iczelion tut25[3]

  invoke dispatchmessage, addr msg
 .endw
 mov     eax,msg.wparam
 ret
winmain endp

wndproc proc hwnd:hwnd, umsg:uint, wparam:wparam, lparam:lparam
   local ps:paintstruct
   local hdc:hdc
   local hmemdc:hdc
   local rect:rect
   .if umsg==wm_create
      invoke loadbitmap,hinstance,idb_main
      mov hbitmap,eax
   .elseif umsg==wm_paint
      invoke beginpaint,hwnd,addr ps
      mov    hdc,eax
      invoke createcompatibledc,hdc
      mov    hmemdc,eax
      invoke selectobject,hmemdc,hbitmap
      invoke getclientrect,hwnd,addr rect
      invoke bitblt,hdc,0,0,rect.right,rect.bottom,hmemdc,0,0,srccopy
      invoke deletedc,hmemdc
      invoke endpaint,hwnd,addr ps
 .elseif umsg==wm_destroy
  invoke deleteobject,hbitmap
  invoke postquitmessage,null
 .else
  invoke defwindowproc,hwnd,umsg,wparam,lparam
  ret
 .endif
 xor eax,eax
 ret
wndproc endp
end start

;---------------------------------------------------------------------
;                            the resource script
;---------------------------------------------------------------------
#define idb_main 1
idb_main bitmap "tweety78.bmp"

analysis:

#define idb_main 1
idb_main bitmap "tweety78.bmp"

   .if umsg==wm_create
      invoke loadbitmap,hinstance,idb_main
      mov hbitmap,eax

in response to wm_create, we call loadbitmap to load the bitmap from the resource, passing the bitmap's resource identifier as the second parameter to the api. we get the handle to the bitmap when the function returns.
now that the bitmap is loaded, we can paint it in the client area of our main window.

   .elseif umsg==wm_paint
      invoke beginpaint,hwnd,addr ps
      mov    hdc,eax
      invoke createcompatibledc,hdc
      mov    hmemdc,eax
      invoke selectobject,hmemdc,hbitmap
      invoke getclientrect,hwnd,addr rect
      invoke bitblt,hdc,0,0,rect.right,rect.bottom,hmemdc,0,0,srccopy
      invoke deletedc,hmemdc
      invoke endpaint,hwnd,addr ps

we choose to paint the bitmap in response to wm_paint message. we first call beginpaint to obtain the handle to the device context. then we create a compatible memory dc with createcompatibledc. next select the bitmap into the memory dc with selectobject. determine the dimension of the client area with getclientrect. now we can display the bitmap in the client area by calling bitblt which copies the bitmap from the memory dc to the real dc. when the painting is done, we have no further need for the memory dc so we delete it with deletedc. end painting session with endpaint.

 .elseif umsg==wm_destroy
  invoke deleteobject,hbitmap