WPF ModelVisual3D的可见2D内容范围

Question

In WPF, we can easily use VisualTreeHelper.GetDescendantBounds(Viewport3D) to get the visible 2D content bounds of a ModelVisual3D without transform. However, when the ModelVisual3D transfromed, GetDescendantBounds returns a bigger bounds than the visible content. How can I get the accurate bounds of the visible content?

Code-xaml:

<Grid Background="LightGray">
    <Viewport3D x:Name="MyViewport">
        <Viewport3D.Camera>
            <OrthographicCamera Position="3 3 5" LookDirection="-3 -3 -5" Width="3"/>
        </Viewport3D.Camera>
        <Viewport3D.Children>
            <ModelVisual3D>
                <ModelVisual3D.Content>
                    <DirectionalLight Color="White" Direction="-1 -1 -1"/>
                </ModelVisual3D.Content>
            </ModelVisual3D>
            <ModelVisual3D x:Name="MyVisual">
                <ModelVisual3D.Content>
                    <GeometryModel3D>
                        <GeometryModel3D.Geometry>
                            <MeshGeometry3D Positions="0,0,0 1,0,0 0,1,0 1,1,0 0,0,1 1,0,1 0,1,1 1,1,1"
                                            TriangleIndices="0,2,1 1,2,3 0,4,2 2,4,6 0,1,4 1,5,4 1,7,5 1,3,7 4,5,6 7,6,5 2,6,3 3,6,7"/>
                        </GeometryModel3D.Geometry>
                        <GeometryModel3D.Material>
                            <DiffuseMaterial Brush="Red"/>
                        </GeometryModel3D.Material>
                        <!--<GeometryModel3D.Transform>
                            <RotateTransform3D>
                                <RotateTransform3D.Rotation>
                                    <AxisAngleRotation3D Axis="1 1 0" Angle="5"/>
                                </RotateTransform3D.Rotation>
                            </RotateTransform3D>
                        </GeometryModel3D.Transform>-->
                    </GeometryModel3D>
                </ModelVisual3D.Content>
            </ModelVisual3D>
        </Viewport3D.Children>
    </Viewport3D>
    <Rectangle x:Name="MyRegion" Stroke="Blue" StrokeThickness="1" VerticalAlignment="Top" HorizontalAlignment="Left"/>
</Grid>

Code-behing:

var bounds = VisualTreeHelper.GetDescendantBounds(MyViewport);

MyRegion.Width = bounds.Width;
MyRegion.Height = bounds.Height;

MyRegion.Margin = new Thickness(bounds.Left, bounds.Top, 0, 0);

Answer 1

If you can easily find all triangle points without performance problem in your mesh geometry, you may try this method below. What I did is transforming all Point3Ds into 2D coordinates and get the bounds of all the 2D points.

GeneralTransform3DTo2D transform = MyVisual.TransformToAncestor(MyViewport);
MeshGeometry3D geometry = (MeshGeometry3D) ((GeometryModel3D) MyVisual.Content).Geometry;
Rect wholeBounds = Rect.Empty;
if (transform != null)
{
    for (int i = 0; i < geometry.TriangleIndices.Count;)
    {
        Polygon p = new Polygon
        {
            Stroke = Brushes.Blue,
            StrokeThickness = 0.25
        };
        var tr = ((GeometryModel3D) MyVisual.Content).Transform;
        p.Points.Add(transform.Transform(tr.Transform(geometry.Positions[geometry.TriangleIndices[i++]])));
        p.Points.Add(transform.Transform(tr.Transform(geometry.Positions[geometry.TriangleIndices[i++]])));
        p.Points.Add(transform.Transform(tr.Transform(geometry.Positions[geometry.TriangleIndices[i++]])));
        foreach (Point point in p.Points)
        {
            wholeBounds.Union(point);
        }
    }
    MyRegion.Width = wholeBounds.Width;
    MyRegion.Height = wholeBounds.Height;

    MyRegion.Margin = new Thickness(wholeBounds.Left, wholeBounds.Top, 0, 0);
}

Answer 2

I improved @walterlv's method to satisfy more complex hierarchies.

private void MainWindow_OnMouseDoubleClick(object sender, MouseButtonEventArgs e)
{
    var bounds = CalculateBounds(MyVisual);

    MyRegion.Width = bounds.Width;
    MyRegion.Height = bounds.Height;

    MyRegion.Margin = new Thickness(bounds.Left, bounds.Top, 0, 0);
}

public static Viewport3DVisual GetViewport3DVisual(Visual3D visual3D)
{
    DependencyObject obj = visual3D;

    while (obj != null)
    {
        var visual = obj as Viewport3DVisual;
        if (visual != null)
        {
            return visual;
        }

        obj = VisualTreeHelper.GetParent(obj);
    }

    return null;
}

public static Rect CalculateBounds(Visual3D visual)
{
    var transform = visual.TransformToAncestor(GetViewport3DVisual(visual));
    if (transform == null)
    {
        return Rect.Empty;
    }

    var bounds = Rect.Empty;

    var modelVisual3D = visual as ModelVisual3D;
    if (modelVisual3D != null)
    {
        bounds.Union(CalculateBounds(transform, modelVisual3D.Content, Matrix3D.Identity));

        // Unio the bounds of Children
        foreach (var child in modelVisual3D.Children)
        {
            bounds.Union(CalculateBounds(child));
        }
    }
    else
    {
        // UIElement3D or Viewport2DVisual3D 
        bounds.Union(transform.TransformBounds(VisualTreeHelper.GetDescendantBounds(visual)));
    }

    return bounds;
}

public static Rect CalculateBounds(GeneralTransform3DTo2D transform, Model3D model, Matrix3D rootMatrix)
{
    var region = Rect.Empty;
    var matrix = Matrix3D.Identity;

    matrix.Prepend(rootMatrix);
    if (model.Transform != null)
    {
        matrix.Prepend(model.Transform.Value);
    }

    var geometryModel3D = model as GeometryModel3D;
    if (geometryModel3D != null)
    {
        var meshGeometry3D = geometryModel3D.Geometry as MeshGeometry3D;
        if (meshGeometry3D != null)
        {
            var innerTransform = new MatrixTransform3D(matrix);
            foreach (var position in meshGeometry3D.Positions)
            {
                region.Union(transform.Transform(innerTransform.Transform(position)));
            }
        }
    }
    else
    {
        var model3DGroup = model as Model3DGroup;
        if (model3DGroup != null)
        {
            foreach (var child in model3DGroup.Children)
            {
                region.Union(CalculateBounds(transform, child, matrix));
            }
        }
    }

    return region;
}