How to render bitmap into canvas in WPF?

Question

I've subclassed Canvas so that I can override its Render function. I need to know how I can load a bitmap in WPF and render that to the canvas. I'm completely new to WPF and I haven't found any tutorials that show you how to do something so seemingly trivial. Step-by-step instructions with examples would be great.

Answer 1

In WPF it is a rare case that you would need to override OnRender especially if all you wanted to do was draw a BMP to a background:

<Canvas>
    <Canvas.Background>
        <ImageBrush ImageSource="Resources\background.bmp" />
    </Canvas.Background>
    <!-- ... -->
</Canvas>

Answer 2

This should get you started:

class MyCanvas : Canvas {
   protected override void OnRender (DrawingContext dc) {
      BitmapImage img = new BitmapImage (new Uri ("c:\\demo.jpg"));
      dc.DrawImage (img, new Rect (0, 0, img.PixelWidth, img.PixelHeight));
   }
}

Answer 3

If you do want to paint background of canvas, I would recommend using ImageBrush as Background, 'coz that's simple as you dont need to subclass Canvas to override Onender.

But I'll give you a demo source-code for what you have asked:

Create a class (I've called it ImageCanvas)

    using System.Windows;
    using System.Windows.Controls;
    using System.Windows.Media;

    namespace WpfApplication1
    {
        public class ImageCanvas : Canvas
        {
            public ImageSource CanvasImageSource
            {
                get { return (ImageSource)GetValue(CanvasImageSourceProperty); }
                set { SetValue(CanvasImageSourceProperty, value); }
            }

            public static readonly DependencyProperty CanvasImageSourceProperty =
                DependencyProperty.Register("CanvasImageSource", typeof(ImageSource),
                typeof(ImageCanvas), new FrameworkPropertyMetadata(default(ImageSource)));

            protected override void OnRender(System.Windows.Media.DrawingContext dc)
            {
                dc.DrawImage(CanvasImageSource, new Rect(this.RenderSize));
                base.OnRender(dc);
            }
        }
    }

Now you can use it like this:

<Window x:Class="WpfApplication1.Window1"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:WpfApplication1" Title="Window1" Height="300" Width="300">
    <Grid>
        <local:ImageCanvas CanvasImageSource="/Splash.png">
            <TextBlock Text="Hello From Mihir!" />
        </local:ImageCanvas>
    </Grid>
</Window>