NCCALCSIZE TO MAKE A SPACE

WVR_ALIGNBOTTOM = 64

WVR_ALIGNLEFT = 32

WVR_ALIGNRIGHT = 128

WVR_ALIGNTOP = 16

WVR_HREDRAW = 256

WVR_REDRAW = WVR_HREDRAW + WVR_VREDRAW

WVR_VALIDRECTS = 1024

WVR_VREDRAW = 512

Type RECT

left As Long

right As Long

top As Long

bottom As Long

End Typd

Type NCCALCSIZE_PARAMS

rgrc(3) As RECT

lppos As WINDOWPOS

End Type 

Type WINDOWPOS

x As Long

y As Long

cx As Long    ' width

cy As Long    ' heigth

End Type

Dim tNCR As NCCALCSIZE_PARAMS 

Dim tWP As WINDOWPOS

If wParam <> 0 Then

 lParam containts a pointer to the'

 NCCALCSIZE_PARAMS structure: 

(CopyMemory tNCR,ByVal lParam, Len(tNCR

 the NCCALCSIZE_PARAMS structure contains'

 a pointer to the WINDOWPOS structure: 

(CopyMemory tWP,ByVal tNCR.lppos, Len(tWP

 Set the first rectangle to the WINDOWPOS ' size'

(With tNCR.rgrc(0

Left=tWP.x.

Top=tWP.y.

Right=tWP.x+tWP.cx.

Bottom = tWP.y + tWP.cy.

End With

Now modify the rectangle if we're showing tabs'

 to allow space for the tab strip itself'

If (m_bShowTabs) Then 

tNCR.rgrc(0).Left=tNCR.rgrc(0).Left+2

tNCR.rgrc(0).Right=tNCR.rgrc(0).Right-2

If (m_eTabAlign=TabAlignBottom) Then

tNCR.rgrc(0).Top=tNCR.rgrc(0).Top+2

tNCR.rgrc(0).Bottom=tNCR.rgrc(0).Bottom-m_lTabHeight

Else

tNCR.rgrc(0).Top=tNCR.rgrc(0).Top+m_lTabHeight

tNCR.rgrc(0).Bottom=tNCR.rgrc(0).Bottom-2 

End If 

End If

 Set the second rectangle to equal the first'

(tNCR.rgrc(1)=tNCR.rgrc(0

CopyMemory ByVal lParam,tNCR, Len(tNCR) ' Tell 

 :Windows we've modified the size'

ISubclass_WindowProc=WVR_VALIDRECTS

Once this is done, there will be a space for the tabs

Case WM_NCPAINT 

 Ensure the standard mon-client drawing is' 

:completed

(ISubclass_WindowProc=CallOldWindowProc(hWnd,iMsg,wParam,lParam

 Do custom drawing: first get a DC to the non-client' 

:area

Dim lhDC As Long 

(lhDC=GetWindowDC(hWnd

'.... Now can draw in the area we've cleared'

  Clear up DC '

ReleaseDC lHDC, hWnd

Check the actual source code for the details of drawing the tabs. The code uses an EnumWindowsProc callback function to determine all of the windows within the MDIClient area, and the WM_MDIGETACTIVEmessage to determine which 

.(window is the currently selected MDI child (if any

Finally, we need to intercept the user clicking on a tab or button within the tab control. There are two messages Windows sends to the non-client area to allow you to 

:check for mouse events

WM_NCHITTEST

This message allows you to tell Windows that a non-client area should be treated in a particular way, such as title bar or size gripper.

WM_SETCURSOR

This message is used by Windows to determine which cursor to display, however, since it provides the type of mouse action being performed you can use it to determine mouse movement and button presses in the 

.area