Rendering WPF DrawingGroup to single ImageSource

Question

Currently I'm using a System.Windows.Media.DrawingGroup to store some tiled images (ImageDrawing) inside the Children-DrawingCollection property. Well the problem is now, this method gets really slow if you display the entire DrawingGroup in an Image control, because my DrawingGroup can contain hundreds or even thousands of small images it can really mess up the performance.

So my first thought was to somehow render a single image from all the small ones inside the DrawingGroup and then only display that image, that would be much faster. But as you might have figured out I haven't found any solution so simply combine several images with WPF Imaging.

It would really be great if someone could help with this problem or tell me how i can improve the performance with the DrawingGroup or even use another approach.

One last thing, currently I'm using a RenderTargetBitmap to generate a single BitmapSource from the DrawingGroup, this approach isn't really faster, but it makes the scrolling and working on the Image control at least a little smoother.

Answer 1

I'm working on a problem having to do with tiled images, with the added complication of having to display some images overlaid on others.

I haven't run into any performance issues (and likely won't since my images are rather small and relatively small in number, around 100 max.), but I did come across the Freeze method in a code sample for the DrawingImage class. The comment for it was "Freeze the DrawingImage for performance benefits."

The Freeze method also applies to the DrawingGroup class. Maybe give it a try?

Answer 2

I'm not sure this applies to your problem, but I'll post it here anyway since it might help someone:

If not all of the images in the drawing group is going to be visible at the same time, you could set the ClipGeometry property to whatever you want it to draw. This effectively tells WPF that the parts outside of the geometry is not needed and will be skipped during rendering.

A few other things you could experiment with are:

• Freeze the drawinggroup before applying it to your image source. At least it couldn't hurt (unless you really need to modify the instance, but remember you could always just create a new one instead of modifying the old)
• Try different ways to display your drawinggroup. For instance as a DrawingVisual (which is considered light weight) or as a DrawingBrush to paint e.g. a rectangle.
• Combine the small images into smaller groups which you then combine to your bigger group. No idea if this improves or hurts performance, but it could be worth trying.