How to render a WPF UserControl to a bitmap without creating a window

How can I render a WPF UserControl to a bitmap without creating a window? I need to render a WPF UserControl and upload it to another program. The bitmaps will be rendered through a Windows Service, so creating a window is not an option (I know there's ways to 'virtually' create windows, but unfortunately anything that calls a command to create a window is NOT an option in my case). Is there a way to RENDER the UserControl without binding it to a Window?

Solution 1:

Have you tried spinning up an instance of the user control and doing something like this:

UserControl control = new UserControl1();

control.Measure(new Size(300, 300));
control.Arrange(new Rect(new Size(300,300)));

RenderTargetBitmap bmp = new RenderTargetBitmap(300, 300, 96, 96, PixelFormats.Pbgra32);

bmp.Render(control);

var encoder = new PngBitmapEncoder();

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

using (Stream stm = File.Create(@"c:\test.png"))
   encoder.Save(stm);

It looks like you need to Measure, Arrange. This worked for me.

Solution 2:

Ended up using an HwndHost with no actual window.

void cwind()
    {
        Application myapp = new Application();
        mrenderer = new WPFRenderer();
        mrenderer.Width = 256;
        mrenderer.Height = 256;

        HwndSourceParameters myparms = new HwndSourceParameters();
        HwndSource msrc = new HwndSource(myparms);
        myparms.HwndSourceHook = new HwndSourceHook(ApplicationMessageFilter);

        msrc.RootVisual = mrenderer;
        myapp.Run();
    }
    static IntPtr ApplicationMessageFilter(
IntPtr hwnd, int message, IntPtr wParam, IntPtr lParam, ref bool handled)
    {
        return IntPtr.Zero;
    }

Solution 3:

Apparently, if you call control.UpdateLayout() after measuring and arranging, the user control doesn't need to be in any window.

Solution 4:

Based on IDWMaster's solution I did it a bit differently using the System.Windows.Forms.UserControl. Otherwise the bindings were not up-to-date when the export to bitmap happened. This works for me (this is the WPF control to render):

System.Windows.Forms.UserControl controlContainer = new System.Windows.Forms.UserControl();
controlContainer.Width = width;
controlContainer.Height = height;
controlContainer.Load += delegate(object sender, EventArgs e)
{
    this.Dispatcher.BeginInvoke((Action)delegate
    {
        using (FileStream fs = new FileStream(path, FileMode.Create))
        {
            RenderTargetBitmap bmp = new RenderTargetBitmap(width, height, 96, 96, PixelFormats.Pbgra32);
            bmp.Render(this);
            BitmapEncoder encoder = new PngBitmapEncoder();
            encoder.Frames.Add(BitmapFrame.Create(bmp));
            encoder.Save(fs);
            controlContainer.Dispose();
        }
    }, DispatcherPriority.Background);
};

controlContainer.Controls.Add(new ElementHost() { Child = this, Dock = System.Windows.Forms.DockStyle.Fill });
IntPtr handle = controlContainer.Handle;