WPF ModelVisual3D的可见2D内容边界

Question

在WPF中，我们可以轻松地使用VisualTreeHelper.GetDescendantBounds(Viewport3D)来获取ModelVisual3D的可见2D内容边界（无变换）。然而，当ModelVisual3D有变换时，GetDescendantBounds返回的边界比可见内容要大。如何才能准确地获取可见内容的边界呢？

代码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>

代码后台:

var bounds = VisualTreeHelper.GetDescendantBounds(MyViewport);

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

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

- Iron

Answer 1

如果您的网格几何中能够轻松找到所有三角形点而不会出现性能问题，那么您可以尝试下面的方法。我的做法是将所有Point3Ds转换为2D坐标，并获取所有2D点的边界。

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);
}

- walterlv

---

请注意，我使用“多边形”来显示屏幕上的线条，以展示如何解决您的问题。如果您只想显示外部边界，则无需使用它。顺便说一下，所有点都在“矩形”中联合了三次。 - walterlv

谢谢。它运行得非常好。我刚刚改进了你的方法，以满足更复杂的层次结构。 - Iron

Answer 2

我改进了@walterlv的方法，以满足更复杂的层级结构。

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;
} 

- Iron