_single_exposure is now a member variable for each GtkCanvas.

Gtk coalesces multiple exposes into a single combined rect.
If _single_exposure is disabled, we break apart the individual expose rects for the canvas rendering.

libs/canvas/canvas.cc

@@ -382,6 +382,7 @@ GtkCanvas::GtkCanvas ()
 	, _new_current_item (0)
 	, _grabbed_item (0)
 	, _focused_item (0)
+	, _single_exposure (1)
 	, current_tooltip_item (0)
 	, tooltip_window (0)
 {
@@ -786,11 +787,11 @@ GtkCanvas::on_expose_event (GdkEventExpose* ev)
         draw_context->fill ();
         
         /* render canvas */
+		if ( _single_exposure ) {
 	
-#define CANVAS_SINGLE_EXPOSE
-#ifdef CANVAS_SINGLE_EXPOSE
 			render (Rect (ev->area.x, ev->area.y, ev->area.x + ev->area.width, ev->area.y + ev->area.height), draw_context);
-#else
+
+		} else {
 			GdkRectangle* rects;
 			gint nrects;
 			
@@ -800,7 +801,7 @@ GtkCanvas::on_expose_event (GdkEventExpose* ev)
 				render (Rect (rects[n].x, rects[n].y, rects[n].x + rects[n].width, rects[n].y + rects[n].height), draw_context);
 			}
 			g_free (rects);
-#endif	
+		}
 		
 #ifdef USE_CAIRO_IMAGE_SURFACE
 	/* now blit our private surface back to the GDK one */

libs/canvas/canvas/canvas.h

@@ -226,6 +226,8 @@ private:
         /** the item that currently has key focus or 0 */
 	Item * _focused_item;
 	
+	bool _single_exposure;
+
 	sigc::connection tooltip_timeout_connection;
 	Item* current_tooltip_item;
 	Gtk::Window* tooltip_window;