DrawingVisual performance with Opacity=0

Question

If I have a DrawingVisual in WPF with Opacity=0, is that enough for it not to be drawn? We have hundreds of DrawingVisuals on a Canvas, and are currently setting Opacity=0 on the visuals that are not to be displayed, and I wanted to make sure there is no rendering performance hit for rendering a DrawingVisual with Opacity=0.

UPDATE: I have discovered through testing that there IS overhead when Opacity=0, but since DrawingVisual doesn't have a Visibility property, I don't know how else you would tell it to not be displayed unless you actualy remove it from the visual tree, so any suggestions are welcome.

Answer 1

The best way to check would be to instead set the Visibility to Visibility.Colapsed, and see if there's any drawing performance differences.

Visibility.Colapsed ensures that the element is not visible but also that it will not participate in the Arrange, Measure and Render passes of the UI, while an element with Opacity=0 might participate in all passes.

Answer 2

I solved a very similar problem by using the DrawingGroup and adding or removing Drawing objects from the DrawingGroup as they either needed to be displayed or hidden. The key is to organize your Drawing objects in such a way that they are easy to manage and to understand how to add and remove them from the DrawingGroup. Remember that you want to add and remove the Drawing objexts from the DrawingGroup.Children. So use DrawingGroup.Children.Add(Drawing) and DrawingGroup.Children.Remove(Drawing). You will need to keep an external list of the Drawing objects you add/remove to the DrawingGroup to do this successfully.

See DrawingGroup Class and Drawing Class

I used this technique to great effect by drawing an Image (bitmap) into the first child in my instance of DrawingGroup and then adding and removing Drawing objects to this instance of DrawingGroup in order to layer polygons, paths, text, etc on top of the drawing.

I "draw" or "erase" on the image by adding or removing Drawing objects to the instance of the DrawingGroup. The DrawingGroup is treated as a single Drawing and so any scaling, panning, or other manipulations will affect all Drawing objects within the DrawingGroup.

Answer 3

Why not simply remove the visual from the visual children list? When it needs to be visible you add it back.