From 25f4f1fe554bb6bc4bad44e768882446a58281c9 Mon Sep 17 00:00:00 2001
From: Vojtech Kral <vojtech@kral.hk>
Date: Mon, 26 Nov 2018 12:08:10 +0100
Subject: [PATCH] Cut: Use world coordinates

---
 src/libslic3r/Model.cpp    | 15 +++++++--------
 src/libslic3r/Model.hpp    |  2 +-
 src/slic3r/GUI/GLGizmo.cpp | 10 +++++-----
 3 files changed, 13 insertions(+), 14 deletions(-)

diff --git a/src/libslic3r/Model.cpp b/src/libslic3r/Model.cpp
index 871ac9497..a4c674bc0 100644
--- a/src/libslic3r/Model.cpp
+++ b/src/libslic3r/Model.cpp
@@ -1005,15 +1005,10 @@ ModelObjectPtrs ModelObject::cut(size_t instance, coordf_t z, bool keep_upper, b
 
     // Because transformations are going to be applied to meshes directly,
     // we reset transformation of all instances and volumes,
-    // _except_ for translation, which is preserved in the transformation matrix
+    // except for translation, which is preserved in the transformation matrix
     // and not applied to the mesh transform.
     // TODO: Do the same for Z-rotation as well?
 
-    // Convert z from relative to bb's base to object coordinates
-    // FIXME: doesn't work well for rotated objects
-    const auto bb = instance_bounding_box(instance, true);
-    z -= bb.min(2);
-
     if (keep_upper) {
         for (auto *instance : upper->instances) { cut_reset_transform(instance); }
     }
@@ -1030,11 +1025,15 @@ ModelObjectPtrs ModelObject::cut(size_t instance, coordf_t z, bool keep_upper, b
             TriangleMesh upper_mesh, lower_mesh;
 
             // Transform the mesh by the object transformation matrix
-            volume->mesh.transform(instance_matrix * volume->get_matrix(true));
+            const auto volume_tr = instance_matrix * volume->get_matrix(true);
+            volume->mesh.transform(volume_tr);
             cut_reset_transform(volume);
 
+            // Transform z from world to object
+            const auto local_z = volume_tr * Vec3d(0.0, 0.0, z);
+
             TriangleMeshSlicer tms(&volume->mesh);
-            tms.cut(z, &upper_mesh, &lower_mesh);
+            tms.cut(local_z(2), &upper_mesh, &lower_mesh);
 
             if (keep_upper) {
                 upper_mesh.repair();
diff --git a/src/libslic3r/Model.hpp b/src/libslic3r/Model.hpp
index 8b8a0f59b..b9831336c 100644
--- a/src/libslic3r/Model.hpp
+++ b/src/libslic3r/Model.hpp
@@ -238,7 +238,7 @@ public:
     size_t materials_count() const;
     size_t facets_count() const;
     bool needed_repair() const;
-    ModelObjectPtrs cut(size_t instance, coordf_t z, bool keep_upper = true, bool keep_lower = true, bool rotate_lower = false);
+    ModelObjectPtrs cut(size_t instance, coordf_t z, bool keep_upper = true, bool keep_lower = true, bool rotate_lower = false);    // Note: z is in world coordinates
     void split(ModelObjectPtrs* new_objects);
     void repair();
 
diff --git a/src/slic3r/GUI/GLGizmo.cpp b/src/slic3r/GUI/GLGizmo.cpp
index ed2a6f2d2..e2d57c8ab 100644
--- a/src/slic3r/GUI/GLGizmo.cpp
+++ b/src/slic3r/GUI/GLGizmo.cpp
@@ -1992,7 +1992,7 @@ void GLGizmoCut::on_set_state()
 {
     // Reset m_cut_z on gizmo activation
     if (get_state() == On) {
-        m_cut_z = 0.0;
+        m_cut_z = m_parent.get_selection().get_bounding_box().size()(2) / 2.0;
     }
 
 #ifndef ENABLE_IMGUI
@@ -2014,10 +2014,10 @@ void GLGizmoCut::on_start_dragging(const GLCanvas3D::Selection& selection)
 
     const BoundingBoxf3& box = selection.get_bounding_box();
     m_start_z = m_cut_z;
-    m_max_z = box.size()(2) / 2.0;
+    m_max_z = box.size()(2);
     m_drag_pos = m_grabbers[m_hover_id].center;
     m_drag_center = box.center();
-    m_drag_center(2) += m_cut_z;
+    m_drag_center(2) = m_cut_z;
 }
 
 void GLGizmoCut::on_update(const UpdateData& data)
@@ -2025,7 +2025,7 @@ void GLGizmoCut::on_update(const UpdateData& data)
     if (m_hover_id != -1) {
         // Clamp the plane to the object's bounding box
         const double new_z = m_start_z + calc_projection(data.mouse_ray);
-        m_cut_z = std::max(-m_max_z, std::min(m_max_z, new_z));
+        m_cut_z = std::max(0.0, std::min(m_max_z, new_z));
     }
 }
 
@@ -2037,7 +2037,7 @@ void GLGizmoCut::on_render(const GLCanvas3D::Selection& selection) const
 
     const BoundingBoxf3& box = selection.get_bounding_box();
     Vec3d plane_center = box.center();
-    plane_center(2) += m_cut_z;
+    plane_center(2) = m_cut_z;
 
     const float min_x = box.min(0) - Margin;
     const float max_x = box.max(0) + Margin;