用于 WPF 无边框窗口的 DropShadow [英] DropShadow for WPF Borderless Window

问题描述

我有一个 WPF 窗口，WindowStyle 设置为 none.有什么方法可以强制这个窗口投下阴影(就像当 WindowStyle 不是 none 时你得到的那个)?我不想将 AllowTransparency 设置为 true，因为它会影响性能.而且我也不想禁用硬件渲染(我在某处读到过禁用透明度效果更好).

I have a WPF Window with WindowStyle set to none. Is there some way I can force this window to drop a shadow (like the one you get when WindowStyle is not none)? I don't want to set AllowTransparency to true, because it affects the performance. And I also don't want to disable hardware rendering (I read somewhere that transparency performs better with it disabled).

推荐答案

我写了一个小工具类，它能够完全按照你的要求做:在无边框的 Window 上放置一个标准的阴影，但是将 AllowsTransparency 设置为 false.

I have written a little utility class that is able to do exactly what you want: drop a standard shadow over a borderless Window but having AllowsTransparency set to false.

您只需要调用DropShadowToWindow(Window window) 方法.最好在窗口的构造函数的 InitializeComponent() 之后进行此调用，但即使在显示窗口之后调用它也能正常工作.

You just have to call the DropShadowToWindow(Window window) method. It is preferred that you make this call just after the window's constructor's InitializeComponent(), but it will work even if you call it after the window is shown.

using System;
using System.Drawing.Printing;
using System.Runtime.InteropServices;
using System.Windows;
using System.Windows.Interop;

public static class DwmDropShadow
{
    [DllImport("dwmapi.dll", PreserveSig = true)]
    private static extern int DwmSetWindowAttribute(IntPtr hwnd, int attr, ref int attrValue, int attrSize);

    [DllImport("dwmapi.dll")]
    private static extern int DwmExtendFrameIntoClientArea(IntPtr hWnd, ref Margins pMarInset);

    /// <summary>
    /// Drops a standard shadow to a WPF Window, even if the window is borderless. Only works with DWM (Windows Vista or newer).
    /// This method is much more efficient than setting AllowsTransparency to true and using the DropShadow effect,
    /// as AllowsTransparency involves a huge performance issue (hardware acceleration is turned off for all the window).
    /// </summary>
    /// <param name="window">Window to which the shadow will be applied</param>
    public static void DropShadowToWindow(Window window)
    {
        if (!DropShadow(window))
        {
            window.SourceInitialized += new EventHandler(window_SourceInitialized);
        }
    }

    private static void window_SourceInitialized(object sender, EventArgs e)
    {
        Window window = (Window)sender;

        DropShadow(window);

        window.SourceInitialized -= new EventHandler(window_SourceInitialized);
    }

    /// <summary>
    /// The actual method that makes API calls to drop the shadow to the window
    /// </summary>
    /// <param name="window">Window to which the shadow will be applied</param>
    /// <returns>True if the method succeeded, false if not</returns>
    private static bool DropShadow(Window window)
    {
        try
        {
            WindowInteropHelper helper = new WindowInteropHelper(window);
            int val = 2;
            int ret1 = DwmSetWindowAttribute(helper.Handle, 2, ref val, 4);

            if (ret1 == 0)
            {
                Margins m = new Margins { Bottom = 0, Left = 0, Right = 0, Top = 0 };
                int ret2 = DwmExtendFrameIntoClientArea(helper.Handle, ref m);
                return ret2 == 0;
            }
            else
            {
                return false;
            }
        }
        catch (Exception ex)
        {
            // Probably dwmapi.dll not found (incompatible OS)
            return false;
        }
    }
}

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