c# - 如何在 Windows 窗体中创建半透明或模糊的背景色

Question

我正在创建一个速度计来测量我的互联网速度并保持在每个应用程序的顶部，然后我如何使它的背景半透明或像这样模糊。

Answer 1

一个应用了模糊效果的 WinForms Form，使用:
Windows 7 ⇒ DwmEnableBlurBehindWindow() DWM功能。
Windows 10/11 ⇒ SetWindowCompositionAttribute() User32 函数(未记录)

如何应用背后模糊效果:
Windows 7:
窗口需要使用 DwmSetWindowAttribute() 注册渲染策略, 设置 DWMWINDOWATTRIBUTE枚举器到 NCRenderingPolicy 并启用它，设置 DWMNCRENDERINGPOLICY Enabled 的枚举数。
您可能还想重写 Form 的类 WndProc；当WM_DWMCOMPOSITIONCHANGED收到消息(通知 Aero 组合状态)，以验证 DWM 组合是否已启用。

在显示窗口界面之前，调用DwmEnableBlurBehindWindow() , 设置它的 DWM_BLURBEHIND将相关字段(dwFlags 和fEnable)结构化为1。
在这里，我从 Form 的构造函数中调用它。

Windows 10 和 Windows 11:
此代码使用尚未记录的 SetWindowCompositionAttribute() 函数。
User32函数只需要使用一个内部结构，这里叫做WinCompositionAttrData，其中Attribute 成员设置为 DWMWINDOWATTRIBUTE.AccentPolicy 并且 Data 成员设置为一个指针内部结构，这里称为 AccentPolicy，其中 AccentState 成员设置为 DWMACCENTSTATE。 ACCENT_ENABLE_BLURBEHIND

DWM 组合始终处于启用状态。无需验证它或覆盖 WndProc 来处理 DWM 组合更改。

在代码中更清晰:
(请注意，如果表单具有白色 背景色，则BlurBehind 效果不起作用)

See this other question关于 DwmExtendFrameIntoClientArea() 实现。

public partial class frmBlurBehind : Form
{
    public frmBlurBehind()
    {
        InitializeComponent();

        // Remove the border if this is meant to be a border-less Form
        // FormBorderStyle = FormBorderStyle.None;

        if (IsDWMCompositionEnabled()) {
            if (Environment.OSVersion.Version.Major > 6) {
                Dwm.Windows10EnableBlurBehind(Handle);
            }
            else {
                Dwm.WindowEnableBlurBehind(Handle);
            }
            // Set Drop shadow of a border-less Form
            if (FormBorderStyle == FormBorderStyle.None) {
                Dwm.WindowBorderlessDropShadow(Handle, 2);
            }
        }
    }

    private bool IsDWMCompositionEnabled() => 
        Environment.OSVersion.Version.Major >= 6 && Dwm.IsCompositionEnabled();

    // Eventually, if this is a border-less Form, reapply the attribute if DWM Composition changes
    protected override void WndProc(ref Message m)
    {
        base.WndProc(ref m);
        switch (m.Msg) {
            case Dwm.WM_DWMCOMPOSITIONCHANGED:
                if (IsDWMCompositionEnabled()) {
                    Dwm.DWMNCRENDERINGPOLICY policy = Dwm.DWMNCRENDERINGPOLICY.Enabled;
                    Dwm.WindowSetAttribute(Handle, Dwm.DWMWINDOWATTRIBUTE.NCRenderingPolicy, (int)policy);
                    Dwm.WindowBorderlessDropShadow(Handle, 2);
                    m.Result = IntPtr.Zero;
                }
                break;
            default:
                break;
        }
    }
}

---

Dwm 类包含上面使用的所有互操作函数和结构，以及一些可能在此上下文中有用的其他方法

[SuppressUnmanagedCodeSecurity]
public class Dwm {
    public const int WM_DWMCOMPOSITIONCHANGED = 0x031E;

    public struct MARGINS {
        public int leftWidth;
        public int rightWidth;
        public int topHeight;
        public int bottomHeight;

        public MARGINS(int LeftWidth, int RightWidth, int TopHeight, int BottomHeight)
        {
            leftWidth = LeftWidth;
            rightWidth = RightWidth;
            topHeight = TopHeight;
            bottomHeight = BottomHeight;
        }

        public void NoMargins()
        {
            leftWidth = 0;
            rightWidth = 0;
            topHeight = 0;
            bottomHeight = 0;
        }

        public void SheetOfGlass()
        {
            leftWidth = -1;
            rightWidth = -1;
            topHeight = -1;
            bottomHeight = -1;
        }
    }

    [Flags]
    public enum DWM_BB {
        Enable = 1,
        BlurRegion = 2,
        TransitionOnMaximized = 4
    }

    // https://learn.microsoft.com/en-us/windows/win32/api/dwmapi/ne-dwmapi-dwmwindowattribute
    public enum DWMWINDOWATTRIBUTE : uint {
        NCRenderingEnabled = 1,       //Get atttribute
        NCRenderingPolicy,            //Enable or disable non-client rendering
        TransitionsForceDisabled,
        AllowNCPaint,
        CaptionButtonBounds,          //Get atttribute
        NonClientRtlLayout,
        ForceIconicRepresentation,
        Flip3DPolicy,
        ExtendedFrameBounds,          //Get atttribute
        HasIconicBitmap,
        DisallowPeek,
        ExcludedFromPeek,
        Cloak,
        Cloaked,                      //Get atttribute. Returns a DWMCLOACKEDREASON
        FreezeRepresentation,
        PassiveUpdateMode,
        UseHostBackDropBrush,
        AccentPolicy = 19,            // Win 10 (undocumented)
        ImmersiveDarkMode = 20,       // Win 11 22000
        WindowCornerPreference = 33,  // Win 11 22000
        BorderColor,                  // Win 11 22000
        CaptionColor,                 // Win 11 22000
        TextColor,                    // Win 11 22000
        VisibleFrameBorderThickness,  // Win 11 22000
        SystemBackdropType            // Win 11 22621
    }

    public enum DWMCLOACKEDREASON : uint {
        DWM_CLOAKED_APP = 0x0000001,       //cloaked by its owner application.
        DWM_CLOAKED_SHELL = 0x0000002,     //cloaked by the Shell.
        DWM_CLOAKED_INHERITED = 0x0000004  //inherited from its owner window.
    }

    public enum DWMNCRENDERINGPOLICY : uint {
        UseWindowStyle, // Enable/disable non-client rendering based on window style
        Disabled,       // Disabled non-client rendering; window style is ignored
        Enabled,        // Enabled non-client rendering; window style is ignored
    };

    public enum DWMACCENTSTATE {
        ACCENT_DISABLED = 0,
        ACCENT_ENABLE_GRADIENT = 1,
        ACCENT_ENABLE_TRANSPARENTGRADIENT = 2,
        ACCENT_ENABLE_BLURBEHIND = 3,
        ACCENT_INVALID_STATE = 4
    }

    [Flags]
    public enum CompositionAction : uint {
        DWM_EC_DISABLECOMPOSITION = 0,
        DWM_EC_ENABLECOMPOSITION = 1
    }

    // Values designating how Flip3D treats a given window.
    enum DWMFLIP3DWINDOWPOLICY : uint {
        Default,        // Hide or include the window in Flip3D based on window style and visibility.
        ExcludeBelow,   // Display the window under Flip3D and disabled.
        ExcludeAbove,   // Display the window above Flip3D and enabled.
    };

    public enum ThumbProperties_dwFlags : uint {
        RectDestination = 0x00000001,
        RectSource = 0x00000002,
        Opacity = 0x00000004,
        Visible = 0x00000008,
        SourceClientAreaOnly = 0x00000010
    }


    [StructLayout(LayoutKind.Sequential)]
    public struct AccentPolicy {
        public DWMACCENTSTATE AccentState;
        public int AccentFlags;
        public int GradientColor;
        public int AnimationId;

        public AccentPolicy(DWMACCENTSTATE accentState, int accentFlags, int gradientColor, int animationId)
        {
            AccentState = accentState;
            AccentFlags = accentFlags;
            GradientColor = gradientColor;
            AnimationId = animationId;
        }
    }

    [StructLayout(LayoutKind.Sequential)]
    public struct DWM_BLURBEHIND {
        public DWM_BB dwFlags;
        public int fEnable;
        public IntPtr hRgnBlur;
        public int fTransitionOnMaximized;

        public DWM_BLURBEHIND(bool enabled)
        {
            dwFlags = DWM_BB.Enable;
            fEnable = (enabled) ? 1 : 0;
            hRgnBlur = IntPtr.Zero;
            fTransitionOnMaximized = 0;
        }

        public Region Region => Region.FromHrgn(hRgnBlur);

        public bool TransitionOnMaximized {
            get => fTransitionOnMaximized > 0;
            set {
                fTransitionOnMaximized = (value) ? 1 : 0;
                dwFlags |= DWM_BB.TransitionOnMaximized;
            }
        }

        public void SetRegion(Graphics graphics, Region region)
        {
            hRgnBlur = region.GetHrgn(graphics);
            dwFlags |= DWM_BB.BlurRegion;
        }
    }

    [StructLayout(LayoutKind.Sequential)]
    public struct WinCompositionAttrData {
        public DWMWINDOWATTRIBUTE Attribute;
        public IntPtr Data;  //Will point to an AccentPolicy struct, where Attribute will be DWMWINDOWATTRIBUTE.AccentPolicy
        public int SizeOfData;

        public WinCompositionAttrData(DWMWINDOWATTRIBUTE attribute, IntPtr data, int sizeOfData)
        {
            Attribute = attribute;
            Data = data;
            SizeOfData = sizeOfData;
        }
    }

    private static int GetBlurBehindPolicyAccentFlags()
    {
        int drawLeftBorder = 20;
        int drawTopBorder = 40;
        int drawRightBorder = 80;
        int drawBottomBorder = 100;
        return (drawLeftBorder | drawTopBorder | drawRightBorder | drawBottomBorder);
    }

    //https://msdn.microsoft.com/en-us/library/windows/desktop/aa969508(v=vs.85).aspx
    [DllImport("dwmapi.dll")]
    internal static extern int DwmEnableBlurBehindWindow(IntPtr hwnd, ref DWM_BLURBEHIND blurBehind);

    [DllImport("dwmapi.dll", PreserveSig = false)]
    public static extern void DwmEnableComposition(CompositionAction uCompositionAction);

    //https://msdn.microsoft.com/it-it/library/windows/desktop/aa969512(v=vs.85).aspx
    [DllImport("dwmapi.dll")]
    internal static extern int DwmExtendFrameIntoClientArea(IntPtr hWnd, ref MARGINS pMarInset);

    //https://msdn.microsoft.com/en-us/library/windows/desktop/aa969515(v=vs.85).aspx
    [DllImport("dwmapi.dll")]
    internal static extern int DwmGetWindowAttribute(IntPtr hwnd, DWMWINDOWATTRIBUTE attr, ref int attrValue, int attrSize);

    //https://msdn.microsoft.com/en-us/library/windows/desktop/aa969524(v=vs.85).aspx
    [DllImport("dwmapi.dll")]
    internal static extern int DwmSetWindowAttribute(IntPtr hwnd, DWMWINDOWATTRIBUTE attr, ref int attrValue, int attrSize);

    [DllImport("User32.dll", SetLastError = true)]
    internal static extern int SetWindowCompositionAttribute(IntPtr hwnd, ref WinCompositionAttrData data);

    [DllImport("dwmapi.dll")]
    internal static extern int DwmIsCompositionEnabled(ref int pfEnabled);

    public static bool IsCompositionEnabled()
    {
        int pfEnabled = 0;
        int result = DwmIsCompositionEnabled(ref pfEnabled);
        return (pfEnabled == 1) ? true : false;
    }

    public static bool IsNonClientRenderingEnabled(IntPtr hWnd)
    {
        int gwaEnabled = 0;
        int result = DwmGetWindowAttribute(hWnd, DWMWINDOWATTRIBUTE.NCRenderingEnabled, ref gwaEnabled, sizeof(int));
        return gwaEnabled == 1;
    }

    public static bool WindowSetAttribute(IntPtr hWnd, DWMWINDOWATTRIBUTE attribute, int attributeValue)
    {
        int result = DwmSetWindowAttribute(hWnd, attribute, ref attributeValue, sizeof(int));
        return (result == 0);
    }

    public static void Windows10EnableBlurBehind(IntPtr hWnd)
    {
        DWMNCRENDERINGPOLICY policy = DWMNCRENDERINGPOLICY.Enabled;
        WindowSetAttribute(hWnd, DWMWINDOWATTRIBUTE.NCRenderingPolicy, (int)policy);

        AccentPolicy accPolicy = new AccentPolicy() {
            AccentState = DWMACCENTSTATE.ACCENT_ENABLE_BLURBEHIND,
        };

        int accentSize = Marshal.SizeOf(accPolicy);
        IntPtr accentPtr = Marshal.AllocHGlobal(accentSize);
        Marshal.StructureToPtr(accPolicy, accentPtr, false);
        var data = new WinCompositionAttrData(DWMWINDOWATTRIBUTE.AccentPolicy, accentPtr, accentSize);

        SetWindowCompositionAttribute(hWnd, ref data);
        Marshal.FreeHGlobal(accentPtr);
    }

    public static bool WindowEnableBlurBehind(IntPtr hWnd)
    {
        DWMNCRENDERINGPOLICY policy = DWMNCRENDERINGPOLICY.Enabled;
        WindowSetAttribute(hWnd, DWMWINDOWATTRIBUTE.NCRenderingPolicy, (int)policy);

        DWM_BLURBEHIND dwm_BB = new DWM_BLURBEHIND(true);
        int result = DwmEnableBlurBehindWindow(hWnd, ref dwm_BB);
        return result == 0;
    }

    public static bool WindowExtendIntoClientArea(IntPtr hWnd, MARGINS margins)
    {
        // Extend frame on the bottom of client area
        int result = DwmExtendFrameIntoClientArea(hWnd, ref margins);
        return result == 0;
    }

    public static bool WindowBorderlessDropShadow(IntPtr hWnd, int shadowSize)
    {
        MARGINS margins = new MARGINS(0, shadowSize, 0, shadowSize);
        int result = DwmExtendFrameIntoClientArea(hWnd, ref margins);
        return result == 0;
    }

    public static bool WindowSheetOfGlass(IntPtr hWnd)
    {
        MARGINS margins = new MARGINS();

        //Margins set to All:-1 - Sheet Of Glass effect
        margins.SheetOfGlass();
        int result = DwmExtendFrameIntoClientArea(hWnd, ref margins);
        return result == 0;
    }

    public static bool WindowDisableRendering(IntPtr hWnd)
    {
        int ncrp = (int)DWMNCRENDERINGPOLICY.Disabled;
        // Disable non-client area rendering on the window.
        int result = DwmSetWindowAttribute(hWnd, DWMWINDOWATTRIBUTE.NCRenderingPolicy, ref ncrp, sizeof(int));
        return result == 0;
    }
}   //DWM

这是将 Form.BackColor 设置为 MidnightBlue 的示例结果:

                Window Selected                              Windows Unselected

上面有一些控件: