c# - 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 的可见二维内容边界，而无需进行转换。但是，当转换 ModelVisual3D 时，GetDescendantBounds 返回比可见内容更大的边界。如何获取可见内容的准确边界？

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>

代码隐藏:

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

如果您可以在网格几何体中轻松找到所有三角形点而不会出现性能问题，您可以尝试下面的方法。我所做的是将所有 Point3D 转换为二维坐标并获取所有二维点的边界。

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);
}