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

I've created and succesfully tested a working method by using the 3DUtils Codeplex source library.

The real work is performed in the TryWorldToViewportTransform() method from 3DUtils. This method will not work without it (see the above link).

Very useful information was also found in the article by Eric Sink: Auto-Zoom.

NB. There may be more reliable/efficient approaches, if so please add them as an answer. In the meantime this is good enough for my needs.

    /// 

    /// Takes a 3D point and returns the corresponding 2D point (X,Y) within the viewport.  
    /// Requires the 3DUtils project available at http://www.codeplex.com/Wiki/View.aspx?ProjectName=3DTools
    /// 
    /// A point in 3D space
    /// An instance of Viewport3D
    /// The corresponding 2D point or null if it could not be calculated
    public Point? Point3DToScreen2D(Point3D point3D, Viewport3D viewPort)
    {
        bool bOK = false;

        // We need a Viewport3DVisual but we only have a Viewport3D.
        Viewport3DVisual vpv =VisualTreeHelper.GetParent(viewPort.Children[0]) as Viewport3DVisual;

        // Get the world to viewport transform matrix
        Matrix3D m = MathUtils.TryWorldToViewportTransform(vpv, out bOK);

        if (bOK)
        {
            // Transform the 3D point to 2D
            Point3D transformedPoint = m.Transform(point3D);

            Point screen2DPoint = new Point(transformedPoint.X, transformedPoint.Y);

            return new Nullable(screen2DPoint);
        }
        else
        {
            return null; 
        }
    }