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How to: Hit Test Using a Win32 Host Container

You can create visual objects within a Win32 window by providing a host window container for the visual objects. To provide event handling for the contained visual objects you process the messages passed to the host window container’s message filter loop. Refer to Tutorial: Hosting Visual Objects in a Win32 Application for more information on how to host visual objects in a Win32 window.

The following code shows how to set up mouse event handlers for a Win32 window that is used as a host container for visual objects.

// Constant values from the "winuser.h" header file.
internal const int WM_LBUTTONUP = 0x0202,
                   WM_RBUTTONUP = 0x0205;

internal static IntPtr ApplicationMessageFilter(
    IntPtr hwnd, int message, IntPtr wParam, IntPtr lParam, ref bool handled)
    // Handle messages passed to the visual. 
    switch (message)
        // Handle the left and right mouse button up messages. 
        case WM_LBUTTONUP:
        case WM_RBUTTONUP:
            System.Windows.Point pt = new System.Windows.Point();
            pt.X = (uint)lParam & (uint)0x0000ffff;  // LOWORD = x
            pt.Y = (uint)lParam >> 16;               // HIWORD = y
            MyShape.OnHitTest(pt, message);

    return IntPtr.Zero;

The following example shows how to set up a hit test in response to trapping specific mouse events.

// Constant values from the "winuser.h" header file.
public const int WM_LBUTTONUP = 0x0202,
                 WM_RBUTTONUP = 0x0205;

// Respond to WM_LBUTTONUP or WM_RBUTTONUP messages by determining which visual object was clicked. 
public static void OnHitTest(System.Windows.Point pt, int msg)
    // Clear the contents of the list used for hit test results.

    // Determine whether to change the color of the circle or to delete the shape. 
    if (msg == WM_LBUTTONUP)
        MyWindow.changeColor = true;
    if (msg == WM_RBUTTONUP)
        MyWindow.changeColor = false;

    // Set up a callback to receive the hit test results enumeration.
                             new HitTestResultCallback(CircleHitTestResult),
                             new PointHitTestParameters(pt));

    // Perform actions on the hit test results list. 
    if (hitResultsList.Count > 0)

The HwndSource object presents Windows Presentation Foundation (WPF) content within a Win32 window. The value of the RootVisual property of the HwndSource object represents the top-most node in the visual tree hierarchy.

For the complete sample on hit testing objects using a Win32 host container, see Hit Test with Win32 Interoperation Sample.