How to: Hit Test in a Viewport3D

This example shows how to hit test for 3D Visuals in a Viewport3D.

Because HitTest returns 2D and 3D information, it is possible to iterate through the test results to read only 3D results.

public void HitTest(object sender, System.Windows.Input.MouseButtonEventArgs args)
    Point mouseposition = args.GetPosition(myViewport);
    Point3D testpoint3D = new Point3D(mouseposition.X, mouseposition.Y, 0);
    Vector3D testdirection = new Vector3D(mouseposition.X, mouseposition.Y, 10);
    PointHitTestParameters pointparams = new PointHitTestParameters(mouseposition);
    RayHitTestParameters rayparams = new RayHitTestParameters(testpoint3D, testdirection);

    //test for a result in the Viewport3D
    VisualTreeHelper.HitTest(myViewport, null, HTResult, pointparams);

The HitTestResultBehavior in the following code determines how the hit test results are processed. UpdateResultInfo and UpdateMaterial are locally-defined methods.

public HitTestResultBehavior HTResult(System.Windows.Media.HitTestResult rawresult)
    RayHitTestResult rayResult = rawresult as RayHitTestResult;

    if (rayResult != null)
        RayMeshGeometry3DHitTestResult rayMeshResult = rayResult as RayMeshGeometry3DHitTestResult;

        if (rayMeshResult != null)
            GeometryModel3D hitgeo = rayMeshResult.ModelHit as GeometryModel3D;

            UpdateMaterial(hitgeo, (side1GeometryModel3D.Material as MaterialGroup));

    return HitTestResultBehavior.Continue;