Another drawback is that you cannot initialize local
variables automatically because they're just stack memory allocated dynamically
on function start. You have to manually assign them with desired values after
LOCAL directives.
mov wc.cbSize,SIZEOF WNDCLASSEX
mov wc.style, CS_HREDRAW or CS_VREDRAW
mov wc.lpfnWndProc, OFFSET WndProc
mov wc.cbClsExtra,NULL
mov wc.cbWndExtra,NULL
push hInstance
pop wc.hInstance
mov wc.hbrBackground,COLOR_WINDOW+1
mov wc.lpszMenuName,NULL
mov wc.lpszClassName,OFFSET ClassName
invoke LoadIcon,NULL,IDI_APPLICATION
mov wc.hIcon,eax
mov wc.hIconSm,0
invoke LoadCursor,NULL,IDC_ARROW
mov wc.hCursor,eax
invoke RegisterClassEx, addr wc
; register our window class
The inimidating lines above are really simple in concept. It just takes several
lines of instruction to accomplish. The concept behind all these lines is
window class. A window class is nothing more than a blueprint or specification
of a window. It defines several important characteristics of a window such as
its icon, its cursor, the function responsible for it, its color etc. You
create a window from a window class. This is some sort of object oriented
concept. If you want to create more than one window with the same character-
istics, it stands to reason to store all these characteristics in only one
place and refer to them when needed. This scheme will save lots of memory by
avoiding duplication of information.
Remember, Windows is designed in the past when memory chips are prohibitive and
most computers have 1 MB of memory. Windows must be very efficient in using the
scarce memory resource. The point is: if you define your own window, you must
fill the desired characteristics of your window in a WNDCLASS or WNDCLASSEX
structure and call RegisterClass or RegisterClassEx before you're able to
create your window. You only have to register the window class once for each
window type you want to create a window from.
Windows have several predefined Window classes, such as button and edit box.
For these windows (or controls), you don't have to register a window class,
just call CreateWindowEx with the predefined class name.
The single most important member in the WNDCLASSEX is lpfnWndProc. lpfn stands
for long pointer to function. Under Win32, there's no "near" or "far" pointer,
just pointer because of the new FLAT memory model. But this is again a lefover
from the day of Win16. Each window class must be associated with a function
called window procedure. The window procedure is responsible for message
handling of all windows created from the associated window class.
Windows will send messages to the window procedure to notify it of important
events concerning the windows it 's responsible for,such as user keyboard or
mouse input. It's up to the window procedure to respond intelligently to each
window message it receives. You will spend most of your time writing event
handlers in window procedure.
I'll describe each member of WNDCLASSEX below:
typedef struct tagWNDCLASSEX {
UINT cbSize;
UINT style;
WNDPROC lpfnWndProc;
int cbClsExtra;
int cbWndExtra;
HINSTANCE hInstance;
HICON hIcon;
HCURSOR hCursor;
HBRUSH hbrBackground;
LPCSTR lpszMenuName;
LPCSTR lpszClassName;
HICON hIconSm;
} WNDCLASSEX;
cbSize: The size of WNDCLASSEX structure in bytes. We can use SIZEOF operator
to get the value.
style: The style of windows created from this class. You can combine several
styles together using "or" operator.
lpfnWndProc: The address of the window procedure responsible for windows
created from this class.
cbClsExtra: Specifies the number of extra bytes to allocate following the
window-classstructure. The operating system initializes the bytes to zero.
cbWndExtra: Specifies the number of extra bytes to allocate following the window
instance. The operating system initializes the bytes to zero. If an application
uses the WNDCLASS structure to register a dialog box created by using the CLASS
directive in the resource file, it must set this member to DLGWINDOWEXTRA.
hInstance: Instance handle of the module.
hIcon: Handle to the icon. Get it from LoadIcon call.
hCursor: Handle to the cursor. Get it from LoadCursor call.
hbrBackground: Background color of windows created from the class.
lpszMenuName: Default menu handle for windows created from the class.
lpszClassName: The name of this window class.
hIconSm: Handle to a small icon that is associated with the window class. If
this member is NULL, the system searches the icon resource specified by the
hIcon member for an icon of the appropriate size to use as the small icon.
invoke CreateWindowEx, NULL,\
ADDR ClassName,\
ADDR AppName,\
WS_OVERLAPPEDWINDOW,\
CW_USEDEFAULT,\
CW_USEDEFAULT,\
CW_USEDEFAULT,\
CW_USEDEFAULT,\
NULL,\
NULL,\
hInst,\
NULL
After registering the window class, we can call CreateWindowEx to create our
window based on the submitted window class. Notice that there're 12 parameters
to this function. C function prototype of CreateWindowEx is below:
HWND
WINAPI
CreateWindowExA(
DWORD dwExStyle,
LPCSTR lpClassName,
LPCSTR lpWindowName,
DWORD dwStyle,
int X,
int Y,
int nWidth,
int nHeight,
HWND hWndParent ,
HMENU hMenu,
HINSTANCE hInstance,
LPVOID lpParam);
Let's see detailed description of each parameter:
dwExStyle: Extra window styles. This is the new parameter that is added to the
old CreateWindow. You can put new window styles for Windows 95 & NT here. You
can specify your ordinary window style in dwStyle but if you want some special
styles such as topmost window, you must specify them here. You can use NULL if
you don't want extra window styles.
lpClassName: (Required). Address of the ASCIIZ string containing the name of
window class you want to use as template for this window. The Class can be your
own registered class or predefined window class. As stated above, every window
you created must be based on a window class.
lpWindowName: Address of the ASCIIZ string containing the name of the window.
It'll be shown on the title bar of the window. If this parameter is NULL, the
title bar of the window will be blank.
dwStyle: Styles of the window. You can specify the appearance of the window
here. Passing NULL is ok but the window will have no system menu box, no
minimize-maximize buttons, and no close-window button. The window would not be
of much use at all. You will need to press Alt+F4 to close it. The most common
window style is WS_OVERLAPPEDWINDOW. A window style is only a bit flag. Thus
you can combine several window styles by "or" operator to achieve the desired