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.
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.
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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.
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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. |
