PollEvent() in Win32 - windows

Question

I'm trying to mimic SFML's PollEvent(Event &event) function in Windows. It seems far more complicated that I imagined. Note that I already encapsulated the window procedure function in my class.
There could be many "window events" in my program - WindowMoved, WindowResized etc.
My first attempt was to have a private data member in the class, defined as WindowEvent *_lastWindowEvent. This variable will be set if PeekMessage() returns a non-zero value, just before DispatchMessage() is called. Then, winProc() will edit _lastWindowEvent, depending on the message it will receive.
The drawback here is that I noticed that winProc() may be called with a MSG parameter regardless of DispatchMessage(), like with the WM_SETCURSOR message.
Then I thought about having instead a std::queue<WindowEvent> in my class, when winProc() continuously pushes WindowEvents to it. The problem here is that sometimes the window procedure function keeps getting messages and won't return. This happens when I drag-move the window (then the WM_MOVING message is continuously called, along with other messages). The code after DispatchMessage() will not run until I release my mouse. This also happens when resizing the window.
Did I grasp anything wrong? How do you think such PollEvent function can be implemented?

Answer 1

Given that PollEvent is primarily for a game loop style design, you can probably poll for what you need while simultaneously servicing the Windows event loop:
class Window
{
HWND _hwnd; // Win32 handle to the window
RECT _lastWindowSize; // last known window size
POINT _lastMousePos; // last known mouse position on window
BYTE _lastKeyboardState[256]; // last known key state
std::list<Event> _events; // unprocessed events
public:
bool PollEvent(Event* pEvent);
};
bool Window::PollEvent(Event* pEvent)
{
// return any previously queued events
if (_events.size() > 0)
{
*pEvent = _events.pop_front();
return true;
}
// process 1 windows event message
if (PeekMessage(&msg, _hWnd, 0, 0, PM_REMOVE))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
if (msg.msg == WM_QUIT)
{
*pEvent = EXIT_EVENT; // special handling for WM_QUIT
return true;
}
}
// -----------------------------------------
// poll keyboard state
BYTE kbState[256];
GetKeyboardState(kbState);
bool isKeyboardEvent = false;
if (memcmp(_lastKeyboardState, kbState, 256) != 0)
{
// not shown
// compute diff of kbState and _lastKeyboardState
// generate a keyboard event and add to the queue
Event kbevt;
kbevt.type = KeyEvent;
kbevt.code = <computed code based on diff above>
_events.push_back(kbevt);
}
memcpy(_lastKeyboardState, kbState, 256);
// -----------------------------------------
// -----------------------------------------
// poll window size changes
RECT rectWindowSize;
int width, height, oldwidth, oldheight;
GetClientRect(&rectWindowSize);
width = rectWindowSize.right - rectWindowSize.left;
height = rectWindowSize.bottom - rectWindowSize.top;
oldwidth = _lastWindowSize.right - _lastWindowSize.left;
oldheight = _lastWindowSize.bottom - _lastWindowSize.top;
if ((width != oldwidth) || (height != oldheight))
{
Event sizeEvent;
sizeEvent.type = SizeEvent;
sizeEvent.width = width;
sizeEvent.height = height;
_events.push_back(kbevt);
}
_lastWindowSize = rectWindowSize;
// -----------------------------------------
// not shown - computing mouse position, joystick position, text stuff
// if at least one event was queued - return it now
if (_events.size() > 0)
{
*pEvent = _events.pop_front();
return true;
}
return false;
}