WPF RenderTargetBitmap with Viewport3D

Question

I'm loading a XAML UserControl with XamlReader and then I'm trying to convert it to an image with RenderTargetBitmap.

It's working fine with a simple UserControl.

But if I use this Viewport3D, it doesn't work. The image is created without the 3D part... :

    <Viewport3D>
        <ModelVisual3D>
            <ModelVisual3D.Content>
                <GeometryModel3D>
                    <GeometryModel3D.Geometry>
                        <MeshGeometry3D
                            Positions="-0.5  0.5  -0.5,  0.5  0.5  -0.5,
                                       -0.5  0  0.5,  0.5  0  0.5"
                            TriangleIndices=" 0  2  1,  1  2  3"
                            TextureCoordinates="0 0, 1 0, 0 1, 1 1" />
                    </GeometryModel3D.Geometry>

                    <GeometryModel3D.Material>
                        <DiffuseMaterial>
                            <DiffuseMaterial.Brush>
                                <VisualBrush>
                                    <VisualBrush.Visual>
                                        <Button>Hi</Button>
                                    </VisualBrush.Visual>
                                </VisualBrush>
                            </DiffuseMaterial.Brush>
                        </DiffuseMaterial>                              
                    </GeometryModel3D.Material>

                    <!-- Non-Affine Matrix Transform. -->
                    <GeometryModel3D.Transform>
                        <MatrixTransform3D>
                        </MatrixTransform3D>
                    </GeometryModel3D.Transform>

                </GeometryModel3D>
            </ModelVisual3D.Content>
        </ModelVisual3D>

        <!-- Light sources. -->
        <ModelVisual3D>
            <ModelVisual3D.Content>
                <Model3DGroup>
                    <AmbientLight Color="#404040" />
                    <DirectionalLight Color="#C0C0C0" Direction="0 -2 -1" />
                </Model3DGroup>
            </ModelVisual3D.Content>
        </ModelVisual3D>

        <!-- Camera. -->
        <Viewport3D.Camera>
            <PerspectiveCamera Position="0 0.2 1"
                               LookDirection="0 0 -1.5"
                               UpDirection="0 1 0"
                               FieldOfView="100">
            </PerspectiveCamera>
        </Viewport3D.Camera>
    </Viewport3D>

My method to convert a UserControl to an image :

private static byte[] ConvertUserControlToPng(UserControl userControl)
    {
        userControl.Measure(new Size(userControl.Width, userControl.Height));
        userControl.Arrange(new Rect(new Size(userControl.Width, userControl.Height)));
        var renderTargetBitmap = new RenderTargetBitmap((int)(userControl.Width * 300 / 96),
                                                        (int)(userControl.Height * 300 / 96),
                                                        300, 300, PixelFormats.Pbgra32);
        renderTargetBitmap.Render(userControl);
        BitmapEncoder encoder = new PngBitmapEncoder();
        encoder.Frames.Clear();
        encoder.Frames.Add(BitmapFrame.Create(renderTargetBitmap));

        byte[] result;
        using (var stream = new MemoryStream())
        {
            encoder.Save(stream);
            result = stream.ToArray();
        }
        return result;
    }

Am I missing something ?

Answer 1

I was able to get something visible in a png save to a file, I just added a call to UpdateLayout() after the calls to Measure and Arrange:

var viewport= (Viewport3D)XamlReader.Parse("... xaml ....");

viewport.Measure(new Size(viewport.Width, viewport.Height));
viewport.Arrange(new Rect(new Size(viewport.Width, viewport.Height)));
viewport.UpdateLayout();

var renderTargetBitmap = new RenderTargetBitmap((int)viewport.Width * 300 / 96,
                                                (int)viewport.Height * 300 / 96,
                                                300, 300, PixelFormats.Pbgra32);

renderTargetBitmap.Render(viewport);
BitmapEncoder encoder = new PngBitmapEncoder();
encoder.Frames.Clear();
encoder.Frames.Add(BitmapFrame.Create(renderTargetBitmap));
encoder.Save(new FileStream(@"D:\Test.png", FileMode.Create, FileAccess.Write));

Answer 2

So, my guess is that it is somewhat virtualized with the rendering. Maybe not -- but the best thing I can notice in your code above is that it's using a UserControl -- not a Control (Viewport3D). When you run the code, does it make it through it at all? Or does it throw an exception?