XProfan

Struct WNDCLASSEX = cbSize&,style&,lpfnWndProc&,cbClsExtra&,cbWndExtra&,hInstance&,hIcon&,hCursor&,hbrBackground&,\
lpszMenuName&,lpszClassName&,hIconSm&

proc Wndproc

    parameters wnd&,msg&,wp&,lp&
    return External("USER32","DefWindowProcA",wnd&,msg&,wp&,lp&)

endproc

cls
declare triangle#,trname$ : Dim triangle#,WNDCLASSEX : trname$ = "MyClass"

With Triangle#

    .cbSize& = SizeOf(triangle#)
    .style& = 3'CS_HREDRAW |CS_VREDRAW
    .lpfnWndProc& = ProcAddr(Wndproc,4)
    .cbClsExtra& = 0
    .cbWndExtra& = 0
    .hInstance& = %hInstance
    .hIcon& = External("USER32","LoadIconA",0,$7F00)'IDI_APPLICATION
    .hCursor& = External("USER32","LoadCursorA",0,$7F00)'IDC_CURSOR
    .hbrBackground& = 1'COLOR_BACKGROUND
    .lpszMenuName& = 0
    .lpszClassName& = Addr(trname$)
    .hIconSm& = .hIcon&

EndWith

var atom& = External("USER32","RegisterClassExA",triangle#)
print WinError$(%WinError)
Dispose triangle#

whilenot IsKey(27)

    waitinput

wend

atom& = External("USER32","UnregisterClassA",trname$,%hInstance)
print WinError$(%WinError)
waitinput
end