Projecting a 3D point to a 2D screen coordinate

Question

Based on information in Chapter 7 of 3D Programming For Windows (Charles Petzold), I\'ve attempted to write as helper function that projects a Point3D to a standard 2D Point

Answer 1

This doesn't address the algoritm in question but it may be useful for peple coming across this question (as I did).

In .NET 3.5 you can use Visual3D.TransformToAncestor(Visual ancestor). I use this to draw a wireframe on a canvas over my 3D viewport:

    void CompositionTarget_Rendering(object sender, EventArgs e)
    {
        UpdateWireframe();
    }

    void UpdateWireframe()
    {
        GeometryModel3D model = cube.Content as GeometryModel3D;

        canvas.Children.Clear();

        if (model != null)
        {
            GeneralTransform3DTo2D transform = cube.TransformToAncestor(viewport);
            MeshGeometry3D geometry = model.Geometry as MeshGeometry3D;

            for (int i = 0; i < geometry.TriangleIndices.Count;)
            {
                Polygon p = new Polygon();
                p.Stroke = Brushes.Blue;
                p.StrokeThickness = 0.25;
                p.Points.Add(transform.Transform(geometry.Positions[geometry.TriangleIndices[i++]]));
                p.Points.Add(transform.Transform(geometry.Positions[geometry.TriangleIndices[i++]]));
                p.Points.Add(transform.Transform(geometry.Positions[geometry.TriangleIndices[i++]]));
                canvas.Children.Add(p);
            }
        }
    }

This also takes into account any transforms on the model etc.

See also: http://blogs.msdn.com/wpf3d/archive/2009/05/13/transforming-bounds.aspx