nanogui: Length of Window extra bytes.
Subject:
Re: Length of Window extra bytes.
From:
Chris Johns ####@####.####
Date:
17 Jan 2000 23:20:26 -0000
Message-Id: <3883A14A.61320928@acm.org>
Greg Haerr wrote:
>
> : I suspect I cannot use the extra bytes for storing the object pointer as
> : a SendMessage occurs and the object pointer is not loaded into the
> : window structure when this occurs.
> :
> : I added the "LPVOID lpParam" to the `struct hwnd' and set it. I also
> : added a macro to access it.
> :
>
> No, the extra bytes are just bytes adjacent to the struct hwnd. You don't
> want to add another element to struct hwnd, or every window takes
> up extra space. The proper way is to fill out the cbWndExtra field
> with as follows:
>
> wc.cbWndExtra = sizeof(LPVOID);
>
> before calling RegisterClass(). Then, in the window procedure
> for that class, under WM_CREATE:
>
> SetWindowLong(hwnd, 0, your_lpvoid);
>
> You can then always access this value with:
>
> pvoid = (LPVOID)GetWindowLong(hwnd, 0);
>
> As I check the source, you'll need to write SetWindowLong
> yourself, use microwin/src/mwin/winuser.c's SetWindowWord
> as a base, and return a *(LONG *) rather than *(WORD *)...
>
Oh. I assumed that the `lpParam' was just not implemented and was to be
implemented. What is the purpose of the `lpParam' parameter when
creating a window ?
I cannot use the WM_CREATE message as I do not yet know the relationship
between the C++ object and hwnd when my WndProc function is called
(assuming synchronous message sends).
I have a single `WndProc' function for all windows created using a
window class created with the WindowClass class (blah, too many
classes). In my common WndProc function I need to obtain the object
pointer so I can call a virtual method `HandleMessage'. This is my per
window object WndProc function.
I see in the demo code the `HMENU' window create parameter is really an
`id' and it is used to handle different windows from within a common
WndProc function. I would use `id' how-ever is only an `int' and I
cannot assume the size of int is large enough for a pointer.
--
Chris Johns, ####@####.####
