Fix for empty zip when the object is moved after slicing

src/libslic3r/SLAPrint.cpp

@@ -567,19 +567,7 @@ void SLAPrint::process()
         }
     };
 
-    using Layer = sla::ExPolygons;
-    using LayerCopies = std::vector<SLAPrintObject::Instance>;
-    struct LayerRef {
-        std::reference_wrapper<const Layer> lref;
-        std::reference_wrapper<const LayerCopies> copies;
-        LayerRef(const Layer& lyr, const LayerCopies& cp) :
-            lref(std::cref(lyr)), copies(std::cref(cp)) {}
-    };
-
-    using LevelID = long long;
-    using LayerRefs = std::vector<LayerRef>;
-    // layers according to quantized height levels
-    std::map<LevelID, LayerRefs> levels;
+    auto& levels = m_printer_input;
 
     // We have the layer polygon collection but we need to unite them into
     // an index where the key is the height level in discrete levels (clipper)

src/libslic3r/SLAPrint.hpp

@@ -200,7 +200,31 @@ private:
 
     PrintObjects                    m_objects;
     std::vector<bool>               m_stepmask;
-    SLAPrinterPtr                   m_printer;
+
+    // Definition of the print input map. It consists of the slices indexed
+    // with scaled (clipper) Z coordinates. Also contains the instance
+    // transformations in scaled and filtered version. This is enough for the
+    // rasterizer to be able to draw every layer in the right position
+    using Layer = ExPolygons;
+    using LayerCopies = std::vector<SLAPrintObject::Instance>;
+    struct LayerRef {
+        std::reference_wrapper<const Layer> lref;
+        std::reference_wrapper<const LayerCopies> copies;
+        LayerRef(const Layer& lyr, const LayerCopies& cp) :
+            lref(std::cref(lyr)), copies(std::cref(cp)) {}
+    };
+
+    // Layers according to quantized height levels. This will be consumed by
+    // the printer (rasterizer) in the SLAPrint class.
+    using LevelID = long long;
+
+    // One level may contain multiple slices from multiple objects and their
+    // supports
+    using LayerRefs = std::vector<LayerRef>;
+    std::map<LevelID, LayerRefs>            m_printer_input;
+
+    // The printer itself
+    SLAPrinterPtr                           m_printer;
 
 	friend SLAPrintObject;
 };