WPF 制作支持点击穿透的高性能的透明背景异形窗口

    public class HwndTarget : CompositionTarget
    {
        /// <summary>
        /// The HwndTarget needs to see all windows messages so that
        /// it can appropriately react to them.
        /// </summary>
        internal IntPtr HandleMessage(WindowMessage msg, IntPtr wparam, IntPtr lparam)
        {
            switch (msg)
            {
                	// 忽略其他代码
                case WindowMessage.WM_STYLECHANGING:
                    unsafe
                    {
                        NativeMethods.STYLESTRUCT * styleStruct = (NativeMethods.STYLESTRUCT *) lparam;

                        if ((int)wparam == NativeMethods.GWL_EXSTYLE)
                        {
                        	// 这里的 UsesPerPixelOpacity 属性就是由 AllowsTransparency 决定的
                            if(UsesPerPixelOpacity)
                            {
                                // We need layered composition to accomplish per-pixel opacity.
                                //
                                styleStruct->styleNew |= NativeMethods.WS_EX_LAYERED;
                            }
                            else
                            {
                                // No properties that require layered composition exist.
                                // Make sure the layered bit is off.
                                //
                                // Note: this prevents an external program from making
                                // us system-layered (if we are a top-level window).
                                //
                                // If we are a child window, we still can't stop our
                                // parent from being made system-layered, and we will
                                // end up leaving visual artifacts on the screen under
                                // WindowsXP.
                                //
                                styleStruct->styleNew &= (~NativeMethods.WS_EX_LAYERED);
                            }
                        }
                    }

                    break;
             }
        }
    }

        private void PerformanceDesktopTransparentWindow_Loaded(object sender, RoutedEventArgs e)
        {
            ((HwndSource)PresentationSource.FromVisual(this)).AddHook((IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled) =>
            {
                //想要让窗口透明穿透鼠标和触摸等，需要同时设置 WS_EX_LAYERED 和 WS_EX_TRANSPARENT 样式，
                //确保窗口始终有 WS_EX_LAYERED 这个样式，并在开启穿透时设置 WS_EX_TRANSPARENT 样式
                //但是WPF窗口在未设置 AllowsTransparency = true 时，会自动去掉 WS_EX_LAYERED 样式（在 HwndTarget 类中)，
                //如果设置了 AllowsTransparency = true 将使用WPF内置的低性能的透明实现，
                //所以这里通过 Hook 的方式，在不使用WPF内置的透明实现的情况下，强行保证这个样式存在。
                if (msg == (int)Win32.WM.STYLECHANGING && (long)wParam == (long)Win32.GetWindowLongFields.GWL_EXSTYLE)
                {
                    var styleStruct = (STYLESTRUCT)Marshal.PtrToStructure(lParam, typeof(STYLESTRUCT));
                    styleStruct.styleNew |= (int)Win32.ExtendedWindowStyles.WS_EX_LAYERED;
                    Marshal.StructureToPtr(styleStruct, lParam, false);
                    handled = true;
                }
                return IntPtr.Zero;
            });
        }

        /// <summary>
        /// 设置点击穿透到后面透明的窗口
        /// </summary>
        public void SetTransparentHitThrough()
        {
            if (_dwmEnabled)
            {
                Win32.User32.SetWindowLongPtr(_hwnd, Win32.GetWindowLongFields.GWL_EXSTYLE,
                    (IntPtr)(int)((long)Win32.User32.GetWindowLongPtr(_hwnd, Win32.GetWindowLongFields.GWL_EXSTYLE) | (long)Win32.ExtendedWindowStyles.WS_EX_TRANSPARENT));
            }
            else
            {
                Background = Brushes.Transparent;
            }
        }

        /// <summary>
        /// 设置点击命中，不会穿透到后面的窗口
        /// </summary>
        public void SetTransparentNotHitThrough()
        {
            if (_dwmEnabled)
            {
                Win32.User32.SetWindowLongPtr(_hwnd, Win32.GetWindowLongFields.GWL_EXSTYLE,
                    (IntPtr)(int)((long)Win32.User32.GetWindowLongPtr(_hwnd, Win32.GetWindowLongFields.GWL_EXSTYLE) & ~(long)Win32.ExtendedWindowStyles.WS_EX_TRANSPARENT));
            }
            else
            {
                Background = BrushCreator.GetOrCreate("#0100000");
            }
        }

        public static class Dwmapi
        {
            public const string LibraryName = "Dwmapi.dll";

            [DllImport(LibraryName, ExactSpelling = true, PreserveSig = false)]
            [return: MarshalAs(UnmanagedType.Bool)]
            public static extern bool DwmIsCompositionEnabled();
        }