From 382326ffc85620edbe320e956439caccca9df271 Mon Sep 17 00:00:00 2001
From: bubnikv <bubnikv@gmail.com>
Date: Wed, 3 Apr 2019 11:12:03 +0200
Subject: [PATCH] Fixed FFF slicing of meshes with left hand oriented
 transformations applied. Slight optimization of FFF slicing - optimized copy
 of an object with just a single volume.

---
 src/libslic3r/PrintObject.cpp  | 17 +++++++++--------
 src/libslic3r/TriangleMesh.cpp |  7 ++++++-
 src/libslic3r/TriangleMesh.hpp |  2 +-
 3 files changed, 16 insertions(+), 10 deletions(-)

diff --git a/src/libslic3r/PrintObject.cpp b/src/libslic3r/PrintObject.cpp
index 6c04c7781..42c6fbf75 100644
--- a/src/libslic3r/PrintObject.cpp
+++ b/src/libslic3r/PrintObject.cpp
@@ -1790,15 +1790,16 @@ std::vector<ExPolygons> PrintObject::_slice_volumes(const std::vector<float> &z,
     if (! volumes.empty()) {
         // Compose mesh.
         //FIXME better to perform slicing over each volume separately and then to use a Boolean operation to merge them.
-        TriangleMesh mesh;
-        for (const ModelVolume *v : volumes)
-        {
-            TriangleMesh vol_mesh(v->mesh);
-            vol_mesh.transform(v->get_matrix());
+        TriangleMesh mesh(volumes.front()->mesh);
+        mesh.transform(volumes.front()->get_matrix(), true);
+        for (size_t idx_volume = 1; idx_volume < volumes.size(); ++ idx_volume) {
+            const ModelVolume &model_volume = *volumes[idx_volume];
+            TriangleMesh vol_mesh(model_volume.mesh);
+            vol_mesh.transform(model_volume.get_matrix(), true);
             mesh.merge(vol_mesh);
         }
         if (mesh.stl.stats.number_of_facets > 0) {
-            mesh.transform(m_trafo);
+            mesh.transform(m_trafo, true);
             // apply XY shift
             mesh.translate(- unscale<float>(m_copies_shift(0)), - unscale<float>(m_copies_shift(1)), 0);
             // perform actual slicing
@@ -1819,9 +1820,9 @@ std::vector<ExPolygons> PrintObject::_slice_volume(const std::vector<float> &z,
     // Compose mesh.
     //FIXME better to perform slicing over each volume separately and then to use a Boolean operation to merge them.
     TriangleMesh mesh(volume.mesh);
-    mesh.transform(volume.get_matrix());
+    mesh.transform(volume.get_matrix(), true);
     if (mesh.stl.stats.number_of_facets > 0) {
-        mesh.transform(m_trafo);
+        mesh.transform(m_trafo, true);
         // apply XY shift
         mesh.translate(- unscale<float>(m_copies_shift(0)), - unscale<float>(m_copies_shift(1)), 0);
         // perform actual slicing
diff --git a/src/libslic3r/TriangleMesh.cpp b/src/libslic3r/TriangleMesh.cpp
index c145380c9..0d9a79978 100644
--- a/src/libslic3r/TriangleMesh.cpp
+++ b/src/libslic3r/TriangleMesh.cpp
@@ -314,10 +314,15 @@ void TriangleMesh::mirror(const Axis &axis)
     stl_invalidate_shared_vertices(&this->stl);
 }
 
-void TriangleMesh::transform(const Transform3d& t)
+void TriangleMesh::transform(const Transform3d& t, bool fix_left_handed)
 {
     stl_transform(&stl, t);
     stl_invalidate_shared_vertices(&stl);
+	if (fix_left_handed && t.matrix().block(0, 0, 3, 3).determinant() < 0.) {
+		// Left handed transformation is being applied. It is a good idea to flip the faces and their normals.
+		this->repair();
+		stl_reverse_all_facets(&stl);
+	}
 }
 
 void TriangleMesh::align_to_origin()
diff --git a/src/libslic3r/TriangleMesh.hpp b/src/libslic3r/TriangleMesh.hpp
index a65a4be75..527846f9d 100644
--- a/src/libslic3r/TriangleMesh.hpp
+++ b/src/libslic3r/TriangleMesh.hpp
@@ -49,7 +49,7 @@ public:
     void mirror_x() { this->mirror(X); }
     void mirror_y() { this->mirror(Y); }
     void mirror_z() { this->mirror(Z); }
-    void transform(const Transform3d& t);
+    void transform(const Transform3d& t, bool fix_left_handed = false);
     void align_to_origin();
     void rotate(double angle, Point* center);
     TriangleMeshPtrs split() const;