[C#][WPF] How to save multiple canvas as an image?

Question

I am just looking around and tried to making a working version of saving multiple canvas as one image. For example would be nice to save them nearby each other, but I can not figure out how to do it.

public static void CreateSaveBitmap(Canvas canvas1, Canvas canvas2, string filename)
    {
        RenderTargetBitmap renderBitmap1 = new RenderTargetBitmap((int)canvas1.ActualWidth, (int)canvas1.ActualWidth, 96d, 96d, PixelFormats.Pbgra32);
        // needed otherwise the image output is black
        canvas1.Measure(new Size((int)canvas1.ActualWidth, (int)canvas1.ActualWidth));
        canvas1.Arrange(new Rect(new Size((int)canvas1.ActualWidth, (int)canvas1.ActualWidth)));

        renderBitmap1.Render(canvas1);

        RenderTargetBitmap renderBitmap2 = new RenderTargetBitmap((int)canvas2.ActualWidth, (int)canvas2.ActualWidth, 96d, 96d, PixelFormats.Pbgra32);
        // needed otherwise the image output is black
        canvas2.Measure(new Size((int)canvas2.ActualWidth, (int)canvas2.ActualWidth));
        canvas2.Arrange(new Rect(new Size((int)canvas2.ActualWidth, (int)canvas2.ActualWidth)));

        renderBitmap2.Render(canvas2);

        //JpegBitmapEncoder encoder = new JpegBitmapEncoder();
        PngBitmapEncoder encoder = new PngBitmapEncoder();

        encoder.Frames.Add(BitmapFrame.Create(renderBitmap1));
        encoder.Frames.Add(BitmapFrame.Create(renderBitmap2));
        using (FileStream file = File.Create(filename))
        {
            encoder.Save(file);
        }
    }

This is how I tried, but its only saving the first image. Can someone help me to solve this please?

UPDATE

I corrected some mistakes what told by @TheLethalCoder, and I also changed the output filetype to Tiff, but it doesn't helped. This is the latest version now:

public static void CreateSaveBitmap(Canvas canvas1, Canvas canvas2, string filename)
    {
        RenderTargetBitmap renderBitmap1 = new RenderTargetBitmap((int)canvas1.ActualWidth, (int)canvas1.ActualHeight, 96d, 96d, PixelFormats.Pbgra32);
        // needed otherwise the image output is black
        canvas1.Measure(new Size((int)canvas1.ActualWidth, (int)canvas1.ActualHeight));
        canvas1.Arrange(new Rect(new Size((int)canvas1.ActualWidth, (int)canvas1.ActualHeight)));

        renderBitmap1.Render(canvas1);

        RenderTargetBitmap renderBitmap2 = new RenderTargetBitmap((int)canvas2.ActualWidth, (int)canvas2.ActualHeight, 96d, 96d, PixelFormats.Pbgra32);
        // needed otherwise the image output is black
        canvas2.Measure(new Size((int)canvas2.ActualWidth, (int)canvas2.ActualHeight));
        canvas2.Arrange(new Rect(new Size((int)canvas2.ActualWidth, (int)canvas2.ActualHeight)));

        renderBitmap2.Render(canvas2);

        //JpegBitmapEncoder encoder = new JpegBitmapEncoder();
        TiffBitmapEncoder encoder = new TiffBitmapEncoder();

        encoder.Frames.Add(BitmapFrame.Create(renderBitmap1));
        encoder.Frames.Add(BitmapFrame.Create(renderBitmap2));
        using (FileStream file = File.Create(filename))
        {
            encoder.Save(file);
        }
    }

What type of image are you trying to save it as? And you're setting all your heights as widths — TheLethalCoder
– TheLethalCoder, Commented Oct 13, 2015 at 14:02
Oh png just saw it, try saving as a tiff or something that supports multiple frames... — TheLethalCoder
– TheLethalCoder, Commented Oct 13, 2015 at 14:04

King King · Accepted Answer · 2015-10-14 20:03:04Z

What you want is not multiple-frame image but to combine the images of your canvases by juxtaposing them. So actually you need just 1 Frame here but a big combined one. There are some ways to combine them but there is 1 simple way you can do with DrawingVisual. We can draw a Drawing on that visual and use RenderTargetBitmap to capture it. We use DrawingGroup to combine the ImageDrawings (from the 2 RenderTargetBitmaps). In summary, we have to do the following steps: from 2 RenderTargetBitmaps, you put them in 2 ImageDrawings and combine those into a DrawingGroup. Then you draw that combined Drawing on a DrawingVisual. Finally use RenderTargetBitmap to render that visual normally.

Here is the code you can try out:

public static void CreateSaveBitmap(Canvas canvas1, Canvas canvas2, string filename)
{
    RenderTargetBitmap renderBitmap1 = new RenderTargetBitmap((int)canvas1.ActualWidth, (int)canvas1.ActualHeight, 96d, 96d, PixelFormats.Pbgra32);

    canvas1.Measure(new Size((int)canvas1.ActualWidth, (int)canvas1.ActualHeight));
    canvas1.Arrange(new Rect(new Size((int)canvas1.ActualWidth, (int)canvas1.ActualHeight)));

    renderBitmap1.Render(canvas1);

    RenderTargetBitmap renderBitmap2 = new RenderTargetBitmap((int)canvas2.ActualWidth, (int)canvas2.ActualHeight, 96d, 96d, PixelFormats.Pbgra32);

    canvas2.Measure(new Size((int)canvas2.ActualWidth, (int)canvas2.ActualHeight));
    canvas2.Arrange(new Rect(new Size((int)canvas2.ActualWidth, (int)canvas2.ActualHeight)));

    renderBitmap2.Render(canvas2);

    //Combine the images here
    var dg = new DrawingGroup();
    var id1 = new ImageDrawing(renderBitmap1, 
                               new Rect(0,0,renderBitmap1.Width, renderBitmap1.Height));
    var id2 = new ImageDrawing(renderBitmap2,
                               new Rect(renderBitmap1.Width, 0
                                        renderBitmap2.Width,
                                        renderBitmap2.Height));
    dg.Children.Add(id1);
    dg.Children.Add(id2);
    var combinedImg = new RenderTargetBitmap((int)(renderBitmap1.Width + renderBitmap2.Width + 0.5),
                          (int)(Math.Max(renderBitmap1.Height, renderBitmap2.Height) + 0.5), 96, 96, PixelFormats.Pbgra32); 
    var dv = new DrawingVisual();
    using(var dc = dv.RenderOpen()){
       dc.DrawDrawing(dg);
    }
    combinedImg.Render(dv);

    //JpegBitmapEncoder encoder = new JpegBitmapEncoder();
    PngBitmapEncoder encoder = new PngBitmapEncoder();

    encoder.Frames.Add(BitmapFrame.Create(combinedImg));

    using (FileStream file = File.Create(filename)) {
        encoder.Save(file);
    }
}

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