Frames per second using WPF's DrawingContext class

I've got an example app which draws Rectangles, Lines etc. using the DrawContext instance of the OnRender override of a Control class. This control is repainted every 10 milliseconds by calling InvalidateVisual (I can post the source to anybody who's interested). I calculate the Frames per second (FPS) by measuring the time between each call of OnRender.

However, this figure for FPS is incorrect. Just by looking at the app I can see that the figure given for FPS is higher than the number of times per second that the app repaints itself. This is because "When you use a DrawingContext object's draw commands, you are actually storing a set of rendering instructions (although the exact storage mechanism depends on the type of object that supplies the DrawingContext) that will later be used by the graphics system; you are not drawing to the screen in real-time."

So what I would like to know is if there is any event I can subscribe to, or any other way, to ascertain how m开发者_C百科any times per second my WPF app/control is generating a new bitmap and drawing it to the screen? Is there any bitmap buffer held by the "graphics system" which we can access?

Many thanks!

What you need to use is the CompositionTarget.Rendering event that is called every frame.