How do I create a blurred-glass effect on a border-less Form?

Question

How do I draw a smooth blurred-glass effect on a border-less Form? I have tried the code listed on Image Processing for Dummies with C and GDI+ page but I\'m sure it\'s not what

Answer 1

I'll assume you are talking about Windows 7 / Vista, and you'd like to achieve the blurry transparent areas that some MS programs have in the same way. For the general case, you do need some image processing which I'm not going to cover.

For the case I mentioned above, you are not supposed to do this yourself - this is sort of re-inventing the wheel. Basically, you can use the window manager to achieve this effect (which is called aero glass) by using the methods described by this article: http://msdn.microsoft.com/en-us/magazine/cc163435.aspx

I currently have only a windows 8 machine (in which they cancelled this blurring and transparency by default) so I don't have a test environment to check this. I'll get to one later this week and set-up a sample code to do this,

Once you are using the desktop window manager, if you want just to blur the top part (like in your image), use DwmExtendFrameIntoClientArea to extend the frame (which is aero blurred by default) into your window. For a custom area, use DwmEnableBlurBehindWindow

So, in case this is really what you are looking for (solution for windows 7 / vista in the same way existing MS programs work), tell me and I'll update with code later. Otherwise, if you are looking for a general solution (not just windows vista / 7), tell me to save me the effort of coding this...

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EDIT: Given the fact that you chose to manually make the effect, here is some basic code to get you started

// Code was burrowed from:
//   http://stackoverflow.com/questions/19867402/how-can-i-use-enumwindows-to-find-windows-with-a-specific-caption-title
//   http://www.dotnetframework.org/default.aspx/4@0/4@0/DEVDIV_TFS/Dev10/Releases/RTMRel/ndp/fx/src/CommonUI/System/Drawing/NativeMethods@cs/1305376/NativeMethods@cs
//   http://stackoverflow.com/questions/7292757/how-to-get-screenshot-of-a-window-as-bitmap-object-in-c
//   http://stackoverflow.com/questions/798295/how-can-i-use-getnextwindow-in-c */

public static class WinAPI
{
   public delegate bool EnumWindowsProc(IntPtr hWnd, IntPtr lParam);

    [StructLayout(LayoutKind.Sequential)]
    public struct RECT
    {
        public int left;
        public int top;
        public int right;
        public int bottom;
    };

    public enum GW
    {
        GW_HWNDFIRST = 0,
        GW_HWNDLAST = 1,
        GW_HWNDNEXT = 2,
        GW_HWNDPREV = 3,
        GW_OWNER = 4,
        GW_CHILD = 5,
        GW_ENABLEDPOPUP = 6
    }

    [DllImport("User32.dll")]
    public static extern bool EnumWindows(EnumWindowsProc lpEnumFunc, IntPtr lParam);

    [DllImport("User32.dll", CharSet = CharSet.Unicode)]
    public static extern int GetWindowText(IntPtr hWnd, StringBuilder strText, int maxCount);

    [DllImport("User32.dll")]
    public static extern int GetWindowTextLength(IntPtr hWnd);

    [DllImport("User32.dll")]
    public static extern bool IsWindowVisible(IntPtr hWnd);

    [DllImport("User32.dll")]
    public static extern bool IsIconic(IntPtr hWnd);

    [DllImport("User32.dll")]
    public static extern bool GetClientRect(IntPtr hWnd, ref RECT lpRect);

    [DllImport("User32.dll")]
    public static extern bool GetWindowRect(IntPtr hWnd, ref RECT lpRect);

    [DllImport("User32.dll")]
    public static extern IntPtr GetDesktopWindow();

    [DllImport("User32.dll")]
    public static extern IntPtr GetTopWindow(IntPtr hWnd);

    public static IntPtr GetNextWindow(IntPtr hWnd, GW wCmd)
    {
        return GetWindow(hWnd, wCmd);
    }

    public static IntPtr GetWindow(IntPtr hWnd, GW wCmd)
    {
        return GetWindow(hWnd, (uint)wCmd);
    }

    [DllImport("User32.dll")]
    private static extern IntPtr GetWindow(IntPtr hWnd, uint wCmd);

    [DllImport("User32.dll")]
    public static extern bool PrintWindow(IntPtr hWnd, IntPtr hdcBlt, uint nFlags);

    [DllImport("User32.dll")]
    public static extern IntPtr GetDC(IntPtr hWnd);

    [DllImport("Gdi32.dll")]
    public static extern bool DeleteDC(IntPtr hdc);

    [DllImport("User32.dll")]
    public static extern IntPtr GetWindowDC(IntPtr hWnd);

    [DllImport("User32.dll")]
    public static extern int ReleaseDC(IntPtr hWnd, IntPtr hdc);

    [DllImport("User32.dll")]
    public static extern int GetWindowRgn(IntPtr hWnd, IntPtr hRgn);

    [DllImport("Gdi32.dll")]
    public static extern IntPtr CreateCompatibleDC(IntPtr hWnd);

    [DllImport("Gdi32.dll")]
    public static extern IntPtr CreateCompatibleBitmap(IntPtr hdc, int width, int height);

    [DllImport("Gdi32.dll")]
    public static extern IntPtr CreateBitmap(int width, int height, uint cPlanes, uint cBitsPerPel, IntPtr lpvBits);

    [DllImport("Gdi32.dll")]
    public static extern bool DeleteObject(IntPtr hGdiObj);

    [DllImport("Gdi32.dll")]
    public static extern bool SelectObject(IntPtr hdc, IntPtr hGdiObj);

    [DllImport("Gdi32.dll")]
    public static extern IntPtr CreateRectRgn(int nLeftRect, int nTopRect, int nRightRect, int nBottomRect);

    public static StringBuilder GetWindowText(IntPtr hWnd)
    {
        int length = GetWindowTextLength(hWnd);
        // Add another place to allow null terminator
        StringBuilder text = new StringBuilder(length + 1);
        GetWindowText(hWnd, text, length + 1);
        return text;    
    }

    public static bool IsWindowReallyVisible(IntPtr hWnd)
    {
        if (!IsWindowVisible(hWnd) || IsIconic(hWnd))
            return false;
        RECT area = new RECT();
        if (!GetWindowRect(hWnd, ref area))
            return true;
        if (area.left == area.right || area.bottom == area.top)
            return false;
        return true;
    }

    public enum RegionFlags
    {
        ERROR = 0,
        NULLREGION = 1,
        SIMPLEREGION = 2,
        COMPLEXREGION = 3,
    } 

}

public class ScreenShot
{
    public static List GetAllWindows(Func filter, Func stop)
    {
        List result = new List();

        WinAPI.EnumWindows((wnd, param) =>
        {
            bool relevant = filter(wnd);
            if (relevant)
                result.Add(wnd);
            bool shouldStop = stop(wnd);
            if (shouldStop)
                Console.WriteLine("Stop");
            return !shouldStop;
        }, IntPtr.Zero);

        return result;
    }

    public static IEnumerable GetWindowsByOrder(Func filter)
    {
        List skip = new List();
        List result = new List();
        IntPtr desktop = WinAPI.GetDesktopWindow();

        for (IntPtr wnd = WinAPI.GetTopWindow(IntPtr.Zero); wnd != IntPtr.Zero; wnd = WinAPI.GetNextWindow(wnd, WinAPI.GW.GW_HWNDNEXT))
        {
            if (result.Contains(wnd) || skip.Contains(wnd))
                break;
            else if (filter(wnd))
                result.Add(wnd);
            else
                skip.Add(wnd);
        }

        result.Add(desktop);
        return result;
    }

    public static Image GetScreenshot(IntPtr hWnd)
    {
        IntPtr hdcScreen = WinAPI.GetDC(hWnd);
        IntPtr hdc = WinAPI.CreateCompatibleDC(hdcScreen);
        WinAPI.RECT area = new WinAPI.RECT();

        WinAPI.GetWindowRect(hWnd, ref area);

        IntPtr hBitmap = WinAPI.CreateCompatibleBitmap(hdcScreen, area.right - area.left, area.bottom - area.top);
        WinAPI.SelectObject(hdc, hBitmap);

        WinAPI.PrintWindow(hWnd, hdc, 0);

        Image resultOpaque = Image.FromHbitmap(hBitmap);

        WinAPI.DeleteObject(hBitmap);
        WinAPI.DeleteDC(hdc);

        IntPtr hRegion = WinAPI.CreateRectRgn(0, 0, 0, 0);
        WinAPI.RegionFlags f = (WinAPI.RegionFlags) WinAPI.GetWindowRgn(hWnd, hRegion);
        Region region = Region.FromHrgn(hRegion);
        WinAPI.DeleteObject(hRegion);

        Bitmap result = new Bitmap(resultOpaque.Width, resultOpaque.Height, System.Drawing.Imaging.PixelFormat.Format32bppArgb);
        Graphics g = Graphics.FromImage(result);
        g.Clear(Color.Transparent);
        if (f != WinAPI.RegionFlags.ERROR)
            g.SetClip(region, System.Drawing.Drawing2D.CombineMode.Replace);
        if (f != WinAPI.RegionFlags.NULLREGION)
            g.DrawImageUnscaled(resultOpaque, 0, 0);

        g.Dispose();
        region.Dispose();
        resultOpaque.Dispose();

        return result;
    }

/* And now for the actual code of getting screenshots of windows */
var windows = ScreenShot.GetWindowsByOrder(this.WindowFilter).Intersect(ScreenShot.GetAllWindows(this.WindowFilter, (wnd) => false)).ToList();

int index = windows.IndexOf((IntPtr)this.Handle); /* Remove all the windows behind your windows */
if (index != -1)
    windows.RemoveRange(index, windows.Count - index + 1);

windows.Reverse();

/* Get the images of all the windows */
for (int i = 0; i < windows.Count; ++i )
{
    var window = windows[i];
    using (var img = ScreenShot.GetScreenshot(window))
    {
        // Get the actual position of the window
        // Draw it's image overlayed on the other windows 9have an accumulating image)
    }
}

Where does this still have bugs (on my testsuite in Windows 8.1)?

• I'm still having troubles with transparency - windows which are semi-transparent inside their clipping region still get painted black
• I have some unknown black windows (probably transparent) that still appear
• The taskbar doesn't paint correctly