How to set the client area (ClientRectangle) in a borderless form?

Question

I want to know if it's possible to set the client area of a borderless form. Say for example I define a form like so:

Code

public class MyForm : Form
{
    public MyForm()
    {
        this.FormBorderStyle = FormBorderStyle.None;
    }
}

Result

What I want to do is specify the client area, so that the form has a frame (like the standard windows frame, but custom drawn).

Result

Essentially, the blue area would become the non client area, and the gray area would remain as the client area.

I have tried to set the client area, but this just seems to resize the entire form, thus, is does not leave behind a "non-client" area

Is this possible?

Answer 1

This is possible, however I don't know how well this works with a Windows Form with the WindowStyle set to Borderless. Using PInvoke (Platform Invoke) Functions, you can remove window themes which will give you a very basic looking Windows Form. You can then use various PInvoke functions to manipulate the Non-client area of the windows form.

I recommend that you read through these topics. They're designed for Win32 Applications using C++, but PInvoke is the process of calling these native APIs using Managed Code (C#)

WM_NCCALCSIZE: https://msdn.microsoft.com/en-us/library/windows/desktop/ms632634(v=vs.85).aspx

WM_NCPAINT: https://msdn.microsoft.com/en-us/library/windows/desktop/dd145212(v=vs.85).aspx

GetDCEx: https://msdn.microsoft.com/en-us/library/windows/desktop/dd144873(v=vs.85).aspx

GetWindowDC: https://msdn.microsoft.com/en-us/library/windows/desktop/dd144947(v=vs.85).aspx

SetWindowTheme: https://msdn.microsoft.com/en-us/library/windows/desktop/bb759827(v=vs.85).aspx

This example is very very crude, but it provides basic functionality. I don't know how SetWindowTheme works on Windows 8 or 8.1, but in Windows 7, it gives windows the "classic" theme.

public partial class MyForm : Form
{
    //Window Messages
    public const uint WM_NCPAINT = 0x85;
    public const uint WM_NCCALCSIZE = 0x83;
    public const uint WM_NCHITTEST = 0x84;

    //GetDCEx Flags
    public const int DCX_WINDOW = 0x00000001;
    public const int DCX_CACHE = 0x00000002;
    public const int DCX_PARENTCLIP = 0x00000020;
    public const int DCX_CLIPSIBLINGS = 0x00000010;
    public const int DCX_CLIPCHILDREN = 0x00000008;
    public const int DCX_NORESETATTRS = 0x00000004;
    public const int DCX_LOCKWINDOWUPDATE = 0x00000400;
    public const int DCX_EXCLUDERGN = 0x00000040;
    public const int DCX_INTERSECTRGN = 0x00000080;
    public const int DCX_INTERSECTUPDATE = 0x00000200;
    public const int DCX_VALIDATE = 0x00200000;

    //RECT Structure
    [System.Runtime.InteropServices.StructLayout(System.Runtime.InteropServices.LayoutKind.Sequential)]
    public struct RECT
    {
        public int left, top, right, bottom;
    }

    //WINDOWPOS Structure
    [System.Runtime.InteropServices.StructLayout(System.Runtime.InteropServices.LayoutKind.Sequential)]
    public struct WINDOWPOS
    {
        public IntPtr hwnd;
        public IntPtr hwndinsertafter;
        public int x, y, cx, cy;
        public int flags;
    }

    //NCCALCSIZE_PARAMS Structure
    [System.Runtime.InteropServices.StructLayout(System.Runtime.InteropServices.LayoutKind.Sequential)]
    public struct NCCALCSIZE_PARAMS
    {
        public RECT rgrc0, rgrc1, rgrc2;
        public WINDOWPOS lppos;
    }

    //SetWindowTheme UXtheme Function
    [System.Runtime.InteropServices.DllImport("uxtheme.dll", ExactSpelling = true, CharSet = System.Runtime.InteropServices.CharSet.Unicode)]
    public static extern int SetWindowTheme(
        IntPtr hWnd,
        String pszSubAppName,
        String pszSubIdList);

    //GetWindowRect User32 Function
    [System.Runtime.InteropServices.DllImport("user32.dll", ExactSpelling = true)]
    [return: System.Runtime.InteropServices.MarshalAs(System.Runtime.InteropServices.UnmanagedType.Bool)]
    public static extern bool GetWindowRect(
        IntPtr hwnd,
        out  RECT lpRect
        );

    //GetWindowDC User32 Function
    [System.Runtime.InteropServices.DllImport("user32.dll", ExactSpelling = true)]
    public static extern IntPtr GetWindowDC(
        IntPtr hWnd
        );

    //GetDCEx User32 Function
    [System.Runtime.InteropServices.DllImport("user32.dll", ExactSpelling = true)]
    public static extern IntPtr GetDCEx(
        IntPtr hWnd,
        IntPtr hrgnClip,
        int flags
        );

    //Window Procedure Hook
    protected override void WndProc(ref Message m)
    {
        //Don't style window in designer...
        if (DesignMode)
            base.WndProc(ref m);

        //Handle Message
        switch ((uint)m.Msg)
        {
            case WM_NCCALCSIZE: WmNCCalcSize(ref m); break;
            case WM_NCPAINT: WmNCPaint(ref m); break;
            default: base.WndProc(ref m); break;
        }
    }

    //Handle Creation
    protected override void OnHandleCreated(EventArgs e)
    {
        //Base Procedure...
        base.OnHandleCreated(e);

        //Remove Theme
        SetWindowTheme(this.Handle, string.Empty, string.Empty);
    }

    //WM_NCCALCSIZE
    private void WmNCCalcSize(ref Message m)
    {
        //Get Window Rect
        RECT formRect = new RECT();
        GetWindowRect(m.HWnd, out formRect);

        //Check WPARAM
        if (m.WParam != IntPtr.Zero)    //TRUE
        {
            //When TRUE, LPARAM Points to a NCCALCSIZE_PARAMS structure
            var nccsp = (NCCALCSIZE_PARAMS)System.Runtime.InteropServices.Marshal.PtrToStructure(m.LParam, typeof(NCCALCSIZE_PARAMS));

            //We're adjusting the size of the client area here. Right now, the client area is the whole form.
            //Adding to the Top, Bottom, Left, and Right will size the client area.
            nccsp.rgrc0.top += 30;      //30-pixel top border
            nccsp.rgrc0.bottom -= 4;    //4-pixel bottom (resize) border
            nccsp.rgrc0.left += 4;      //4-pixel left (resize) border
            nccsp.rgrc0.right -= 4;     //4-pixel right (resize) border

            //Set the structure back into memory
            System.Runtime.InteropServices.Marshal.StructureToPtr(nccsp, m.LParam, true);
        }
        else    //FALSE
        {
            //When FALSE, LPARAM Points to a RECT structure
            var clnRect = (RECT)System.Runtime.InteropServices.Marshal.PtrToStructure(m.LParam, typeof(RECT));

            //Like before, we're adjusting the rectangle...
            //Adding to the Top, Bottom, Left, and Right will size the client area.
            clnRect.top += 30;      //30-pixel top border
            clnRect.bottom -= 4;    //4-pixel bottom (resize) border
            clnRect.left += 4;      //4-pixel left (resize) border
            clnRect.right -= 4;     //4-pixel right (resize) border

            //Set the structure back into memory
            System.Runtime.InteropServices.Marshal.StructureToPtr(clnRect, m.LParam, true);
        }

        //Return Zero
        m.Result = IntPtr.Zero;
    }

    //WM_NCPAINT
    private void WmNCPaint(ref Message m)
    {
        //Store HDC
        IntPtr HDC = IntPtr.Zero;
        Graphics gfx = null;

        //Check the WPARAM
        if(m.WParam == (IntPtr)1)
        {
            //For reasons unknown to me, the update region doesn't contain valid data and calling GetDCEx will do nothing.
            //So I call GetWindowDC and exclude the area using System.Drawing.Graphics instead.

            //Graphics Object from HDC
            HDC = GetWindowDC(m.HWnd);
            gfx = Graphics.FromHdc(HDC);

            //Exclude Client Area
            gfx.ExcludeClip(new Rectangle(4, 30, Width - 8, 34));  //Exclude Client Area (GetWindowDC grabs the WHOLE window's graphics handle)
        }
        else
        {
            //Graphics Object from HDC
            HDC = GetDCEx(m.HWnd, m.WParam, DCX_WINDOW | DCX_INTERSECTRGN);
            gfx = Graphics.FromHdc(HDC);
        }

        //Call Paint
        using (PaintEventArgs ncPaintArgs = new PaintEventArgs(gfx, new Rectangle(0, 0, Width, Height)))
            MyForm_NCPaint(this, ncPaintArgs);

        //Return Zero
        m.Result = IntPtr.Zero;
    }

    public MyForm()
    {
        InitializeComponent();
    }

    private void MyForm_NCPaint(object sender, PaintEventArgs e)
    {
        //Clear
        e.Graphics.Clear(Color.Green);
    }
}