Question

I have a C# .NET WinForm app which draws to the non-client area. Everything works fine and the drawing happens as expected with the exception of when the form loads.

I catch the WM_NCPAINT fine but when i try to get the DC using GetDCEx it always returns null until the form has been displayed which is perfectly logical but that means that the non-client area isnt painted again until the window is resized which means that when the form is first loaded or restored from a minimized state the NC area isnt redrawn and remains white.

This seems to be unique to Windows 7.

So how do I draw to the NC area in this situation?

EDIT: I should add that I dont care about Aero glass and my form disables it entirely.

Answer 1

Instead of GetDCEx, I use GetWindowDC. Below is the code I use, and I haven’t had an issue with Windows 7. As Hans commented, the best way is to set the FormBorderStyle to None, but then I like to put in my own borders using this code from csharptest.net

Imports System.Runtime.InteropServices

Public Class NCForm    
  Inherits Form

  Public Sub New()
    Me.FormBorderStyle = FormBorderStyle.None
  End Sub

  Protected Overrides Sub WndProc(ByRef m As Message)
    MyBase.WndProc(m)

    If m.Msg = Win32.WM_NCCALCSIZE Then        
      If m.WParam <> IntPtr.Zero Then
        Dim tmpResize As Win32.NCCALCSIZE_PARAMS = Marshal.PtrToStructure(m.LParam, GetType(Win32.NCCALCSIZE_PARAMS))
        With tmpResize.rcNewWindow
          .Left += 2
          .Top += 2
          .Right -= 2
          .Bottom -= 2
        End With
        Marshal.StructureToPtr(tmpResize, m.LParam, False)
      Else
        Dim tmpResize As Win32.RECT = Marshal.PtrToStructure(m.LParam, GetType(Win32.RECT))
        With tmpResize
          .Left += 2
          .Top += 2
          .Right -= 2
          .Bottom -= 2
        End With
        Marshal.StructureToPtr(tmpResize, m.LParam, False)
      End If
      m.Result = New IntPtr(1)

    ElseIf m.Msg = Win32.WM_NCPAINT Then
      Dim tmpDC as IntPtr = Win32.GetWindowDC(m.HWnd)
      Using tmpG As Graphics = Graphics.FromHdc(tmpDC)
        tmpG.DrawRectangle(Pens.Red, New Rectangle(0, 0, Me.Width - 1, Me.Height - 1))
        tmpG.DrawRectangle(SystemPens.Window, New Rectangle(1, 1, Me.Width-3, Me.Height - 3))
      End Using
      Win32.ReleaseDC(m.HWnd, tmpDC)
    End If
  End Sub

Of course, once you do this, then you have to handle any resize, min-max, closing functionality yourself.