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, 37 insertions, 0 deletions

diff --git a/libs/canvas/item.cc b/libs/canvas/item.cc
index 589f1214b7..98fe6362db 100644
--- a/libs/canvas/item.cc
+++ b/libs/canvas/item.cc
@@ -831,6 +831,43 @@ Item::render_children (Rect const & area, Cairo::RefPtr<Cairo::Context> context)
 }
 
 void
+Item::prepare_for_render_children (Rect const & area) const
+{
+	if (_items.empty()) {
+		return;
+	}
+
+	ensure_lut ();
+	std::vector<Item*> items = _lut->get (area);
+
+	for (std::vector<Item*>::const_iterator i = items.begin(); i != items.end(); ++i) {
+
+		if (!(*i)->visible ()) {
+			continue;
+		}
+
+		Rect item_bbox = (*i)->bounding_box ();
+
+		if (!item_bbox) {
+			continue;
+		}
+
+		Rect item = (*i)->item_to_window (item_bbox, false);
+		Rect d = item.intersection (area);
+
+		if (d) {
+			Rect draw = d;
+			if (draw.width() && draw.height()) {
+				(*i)->prepare_for_render (area);
+			}
+
+		} else {
+			// Item does not intersect with visible canvas area
+		}
+	}
+}
+
+void
 Item::add_child_bounding_boxes (bool include_hidden) const
 {
 	Rect self;