MS Windows Subclassing

[geezer9]

Dear oldwinapi experts:

I am trying to subclass the standard MS Windows "BUTTON" class, but wierd stuff 
keeps happening. The code shown below compiles and runs. The top button works, 
but the button below does not change state. WORSE, once it is exercised, 
whatever was done wrong now stops the top button from working.

There must be something about using a LONG_PTR variable as a WNDPROC in 
CallWindowProc that I am doing wrong.

BTW I am developing on Linux using Wine, the compilation command is:
    
    
    nim --cpu:i386 --os:windows -o:msnb2forum.exe -r c msnb2forum.nim
    

and the nim.cfg file in the source folder is:
    
    
    i386.windows.gcc.path = "/usr/bin"
    i386.windows.gcc.exe = "i686-w64-mingw32-gcc"
    i386.windows.gcc.linkerexe = "i686-w64-mingw32-gcc"
    

H E L P !
    
    
    import strutils
    import windows
    var appInstance*:HINST = 0
    
    proc makeWinClass(name:string,wndProc:WNDPROC,backgnd:HANDLE) =
        if appInstance==0:
            appInstance = GetModuleHandle(nil)
        var wndclass:WNDCLASS
        wndclass.style         = CS_HREDRAW or CS_VREDRAW
        wndclass.lpfnWndProc   = wndProc
        wndclass.cbClsExtra    = 0
        wndclass.cbWndExtra    = 0
        wndclass.hInstance     = appInstance
        wndclass.hIcon         = LoadIcon(0, IDI_APPLICATION)
        wndclass.hCursor       = LoadCursor(0, IDC_CROSS)
        wndclass.hbrBackground = backgnd        # GetStockObject(WHITE_BRUSH)
        wndclass.lpszMenuName  = nil
        wndclass.lpszClassName = name
        if RegisterClass(addr wndclass) == 0:
            raise newException(Exception,"makeWinClass FAILS")
    
    proc bareWndProc(hWnd:HWND,message:WINUINT,wParam:WPARAM,lParam:LPARAM): 
LRESULT{.stdcall.} =
        return DefWindowProc(hWnd, message, wParam, lParam)
    
    var btnwndpr:LONG_PTR
    
    proc bscWndProc(hWnd:HWND,message:WINUINT,wParam:WPARAM,lParam:LPARAM): 
LRESULT{.stdcall.} =
        echo("in bscWndProc hWnd=",hWnd.toHex(8)," message=",message.toHex(4))
        var cwpRes = 
CallWindowProc(cast[WNDPROC](btnwndpr),hWnd,message,wParam,lParam)
        echo("cwpRes=",cwpRes.toHex(8))
        return cwpRes
    
    makeWinClass("BARE",bareWndProc,GetStockObject(WHITE_BRUSH))
    
    proc mainLoop*() =
        var msg:MSG
        while GetMessage(addr msg, 0, 0, 0) != 0:
            discard TranslateMessage(addr msg)
            discard DispatchMessage(addr msg)
    
    var hmain:HWND = CreateWindowEx(
        0.DWORD,    # extended window style
        "BARE","Bare Bones",WS_THICKFRAME or WS_MAXIMIZEBOX or WS_MINIMIZEBOX 
or WS_SYSMENU,
        20.DWORD,30.DWORD,300.DWORD,200.DWORD,
        0.HWND,0.HMENU,appInstance,cast[LPVOID](0))
    
    var btn1:HWND = CreateWindowEx(
        0.DWORD,    # extended window style
        "BUTTON","quit app",WS_CHILD or WS_VISIBLE,
        10.DWORD,10.DWORD,80.DWORD,24.DWORD,
        hmain,0.HMENU,appInstance,cast[LPVOID](0))
    
    btnwndpr = GetWindowLongPtr(btn1,GWL_WNDPROC)
    makeWinClass("BTNSC",bscWndProc,GetStockObject(GRAY_BRUSH))
    
    var btn2:HWND = CreateWindowEx(
        0.DWORD,    # extended window style
        "BTNSC","sub btn",WS_CHILD or WS_VISIBLE,
        10.DWORD,40.DWORD,80.DWORD,24.DWORD,
        hmain,0.HMENU,appInstance,cast[LPVOID](0))
    
    discard ShowWindow(hmain, SW_SHOW)
    
    mainLoop()