ModelExporters are allowed to maintain a state

Add virtual clone() method to work around the troubles

include/imodel.h

@@ -112,6 +112,9 @@ class ModelNode
 };
 typedef std::shared_ptr<ModelNode> ModelNodePtr;
 
+class IModelExporter;
+typedef std::shared_ptr<IModelExporter> IModelExporterPtr;
+
 /**
 * Exporter Interface for models (meshes).
 */
@@ -121,6 +124,11 @@ class IModelExporter
 	virtual ~IModelExporter()
 	{}
 
+	// Virtual constructor idiom. Use this method to generate a new
+	// instance of the implementing subclass. This way the model format manager
+	// can create a fresh instance of this exporter on demand.
+	virtual IModelExporterPtr clone() = 0;
+
 	// Returns the uppercase file extension this exporter is suitable for
 	virtual const std::string& getExtension() const = 0;
 
@@ -130,11 +138,13 @@ class IModelExporter
 	// Export the model file to the given stream
 	virtual void exportToStream(std::ostream& stream) = 0;
 };
-typedef std::shared_ptr<IModelExporter> IModelExporterPtr;
 
 /**
  * Importer interface for models. An importer must be able
  * to load a model (node) from the VFS.
+ * The importer instance shouldn't maintain an internal state,
+ * such that the same instance can be used to load several models,
+ * from different client code.
  */
 class IModelImporter
 {

plugins/model/AseExporter.cpp

@@ -12,6 +12,11 @@ namespace model
 AseExporter::AseExporter()
 {}
 
+IModelExporterPtr AseExporter::clone()
+{
+	return std::make_shared<AseExporter>();
+}
+
 const std::string& AseExporter::getExtension() const
 {
 	static std::string _extension("ASE");

plugins/model/AseExporter.h

@@ -39,6 +39,8 @@ class AseExporter :
 public:
 	AseExporter();
 
+	IModelExporterPtr clone() override;
+
 	// Returns the uppercase file extension this exporter is suitable for
 	const std::string& getExtension() const override;
 

plugins/model/Makefile.am

@@ -8,7 +8,8 @@ model_la_LDFLAGS = -module -avoid-version \
 model_la_LIBADD = $(top_builddir)/libs/picomodel/libpicomodel.la \
 				  $(top_builddir)/libs/math/libmath.la \
 				  $(top_builddir)/libs/scene/libscenegraph.la
-model_la_SOURCES = PicoModelNode.cpp \
+model_la_SOURCES = AseExporter.cpp \
+                   PicoModelNode.cpp \
                    RenderablePicoModel.cpp \
                    PicoModelLoader.cpp \
                    RenderablePicoSurface.cpp \

radiant/model/ModelFormatManager.cpp

@@ -102,7 +102,8 @@ IModelExporterPtr ModelFormatManager::getExporter(const std::string& extension)
 
 	ExporterMap::const_iterator found = _exporters.find(extensionUpper);
 
-	return found != _exporters.end() ? found->second : IModelExporterPtr();
+	// Return a cloned instance if we found a matching exporter
+	return found != _exporters.end() ? found->second->clone() : IModelExporterPtr();
 }
 
 module::StaticModule<ModelFormatManager> _staticModelFormatManagerModule;