How to improve Canvas rendering performance?

Question

I have to draw a lot of Shape (about 1/2 hundred thousand) as [Canvas][2]'s childrens. I make this in my WPF application dividing work in two parts: first thing I create shapes by setting the properties of each of them (like Margin, Fill, Width, etc...), after I add shapes as Canvas's children.

MyCanvas.Children.Add(MyShape)

Now i want to improve the performance of the second part, because when i draw the shapes my application is blocked for a long period of time. So i tried to use the Dispatcher and its method [BeginInvoke][4] with different [priorities][5]: only if I use the Background priority the main application does not block, otherwise the application remains blocked and the "picture" is not displayed until all shapes are added to my Canvas, but if I use the Background priority obviously everything is slower. I also tried to create a new thread instead of using the Dispatcher, but there was no significant change.

How can I fix this problem, and generally improve the performance of my application when I add my shapes to Canvas?

Thanks.

Answer 1

Need to use Visual objects instead of Shape; in particular, as suggested, DrawingVisual: a visual object that can be used to render vector graphics. In fact, as written in the MSDN library:

DrawingVisual is a lightweight drawing class that is used to render shapes, images, or text. This class is considered lightweight because it does not provide layout, input, focus, or event handling, which improves its performance. For this reason, drawings are ideal for backgrounds and clip art.

So, for example, to create a DrawingVisual that contains a rectangle:

private DrawingVisual CreateDrawingVisualRectangle()
{
   DrawingVisual drawingVisual = new DrawingVisual();

   // Retrieve the DrawingContext in order to create new drawing content.
   DrawingContext drawingContext = drawingVisual.RenderOpen();

   // Create a rectangle and draw it in the DrawingContext.
   Rect rect = new Rect(new System.Windows.Point(160, 100), new System.Windows.Size(320, 80));
   drawingContext.DrawRectangle(System.Windows.Media.Brushes.LightBlue, (System.Windows.Media.Pen)null, rect);

   // Persist the drawing content.
   drawingContext.Close();

   return drawingVisual;
}

In order to use DrawingVisual objects, you need to create a host container for the objects. The host container object must derive from the FrameworkElement class, which provides the layout and event handling support that the DrawingVisual class lacks. When you create a host container object for visual objects, you need to store the visual object references in a VisualCollection.

public class MyVisualHost : FrameworkElement
{
   // Create a collection of child visual objects.
   private VisualCollection _children;

   public MyVisualHost()
   {
       _children = new VisualCollection(this);
       _children.Add(CreateDrawingVisualRectangle());

       // Add the event handler for MouseLeftButtonUp.
       this.MouseLeftButtonUp += new System.Windows.Input.MouseButtonEventHandler(MyVisualHost_MouseLeftButtonUp);
   }
}

The event handling routine can then implement hit testing by invoking the HitTest method. The method's HitTestResultCallback parameter refers to a user-defined procedure that you can use to determine the resulting action of a hit test.