=====Changing the MDI background colour=====

// by Richard Russell, March 2007//\\ \\  If your program uses a **Multiple Document Interface**, by means of the [[http://www.bbcbasic.co.uk/bbcwin/manual/bbcwing.html#mdilib|MDILIB library]], the background of the **MDI client** area is filled with the **COLOR_APPWORKSPACE** system colour, which by default is a mid-grey. Although you can change this colour in Windows Control Panel that will affect all applications, which you probably don't want to do.\\ \\  It is possible to change the **MDI client** background colour just for your program by //subclassing// its window procedure. To do that you can use the following procedure:

<code bb4w>
        DEF PROCsubclassmdiclient
        LOCAL E%, M%, O%, P%
        DIM P% 99
        SYS "GetWindowLong", @hmdi%, -4 TO O%
        [OPT 2
        .E% ; WM_ERASEBKGND
        push [^MDIBkgdCol%]
        call "CreateSolidBrush"
        mov edx,[esp+12] ; hDC = wParam
        sub esp,16 ; Room for RECT
        mov ecx,esp
        push eax ; for DeleteObject
        push eax ; for FillRect
        push ecx ; for FillRect
        push edx ; for FillRect
        push ecx ; for GetClientRect
        push @hmdi%
        call "GetClientRect"
        call "FillRect"
        call "DeleteObject"
        add esp,16
        mov eax,1
        ret 16
        .M% cmp dword [esp+8],20 : jz E% : jmp O%
        ]
        SYS "SetWindowLong", @hmdi%, -4, M%
        ENDPROC
</code>

You should call this procedure immediately after initialising the Multiple Document Interface, as follows:

<code bb4w>
        PROC_initmdi(hWindowMenu%)
        MDIBkgdCol% = &800000
        PROCsubclassmdiclient
</code>

The MDI background colour will be set to whatever RGB value you load into **MDIBkgdCol%**, which in the above example is a dark blue.\\ \\  If you want to change the **MDI client** colour whilst your program is running, you will need to use code similar to the following to force the background to be refreshed:

<code bb4w>
        MDIBkgdCol% = &008000
        SYS "InvalidateRect", @hmdi%, 0, 1
</code>