Add an optional ArdourCanvas::Item::prepare_for_render interface

Called when an item has requested a redraw and intersects with visible
canvas area.

Also add Canvas::prepare_for_render that will call Item::prepare_for_render for
items visible on the canvas.

1 files changed, 6 insertions, 0 deletions

diff --git a/libs/canvas/canvas/container.h b/libs/canvas/canvas/container.h
index f95f2f9e2b..4f2fad8f60 100644
--- a/libs/canvas/canvas/container.h
+++ b/libs/canvas/canvas/container.h
@@ -53,6 +53,12 @@ public:
 	 *  (just call Item::render_children()). It can be overridden as necessary.
 	 */
 	void render (Rect const & area, Cairo::RefPtr<Cairo::Context> context) const;
+
+	/** The prepare_for_render() method is likely to be identical in all
+	 * containers (just call Item::prepare_for_render_children()). It can be
+	 * overridden as necessary.
+	 */
+	void prepare_for_render (Rect const & area) const;
 };
 
 }