diff --git a/include/gds-render/output-renderers/external-renderer.h b/include/gds-render/output-renderers/external-renderer.h
index 2ded59c..7847f2c 100644
--- a/include/gds-render/output-renderers/external-renderer.h
+++ b/include/gds-render/output-renderers/external-renderer.h
@@ -24,35 +24,46 @@
  */
 
 /**
- * @addtogroup external-renderer
+ * @addtogroup ExternalRenderer
  * @{
  */
 
 #ifndef _EXTERNAL_RENDERER_H_
 #define _EXTERNAL_RENDERER_H_
 
+#include <gds-render/output-renderers/gds-output-renderer.h>
 #include <gds-render/gds-utils/gds-types.h>
-#include <glib.h>
+
+G_BEGIN_DECLS
+
+#define GDS_RENDER_TYPE_EXTERNAL_RENDERER (external_renderer_get_type())
+
+G_DECLARE_FINAL_TYPE(ExternalRenderer, external_renderer, GDS_RENDER, EXTERNAL_RENDERER, GdsOutputRenderer)
 
 /**
  * @brief function name expected to be found in external library.
  * 
  * The function has to be defined as follows:
  * @code
- * int function_name(gds_cell *toplevel, GList *layer_info_list, char *output_file_name)
+ * int EXTERNAL_LIBRARY_FUNCTION(gds_cell *toplevel, GList *layer_info_list, const char *output_file_name, double scale)
  * @endcode
  */
 #define EXTERNAL_LIBRARY_FUNCTION "render_cell_to_file"
 
 /**
- * @brief external_renderer_render_cell
- * @param toplevel_cell The toplevel cell to render
- * @param layer_info_list The layer information. Contains #layer_info elements
- * @param output_file Output file
- * @param so_path Path to the shared object file containing #EXTERNAL_LIBRARY_FUNCTION
- * @return 0 on success
+ * @brief Create new ExternalRenderer object
+ * @return New object
  */
-int external_renderer_render_cell(struct gds_cell *toplevel_cell, GList *layer_info_list, char *output_file, char *so_path);
+ExternalRenderer *external_renderer_new();
+
+/**
+ * @brief Create new ExternalRenderer object with specified shared object path
+ * @param so_path Path to shared object, the rendering function is searched in
+ * @return New object.
+ */
+ExternalRenderer *external_renderer_new_with_so(const char *so_path);
+
+G_END_DECLS
 
 #endif /* _EXTERNAL_RENDERER_H_ */
 
diff --git a/output-renderers/external-renderer.c b/output-renderers/external-renderer.c
index 66d7f78..4af96aa 100644
--- a/output-renderers/external-renderer.c
+++ b/output-renderers/external-renderer.c
@@ -24,7 +24,7 @@
  */
 
 /**
- * @addtogroup external-renderer
+ * @addtogroup ExternalRenderer
  * @{
  */
 
@@ -33,10 +33,25 @@
 
 #include <gds-render/output-renderers/external-renderer.h>
 
-int external_renderer_render_cell(struct gds_cell *toplevel_cell, GList *layer_info_list,
-				  char *output_file, char *so_path)
+struct _ExternalRenderer {
+	GdsOutputRenderer parent;
+	const char *shared_object_path;
+};
+
+G_DEFINE_TYPE(ExternalRenderer, external_renderer, GDS_RENDER_TYPE_OUTPUT_RENDERER)
+
+/**
+ * @brief Execute render function in shared object to render the supplied cell
+ * @param toplevel_cell Cell to render
+ * @param layer_info_list Layer information (Color etc.)
+ * @param output_file Destination file
+ * @param so_path Path to shared object
+ * @return 0 if successful
+ */
+static int external_renderer_render_cell(struct gds_cell *toplevel_cell, GList *layer_info_list,
+				   const char *output_file, double scale,  const char *so_path)
 {
-	int (*so_render_func)(struct gds_cell *, GList *, char *) = NULL;
+	int (*so_render_func)(struct gds_cell *, GList *, const char *, double) = NULL;
 	void *so_handle = NULL;
 	char *error_msg;
 	int ret = 0;
@@ -48,25 +63,53 @@ int external_renderer_render_cell(struct gds_cell *toplevel_cell, GList *layer_i
 	/* Load shared object */
 	so_handle = dlopen(so_path, RTLD_LAZY);
 	if (!so_handle) {
-		printf("Could not load external library '%s'\nDetailed error is:\n%s\n", so_path, dlerror());
+		g_error("Could not load external library '%s'\nDetailed error is:\n%s", so_path, dlerror());
 		return -2000;
 	}
 
 	/* Load symbol from library */
-	so_render_func = (int (*)(struct gds_cell *, GList *, char *))dlsym(so_handle, EXTERNAL_LIBRARY_FUNCTION);
+	so_render_func = (int (*)(struct gds_cell *, GList *, const char *, double))dlsym(so_handle, EXTERNAL_LIBRARY_FUNCTION);
 	error_msg = dlerror();
 	if (error_msg != NULL) {
-		printf("Rendering function not found in library:\n%s\n", error_msg);
+		g_error("Rendering function not found in library:\n%s\n", error_msg);
 		goto ret_close_so_handle;
 	}
 
 	/* Execute */
 	if (so_render_func)
-		so_render_func(toplevel_cell, layer_info_list, output_file);
+		ret = so_render_func(toplevel_cell, layer_info_list, output_file, scale);
 
 ret_close_so_handle:
 	dlclose(so_handle);
 	return ret;
 }
 
+static int external_renderer_render_output(GdsOutputRenderer *renderer,
+					    struct gds_cell *cell,
+					    GList *layer_infos,
+					    const char *output_file,
+					    double scale)
+{
+	ExternalRenderer *ext_renderer = GDS_RENDER_EXTERNAL_RENDERER(renderer);
+
+	return external_renderer_render_cell(cell, layer_infos, output_file, scale, ext_renderer->shared_object_path);
+}
+
+static void external_renderer_class_init(ExternalRendererClass *klass)
+{
+	GdsOutputRendererClass *inherited_parent_class;
+
+	inherited_parent_class = GDS_RENDER_OUTPUT_RENDERER_CLASS(klass);
+
+	/* Override virtual function */
+	inherited_parent_class->render_output = external_renderer_render_output;
+}
+
+static void external_renderer_init(ExternalRenderer *self)
+{
+	self->shared_object_path = NULL;
+}
+
+
+
 /** @} */