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How to: Hit Test Geometry in a Visual

This example shows how to perform a hit test on a visual object that is composed of one or more Geometry objects.

Example

The following example shows how to retrieve the DrawingGroup from a visual object that uses the GetDrawing method. A hit test is then performed on the rendered content of each drawing in the DrawingGroup to determine which geometry was hit.

NoteNote:

In most cases, you would use the HitTest method to determine whether a point intersects any of the rendered content of a visual.

// Determine if a geometry within the visual was hit.
static public void HitTestGeometryInVisual(Visual visual, Point pt)
{
    // Retrieve the group of drawings for the visual.
    DrawingGroup drawingGroup = VisualTreeHelper.GetDrawing(visual);
    EnumDrawingGroup(drawingGroup, pt);
}

// Enumerate the drawings in the DrawingGroup.
static public void EnumDrawingGroup(DrawingGroup drawingGroup, Point pt)
{
    DrawingCollection drawingCollection = drawingGroup.Children;

    // Enumerate the drawings in the DrawingCollection.
    foreach (Drawing drawing in drawingCollection)
    {
        // If the drawing is a DrawingGroup, call the function recursively.
        if (drawing.GetType() == typeof(DrawingGroup))
        {
            EnumDrawingGroup((DrawingGroup)drawing, pt);
        }
        else if (drawing.GetType() == typeof(GeometryDrawing))
        {
            // Determine whether the hit test point falls within the geometry.
            if (((GeometryDrawing)drawing).Geometry.FillContains(pt))
            {
                // Perform action based on hit test on geometry.
            }
        }

    }
}

The FillContains method is an overloaded method that allows you to hit test by using a specified Point or Geometry. If a geometry is stroked, the stroke can extend outside the fill bounds. In which case, you may want to call StrokeContains in addition to FillContains.

You can also provide a ToleranceType that is used for the purposes of Bezier flattening.

NoteNote:

This sample does not take into account any transforms or clipping that may be applied to the geometry. In addition, this sample will not work with a styled control, since it does not have any drawings directly associated with it.

See Also

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