Need ScrollWindowEx Calling Help

[Scott Gunn]

Hello

I'm trying to scroll a region of graphics, the best way I can see is to use
the ScrollWindowEx API because it is designed for doing this

However it doesn't work correctly, Why?

Here is my code:

Public Class Win32
<DllImport("use r32.dll")> _
Public Shared Function ScrollWindowEx( ByVal hWnd As IntPtr, ByVal dx As
Integer, ByVal dy As Integer, <MarshalAs(Unma nagedType.Struc t)> ByVal
prcScroll As Rectangle, <MarshalAs(Unma nagedType.Struc t)> ByVal prcClip As
Rectangle, ByVal hrgnUpdate As IntPtr,
<System.Runtime .InteropService s.Out(), MarshalAs(Unman agedType.Struct )>
ByRef prcUpdate As Rectangle, <MarshalAs(Unma nagedType.U4)> ByVal flags As
Integer) As Integer
End Function
End Class

Private Sub barScroll_Scrol l(ByVal sender As System.Object, ByVal e As
System.Windows. Forms.ScrollEve ntArgs) Handles barScroll.Scrol l
Dim rt As Rectangle = New Rectangle
Dim rtout As Rectangle = New Rectangle(0, 0, 10, 10)
Dim rtin As Rectangle = New Rectangle(20, 20, 100, 100)
Dim rr As Integer = Win32.ScrollWin dowEx(Handle, 0, 10, rtin, rt,
IntPtr.Zero, rtout, 0)
End Sub

rr is the return from the ScrollWindowEx function and this returns 0 but
nothing happens on the screen.

err.LastDllErro r returns 993 which means Invalid access to memory location.

If I change this:
Dim rr As Integer = Win32.ScrollWin dowEx(Handle, 0, 10, rtin, rt,
IntPtr.Zero, rtout, 0)

To this:
Dim rr As Integer = Win32.ScrollWin dowEx(Handle, 0, 10, rectangle.empty ,
rectangle.empty , IntPtr.Zero, rectangle.empty , 0)

the whole screen scrolls as it should do, which kinda says the parameters
are wrong.

Can anyone help?

Scott