allow to use cairo-image/software surface for canvas & cairowidgets

[ardour.git] / libs / canvas / canvas.cc

diff --git a/libs/canvas/canvas.cc b/libs/canvas/canvas.cc
index 133e09484c5522a701fad8dfd585ae773e1b4dd3..9d1d9f3ad9df7c5965b85c827ae4f6fdbe25b79d 100644 (file)
--- a/libs/canvas/canvas.cc
+++ b/libs/canvas/canvas.cc
@@ -720,6 +720,18 @@ GtkCanvas::item_going_away (Item* item, boost::optional<Rect> bounding_box)
        
 }
 
+void
+GtkCanvas::on_size_allocate (Gtk::Allocation& a)
+{
+       EventBox::on_size_allocate (a);
+#ifdef USE_CAIRO_IMAGE_SURFACE
+       /* allocate an image surface as large as the canvas itself */
+
+       canvas_image.clear ();
+       canvas_image = Cairo::ImageSurface::create (Cairo::FORMAT_ARGB32, a.get_width(), a.get_height());
+#endif
+}
+
 /** Handler for GDK expose events.
  *  @param ev Event.
  *  @return true if the event was handled.
@@ -727,21 +739,49 @@ GtkCanvas::item_going_away (Item* item, boost::optional<Rect> bounding_box)
 bool
 GtkCanvas::on_expose_event (GdkEventExpose* ev)
 {
+#ifdef USE_CAIRO_IMAGE_SURFACE
+       if (!canvas_image) {
+               canvas_image = Cairo::ImageSurface::create (Cairo::FORMAT_ARGB32, get_width(), get_height());
+       }
+
+       {
+               /* scope for image_context */
+               Cairo::RefPtr<Cairo::Context> image_context = Cairo::Context::create (canvas_image);
+
+               /* clear expose area to transparent */
+
+               image_context->save ();
+               image_context->rectangle (ev->area.x, ev->area.y, ev->area.width, ev->area.height);
+               image_context->clip ();
+               image_context->set_operator (Cairo::OPERATOR_CLEAR);
+               image_context->paint ();
+               image_context->restore ();
+
+               /* render into image surface */
+
+               render (Rect (ev->area.x, ev->area.y, ev->area.x + ev->area.width, ev->area.y + ev->area.height), image_context);
+
+               /* image surface is flushed when image_context goes out of scope */
+       }
+
+       /* now blit our private surface back to the GDK one */
+
+       Cairo::RefPtr<Cairo::Context> cairo_context = get_window()->create_cairo_context ();
+
+       cairo_context->rectangle (ev->area.x, ev->area.y, ev->area.width, ev->area.height);
+       cairo_context->clip ();
+       cairo_context->set_source (canvas_image, 0, 0);
+       cairo_context->set_operator (Cairo::OPERATOR_SOURCE);
+       cairo_context->paint ();
+
+#else
+
        Cairo::RefPtr<Cairo::Context> cairo_context = get_window()->create_cairo_context ();
        render (Rect (ev->area.x, ev->area.y, ev->area.x + ev->area.width, ev->area.y + ev->area.height), cairo_context);
-       return true;
-}
 
-/** @return Our Cairo context, or 0 if we don't have one */
-Cairo::RefPtr<Cairo::Context>
-GtkCanvas::context ()
-{
-       Glib::RefPtr<Gdk::Window> w = get_window ();
-       if (!w) {
-               return Cairo::RefPtr<Cairo::Context> ();
-       }
+#endif
 
-       return w->create_cairo_context ();
+       return true;
 }
 
 /** Handler for GDK scroll events.