Code:
/ 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / wpf / src / Core / CSharp / System / Windows / Media / MediaContextNotificationWindow.cs / 1407647 / MediaContextNotificationWindow.cs
//------------------------------------------------------------------------------ // //// Copyright (c) Microsoft Corporation. All rights reserved. // // // Description: // A wrapper for a top-level hidden window that is used to process // messages broadcasted to top-level windows only (such as DWM's // WM_DWMCOMPOSITIONCHANGED). If the WPF application doesn't have // a top-level window (as it is the case for XBAP applications), // such messages would have been ignored. // //----------------------------------------------------------------------------- using System; using System.Windows.Threading; using System.Collections; using System.Diagnostics; using System.Runtime.InteropServices; using System.Windows.Media.Animation; using System.Windows.Media.Composition; using Microsoft.Win32; using Microsoft.Internal; using MS.Internal; using MS.Internal.Interop; using MS.Win32; using System.Security; using System.Security.Permissions; using SR=MS.Internal.PresentationCore.SR; using SRID=MS.Internal.PresentationCore.SRID; namespace System.Windows.Media { ////// The MediaContextNotificationWindow class provides its owner /// MediaContext with the ability to receive and forward window /// messages broadcasted to top-level windows. /// internal class MediaContextNotificationWindow : IDisposable { ////// Initializes static variables for this class. /// ////// Critical - Sets the SecurityCritical static variables holding the message ids; calls RegisterWindowMessage. /// TreatAsSafe - The message ids are not exposed; no external parameters are taken in. /// [SecurityCritical, SecurityTreatAsSafe] static MediaContextNotificationWindow() { s_channelNotifyMessage = UnsafeNativeMethods.RegisterWindowMessage("MilChannelNotify"); s_dwmRedirectionEnvironmentChanged = UnsafeNativeMethods.RegisterWindowMessage("DwmRedirectionEnvironmentChangedHint"); } //+--------------------------------------------------------------------- // // Internal Methods // //--------------------------------------------------------------------- #region Internal Methods ////// Sets the owner MediaContext and creates the notification window. /// ////// Critical - Creates an HwndWrapper and adds a hook. /// TreatAsSafe: Critical data is not exposed. /// [SecurityCritical, SecurityTreatAsSafe] internal MediaContextNotificationWindow(MediaContext ownerMediaContext) { // Remember the pointer to the owner MediaContext that we'll forward the broadcasts to. _ownerMediaContext = ownerMediaContext; // Create a top-level, invisible window so we can get the WM_DWMCOMPOSITIONCHANGED // and other DWM notifications that are broadcasted to top-level windows only. HwndWrapper hwndNotification; hwndNotification = new HwndWrapper(0, NativeMethods.WS_POPUP, 0, 0, 0, 0, 0, "MediaContextNotificationWindow", IntPtr.Zero, null); _hwndNotificationHook = new HwndWrapperHook(MessageFilter); _hwndNotification = new SecurityCriticalDataClass(hwndNotification); _hwndNotification.Value.AddHook(_hwndNotificationHook); _isDisposed = false; // // On Vista, we need to know when the Magnifier goes on and off // in order to switch to and from software rendering because the // Vista Magnifier cannot magnify D3D content. To receive the // window message informing us of this, we must tell the DWM // we are MIL content. // // The Win7 Magnifier can magnify D3D content so it's not an // issue there. In fact, Win7 doesn't even send the WM. // // If the DWM is not running, this call will result in NoOp. // ChangeWindowMessageFilter(s_dwmRedirectionEnvironmentChanged, 1 /* MSGFLT_ADD */); MS.Internal.HRESULT.Check(MilContent_AttachToHwnd(_hwndNotification.Value.Handle)); } /// /// Critical - Calls dispose on the critical hwnd wrapper. /// TreatAsSafe: It is safe to dispose the wrapper /// [SecurityCritical, SecurityTreatAsSafe] public void Dispose() { if (!_isDisposed) { // // If DWM is not running, this call will result in NoOp. // MS.Internal.HRESULT.Check(MilContent_DetachFromHwnd(_hwndNotification.Value.Handle)); _hwndNotification.Value.Dispose(); _hwndNotificationHook = null; _hwndNotification = null; _ownerMediaContext = null; _isDisposed = true; GC.SuppressFinalize(this); } } #endregion Internal Methods //+---------------------------------------------------------------------- // // Private Methods // //--------------------------------------------------------------------- #region Private Methods ////// Tells a channel to send notifications to a particular target's window. /// /// /// The channel from which we want notifications. /// ////// Critical - Calls a critical channel method. /// TreatAsSafe - We are associated with the window handle that we /// are passing to the channel, so somebody already /// decided that it's OK for us to interact with that /// window. We also registered a window message so /// that we can avoid collisions with other messages. /// [SecurityCritical, SecurityTreatAsSafe] internal void SetAsChannelNotificationWindow() { if (_isDisposed) { throw new ObjectDisposedException("MediaContextNotificationWindow"); } _ownerMediaContext.Channel.SetNotificationWindow(_hwndNotification.Value.Handle, s_channelNotifyMessage); } ////// If any of the interesting broadcast messages is seen, forward them to the owner MediaContext. /// ////// Critical: Calls into unmanaged code, uses sensitive HWND data /// TreatAsSafe: No sensitive information is disclosed. It's safe to "attach" the window to the DWM. /// [SecurityCritical, SecurityTreatAsSafe] private IntPtr MessageFilter(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled) { if (_isDisposed) { throw new ObjectDisposedException("MediaContextNotificationWindow"); } WindowMessage message = (WindowMessage)msg; Debug.Assert(_ownerMediaContext != null); if (message == WindowMessage.WM_DWMCOMPOSITIONCHANGED) { // // We need to register as MIL content to receive the Vista Magnifier messages // (see comments in ctor). // // We're going to attempt to attach to DWM every time the desktop composition // state changes to ensure that we properly handle DWM crashing/restarting/etc. // MS.Internal.HRESULT.Check(MilContent_AttachToHwnd(_hwndNotification.Value.Handle)); } else if (message == s_channelNotifyMessage) { _ownerMediaContext.NotifyChannelMessage(); } else if (message == s_dwmRedirectionEnvironmentChanged) { MediaSystem.NotifyRedirectionEnvironmentChanged(); } return IntPtr.Zero; } ////// Critical: This code causes unmanaged code elevation /// [SecurityCritical, SuppressUnmanagedCodeSecurity] [DllImport(DllImport.MilCore)] private static extern int MilContent_AttachToHwnd( IntPtr hwnd ); ////// Critical: This code causes unmanaged code elevation /// [SecurityCritical, SuppressUnmanagedCodeSecurity] [DllImport(DllImport.MilCore)] private static extern int MilContent_DetachFromHwnd( IntPtr hwnd ); ////// Allow lower integrity applications to send specified window messages /// in case we are elevated. Failure is non-fatal and on down-level /// platforms this call will result in a no-op. /// ////// Critical -- Calls unsafe native methods GetModuleHandle and GetProcAddress. /// Manually elevates unmanaged code permissions to pinvoke through /// a function pointer. /// [SecurityCritical] private void ChangeWindowMessageFilter(WindowMessage message, uint flag) { // Find the address of ChangeWindowMessageFilter in user32.dll. IntPtr user32Module = UnsafeNativeMethods.GetModuleHandle("user32.dll"); // Get the address of the function. If this fails it means the OS // doesn't support this function, in which case we don't // need to do anything further. IntPtr functionAddress = UnsafeNativeMethods.GetProcAddressNoThrow( new HandleRef(null, user32Module), "ChangeWindowMessageFilter"); if (functionAddress != IntPtr.Zero) { // Convert the function pointer into a callable delegate and then call it ChangeWindowMessageFilterNative function = Marshal.GetDelegateForFunctionPointer( functionAddress, typeof(ChangeWindowMessageFilterNative)) as ChangeWindowMessageFilterNative; // In order to call the function we need unmanaged code access, // because the function is native code. (new SecurityPermission(SecurityPermissionFlag.UnmanagedCode)).Assert(); try { function(message, flag); } finally { SecurityPermission.RevertAssert(); } } } ////// Prototype for user32's ChangeWindowMessageFilter function, which we load dynamically on Vista+. /// [UnmanagedFunctionPointer(CallingConvention.Winapi)] private delegate void ChangeWindowMessageFilterNative(WindowMessage message, uint flag); #endregion Private Methods //+---------------------------------------------------------------------- // // Private Fields // //---------------------------------------------------------------------- #region Private Fields private bool _isDisposed; // The owner MediaContext private MediaContext _ownerMediaContext; // A top-level hidden window. private SecurityCriticalDataClass_hwndNotification; // The message filter hook for the top-level hidden window. private HwndWrapperHook _hwndNotificationHook; // The window message used to announce a channel notification. private static WindowMessage s_channelNotifyMessage; // We receive this when the Vista Magnifier goes on/off private static WindowMessage s_dwmRedirectionEnvironmentChanged; #endregion Private Fields } } // File provided for Reference Use Only by Microsoft Corporation (c) 2007.
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