Define a callback to process events.

In winMain set winClass.lpfnWndProc = <callback fn name>

Where:

LRESULT CALLBACK WinProc(HWND hWnd,

UINT msg,

WPARaM wParam,

LPARAM lParam);

where some common msg are:

Value	Meaning
WM_ACTIVATE	window activated/got focus
WM_CLOSE	window was closed
WM_CREATE	window just created
WM_DESTROY	window will be killed
WM_MOVE	window has been moved
WM_MOUSEMOVE	mouse has been moved
WM_KEYUP	key released
WM_KEYDOWN	key pressed
WM_TIMER	timer event occurred
WM_USER	user generated msg
WM_PAINT	window need repainting
WM_QUIT	application terminating
WM_SIZE	resize event

// bare bones event handler

LRESULT CALLBACK WindowProc(HWND hwnd, UINT msg, WPARAM wparam,
                                                                 LPARAM lparam)

{ // this function will handle msgs sent

HDC hdc; // device context for graphics

PAINTSTRUCT ps; // also for graphics

switch (msg) // process the message

{ case WM_CREATE:

{ // this msg sent on window creation

// do init stuff here

return(0);

} break;

case WM_PAINT:

{ // repaint the window

hdc = BeginPaint(hwnd.&ps); // get device context

// paint window here

EndPaint(hwnd, &ps); //tells Windows we repainted

return(0);

} break;

case WM_DESTROY

{ // clean up

PostQuitMessage(0);

// this will cause system to send WM_QUIT msg

return(0);

} break;

default: break;

}

// make Windows handle any msg you didn’t

return(DefWindowProc(hwnd, msg, wparam, lparam));

}

Messages - description

typedef struct tagMSG

{ HWND hwnd; // id msg sent to

UINT message; // msg id

WPARAM wParam; // more msg info

LPARAM lParam; // more msg info

DWORD time; // time of msg event

POINT pt; // mouse state of event

} MSG;

Need 3 functions to deal with msgs in the event loop.

1. To retrieve a message from the queue call:

BOOL GetMessage(LPMSG lpMsg, // ptr to message

HWND hWnd, // handle of window

UINT wMsgFilterMin; // 1^st msg

UINT wMsgFilterMax); // last msg

If the queue is empty the function waits for a msg.

2. Translate accelerator commands (^A) into basic events, by calling:

BOOL TranslateMessage( CONST MSG *lpMsg);

3. Send the msg address to event handler, with:

LONG DispatchMessage(CONST MSG *lpmsg);

Most windows programs then use these three functions to write an event loop like:

// even loop

while(GetMessage(&msg, NULL, 0, 0))

{ // translate the accelerator keys

TranslateMessage(&msg);

// send the msg to event handler

DispatchMessage(&msg);

}

The problem is that if there are no messages, it waits. This won’t work for a game because the display needs to be refreshed. We need to detect if a msg is available.

BOOL PeekMessage(&msg, NULL, 0, 0, PM_REMOVE);

this command examines the msg queue, removes it and returns true or returns false if no msg is available. You could also use PM_NOREMOVE to check w/o removing.

Now you can write a game event loop!

MSG msg; // holds msg

// game event loop

while(1)

{ // check for a message & process

if (PeekMessage(&msg, NULL,0, 0, PM_REMOVE)

{ // test for QUIT

if (msg.message == WM_QUIT)

break; // leave the loop

// translate

TranslateMessage(&msg);

// send to event handler – WinProc()

DispatchMessage(&msg);

}

// main game code goes here

}// end game loop