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

Question

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?

Perhaps you could supply a little more information. If the User Control can't be rendered, why does it even exist? It is a visual element. — Steve Wellens, Mar 04 '11 at 03:29
It needs to be rendered, but not directly to a display (so there can be no window). It's being rendered to an OpenGL cube. The cube rendering works, but currently I have to create a separate window to do the rendering in. It would be nice if I didn't need a separate window for the WPF rendering. — bbosak, Mar 04 '11 at 03:34

RQDQ · Answer 1 · 2011-03-04T14:25:59.497

70

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.

edited Mar 04 '11 at 14:25

answered Mar 04 '11 at 03:00

RQDQ

15,461
2
32
59

2

Google search to export a user control to a JPG brought me here and this answer was perfect. Thanks very much. – Richard Powell Feb 27 '14 at 11:03
1

This works really well however underlying styles are not properly applied to the user control. I'm not sure how to overcome that at the moment, otherwise a perfect solution! – JT_ Jan 13 '15 at 09:13
1

To make this work, did you have to have the control previously displayed? I am creating a window and will get black output unless I previously Show() and Close() the window. – Steve Robbins Jun 10 '16 at 20:24
4

If it helps someone, calling `control.UpdateLayout()` immediately after `Arrange()` did the trick for me. – dotNET Oct 20 '16 at 12:01
@SteveRobbins Interestingly enough, I got the same result you did when calling this from my main method on the control itself. But when I moved the code into the Control and just called the method on the specific element (i.e. specific Control within my control that I wanted) it behaved as described. This is in addition to having to call control.UpdateLayout() per (at)dotNET's suggestion so that it had my data from my DataContext instead of just a blank grid. – claudekennilol May 15 '18 at 19:02

score 8 · Accepted Answer · answered Mar 04 '11 at 22:43

8

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;
    }

answered Mar 04 '11 at 22:43

bbosak

5,353
7
42
60

1

I had to modify your solution a bit to make it work for me, but using a Win32 wrapper to force WPF to load in a hidden window is a great idea. – floele Nov 19 '12 at 08:54
@floele: maybe for some solutions, a `Win32` wrapper is a great idea. But in this case, I think @RQDQ has the proper solution. – IAbstract Aug 15 '15 at 21:15
2

Please tell me What is WPFRenderer? (where is that assembly file and namespace) – Maria Jul 17 '16 at 12:50
Two comments: 1) WPFRenderer appears to be a custom UserControl. 2) This solution is the best because it supports Bindings. Simply creating, measuring, and arranging a UserControl (as @RQDQ) has suggested is a simpler, more elegant solution but does not support Bindings. So I guess it depends on your use case what you should do. – Tim Cooke Jan 21 '17 at 15:03
This is also the solution if you want to render animations \ storyboards in your xaml. – BryanJ Apr 11 '17 at 03:12

score 4 · Answer 3 · answered Mar 05 '15 at 14:49

4

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

answered Mar 05 '15 at 14:49

Jiří Skála

649
9
23

score 1 · Answer 4 · answered Nov 19 '12 at 08:58

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;

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

4 Answers4

Linked