Tutorial: Hosting Visual Objects in a Win32 Application

Windows Presentation Foundation (WPF) provides a rich environment for creating applications. However, when you have a substantial investment in Win32 code, it might be more effective to add WPF functionality to your application rather than rewrite your code. To provide support for Win32 and WPF graphics subsystems used concurrently in an application, WPF provides a mechanism for hosting objects in a Win32 window.

This tutorial describes how to write a sample application, Hit Test with Win32 Interoperation Sample, that hosts WPF visual objects in a Win32 window.

Requirements

This tutorial assumes a basic familiarity with both WPF and Win32 programming. For a basic introduction to WPF programming, see Walkthrough: My first WPF desktop application. For an introduction to Win32 programming, see any of the numerous books on the subject, in particular Programming Windows by Charles Petzold.

Note

This tutorial includes a number of code examples from the associated sample. However, for readability, it does not include the complete sample code. For the complete sample code, see Hit Test with Win32 Interoperation Sample.

Creating the Host Win32 Window

The key to hosting WPF objects in a Win32 window is the HwndSource class. This class wraps the WPF objects in a Win32 window, allowing them to be incorporated into your user interface (UI) as a child window.

The following example shows the code for creating the HwndSource object as the Win32 container window for the visual objects. To set the window style, position, and other parameters for the Win32 window, use the HwndSourceParameters object.

// Constant values from the "winuser.h" header file.
internal const int WS_CHILD = 0x40000000,
                   WS_VISIBLE = 0x10000000;

internal static void CreateHostHwnd(IntPtr parentHwnd)
{
    // Set up the parameters for the host hwnd.
    HwndSourceParameters parameters = new HwndSourceParameters("Visual Hit Test", _width, _height);
    parameters.WindowStyle = WS_VISIBLE | WS_CHILD;
    parameters.SetPosition(0, 24);
    parameters.ParentWindow = parentHwnd;
    parameters.HwndSourceHook = new HwndSourceHook(ApplicationMessageFilter);

    // Create the host hwnd for the visuals.
    myHwndSource = new HwndSource(parameters);

    // Set the hwnd background color to the form's background color.
    myHwndSource.CompositionTarget.BackgroundColor = System.Windows.Media.Brushes.OldLace.Color;
}
' Constant values from the "winuser.h" header file.
Friend Const WS_CHILD As Integer = &H40000000, WS_VISIBLE As Integer = &H10000000

Friend Shared Sub CreateHostHwnd(ByVal parentHwnd As IntPtr)
    ' Set up the parameters for the host hwnd.
    Dim parameters As New HwndSourceParameters("Visual Hit Test", _width, _height)
    parameters.WindowStyle = WS_VISIBLE Or WS_CHILD
    parameters.SetPosition(0, 24)
    parameters.ParentWindow = parentHwnd
    parameters.HwndSourceHook = New HwndSourceHook(AddressOf ApplicationMessageFilter)

    ' Create the host hwnd for the visuals.
    myHwndSource = New HwndSource(parameters)

    ' Set the hwnd background color to the form's background color.
    myHwndSource.CompositionTarget.BackgroundColor = System.Windows.Media.Brushes.OldLace.Color
End Sub

Note

The value of the ExtendedWindowStyle property cannot be set to WS_EX_TRANSPARENT. This means that the host Win32 window cannot be transparent. For this reason, the background color of the host Win32 window is set to the same background color as its parent window.

Adding Visual Objects to the Host Win32 Window

Once you have created a host Win32 container window for the visual objects, you can add visual objects to it. You will want to ensure that any transformations of the visual objects, such as animations, do not extend beyond the bounds of the host Win32 window's bounding rectangle.

The following example shows the code for creating the HwndSource object and adding visual objects to it.

Note

The RootVisual property of the HwndSource object is set to the first visual object added to the host Win32 window. The root visual object defines the top-most node of the visual object tree. Any subsequent visual objects added to the host Win32 window are added as child objects.

public static void CreateShape(IntPtr parentHwnd)
{
    // Create an instance of the shape.
    MyShape myShape = new MyShape();

    // Determine whether the host container window has been created.
    if (myHwndSource == null)
    {
        // Create the host container window for the visual objects.
        CreateHostHwnd(parentHwnd);

        // Associate the shape with the host container window.
        myHwndSource.RootVisual = myShape;
    }
    else
    {
        // Assign the shape as a child of the root visual.
        ((ContainerVisual)myHwndSource.RootVisual).Children.Add(myShape);
    }
}
Public Shared Sub CreateShape(ByVal parentHwnd As IntPtr)
    ' Create an instance of the shape.
    Dim myShape As New MyShape()

    ' Determine whether the host container window has been created.
    If myHwndSource Is Nothing Then
        ' Create the host container window for the visual objects.
        CreateHostHwnd(parentHwnd)

        ' Associate the shape with the host container window.
        myHwndSource.RootVisual = myShape
    Else
        ' Assign the shape as a child of the root visual.
        CType(myHwndSource.RootVisual, ContainerVisual).Children.Add(myShape)
    End If
End Sub

Implementing the Win32 Message Filter

The host Win32 window for the visual objects requires a window message filter procedure to handle messages that are sent to the window from the application queue. The window procedure receives messages from the Win32 system. These may be input messages or window-management messages. You can optionally handle a message in your window procedure or pass the message to the system for default processing.

The HwndSource object that you defined as the parent for the visual objects must reference the window message filter procedure you provide. When you create the HwndSource object, set the HwndSourceHook property to reference the window procedure.

parameters.HwndSourceHook = new HwndSourceHook(ApplicationMessageFilter);
parameters.HwndSourceHook = New HwndSourceHook(AddressOf ApplicationMessageFilter)

The following example shows the code for handling the left and right mouse button up messages. The coordinate value of the mouse hit position is contained in the value of the lParam parameter.

// 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);
            break;
    }

    return IntPtr.Zero;
}
' Constant values from the "winuser.h" header file.
Friend Const WM_LBUTTONUP As Integer = &H202, WM_RBUTTONUP As Integer = &H205

Friend Shared Function ApplicationMessageFilter(ByVal hwnd As IntPtr, ByVal message As Integer, ByVal wParam As IntPtr, ByVal lParam As IntPtr, ByRef handled As Boolean) As IntPtr
    ' Handle messages passed to the visual.
    Select Case message
        ' Handle the left and right mouse button up messages.
        Case WM_LBUTTONUP, WM_RBUTTONUP
            Dim pt As New System.Windows.Point()
            pt.X = CUInt(lParam) And CUInt(&HFFFF) ' LOWORD = x
            pt.Y = CUInt(lParam) >> 16 ' HIWORD = y
            MyShape.OnHitTest(pt, message)
    End Select

    Return IntPtr.Zero
End Function

Processing the Win32 Messages

The code in the following example shows how a hit test is performed against the hierarchy of visual objects contained in the host Win32 window. You can identify whether a point is within the geometry of a visual object, by using the HitTest method to specify the root visual object and the coordinate value to hit test against. In this case, the root visual object is the value of the RootVisual property of the HwndSource object.

// 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.
    hitResultsList.Clear();

    // 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.
    VisualTreeHelper.HitTest(MyWindow.myHwndSource.RootVisual,
                             null,
                             new HitTestResultCallback(CircleHitTestResult),
                             new PointHitTestParameters(pt));

    // Perform actions on the hit test results list.
    if (hitResultsList.Count > 0)
    {
        ProcessHitTestResultsList();
    }
}
' Constant values from the "winuser.h" header file.
Public Const WM_LBUTTONUP As Integer = &H0202, WM_RBUTTONUP As Integer = &H0205

' Respond to WM_LBUTTONUP or WM_RBUTTONUP messages by determining which visual object was clicked.
Public Shared Sub OnHitTest(ByVal pt As System.Windows.Point, ByVal msg As Integer)
	' Clear the contents of the list used for hit test results.
	hitResultsList.Clear()

	' Determine whether to change the color of the circle or to delete the shape.
	If msg = WM_LBUTTONUP Then
		MyWindow.changeColor = True
	End If
	If msg = WM_RBUTTONUP Then
		MyWindow.changeColor = False
	End If

	' Set up a callback to receive the hit test results enumeration.
	VisualTreeHelper.HitTest(MyWindow.myHwndSource.RootVisual, Nothing, New HitTestResultCallback(AddressOf CircleHitTestResult), New PointHitTestParameters(pt))

	' Perform actions on the hit test results list.
	If hitResultsList.Count > 0 Then
		ProcessHitTestResultsList()
	End If
End Sub

For more information on hit testing against visual objects, see Hit Testing in the Visual Layer.

See Also

HwndSource
Hit Test with Win32 Interoperation Sample
Hit Testing in the Visual Layer