88c3e..f2e879605 100644
--- a/src/slic3r/GUI/Selection.cpp
+++ b/src/slic3r/GUI/Selection.cpp
@@ -838,8 +838,21 @@ void Selection::scale(const Vec3d& scale, TransformationType transformation_type
     if (!m_valid)
         return;
 
+#if ENABLE_ALLOW_NEGATIVE_Z
+    bool is_any_volume_sinking = false;
+#if DISABLE_ALLOW_NEGATIVE_Z_FOR_SLA
+    bool is_sla = wxGetApp().preset_bundle->printers.get_edited_preset().printer_technology() == ptSLA;
+#endif // DISABLE_ALLOW_NEGATIVE_Z_FOR_SLA
+#endif // ENABLE_ALLOW_NEGATIVE_Z
+
     for (unsigned int i : m_list) {
         GLVolume &volume = *(*m_volumes)[i];
+#if ENABLE_ALLOW_NEGATIVE_Z
+#if DISABLE_ALLOW_NEGATIVE_Z_FOR_SLA
+        if (!is_sla)
+#endif // DISABLE_ALLOW_NEGATIVE_Z_FOR_SLA
+            is_any_volume_sinking |= !volume.is_modifier && std::find(m_cache.sinking_volumes.begin(), m_cache.sinking_volumes.end(), i) != m_cache.sinking_volumes.end();
+#endif // ENABLE_ALLOW_NEGATIVE_Z
         if (is_single_full_instance()) {
             if (transformation_type.relative()) {
                 Transform3d m = Geometry::assemble_transform(Vec3d::Zero(), Vec3d::Zero(), scale);
@@ -895,10 +908,10 @@ void Selection::scale(const Vec3d& scale, TransformationType transformation_type
         synchronize_unselected_volumes();
 #endif // !DISABLE_INSTANCES_SYNCH
     
-#if DISABLE_ALLOW_NEGATIVE_Z_FOR_SLA
-    if (wxGetApp().preset_bundle->printers.get_edited_preset().printer_technology() == ptSLA)
+#if ENABLE_ALLOW_NEGATIVE_Z
+    if (!is_any_volume_sinking)
         ensure_on_bed();
-#endif // DISABLE_ALLOW_NEGATIVE_Z_FOR_SLA
+#endif // ENABLE_ALLOW_NEGATIVE_Z
 
     this->set_bounding_boxes_dirty();
 }
@@ -1644,10 +1657,16 @@ void Selection::update_type()
 void Selection::set_caches()
 {
     m_cache.volumes_data.clear();
-    for (unsigned int i = 0; i < (unsigned int)m_volumes->size(); ++i)
-    {
-        const GLVolume* v = (*m_volumes)[i];
-        m_cache.volumes_data.emplace(i, VolumeCache(v->get_volume_transformation(), v->get_instance_transformation()));
+#if ENABLE_ALLOW_NEGATIVE_Z
+    m_cache.sinking_volumes.clear();
+#endif // ENABLE_ALLOW_NEGATIVE_Z
+    for (unsigned int i = 0; i < (unsigned int)m_volumes->size(); ++i) {
+        const GLVolume& v = *(*m_volumes)[i];
+        m_cache.volumes_data.emplace(i, VolumeCache(v.get_volume_transformation(), v.get_instance_transformation()));
+#if ENABLE_ALLOW_NEGATIVE_Z
+        if (v.is_sinking())
+            m_cache.sinking_volumes.push_back(i);
+#endif // ENABLE_ALLOW_NEGATIVE_Z
     }
     m_cache.dragging_center = get_bounding_box().center();
 }
diff --git a/src/slic3r/GUI/Selection.hpp b/src/slic3r/GUI/Selection.hpp
index ae82f9ca7..c6409f9f2 100644
--- a/src/slic3r/GUI/Selection.hpp
+++ b/src/slic3r/GUI/Selection.hpp
@@ -186,6 +186,10 @@ private:
         // to a set of indices of ModelVolume instances in ModelObject::instances
         // Here the index means a position inside the respective std::vector, not ObjectID.
         ObjectIdxsToInstanceIdxsMap content;
+#if ENABLE_ALLOW_NEGATIVE_Z
+        // List of ids of the volumes which are sinking when starting dragging
+        std::vector<unsigned int> sinking_volumes;
+#endif // ENABLE_ALLOW_NEGATIVE_Z
     };
 
     // Volumes owned by GLCanvas3D.