C / C++ / MFC

15-Jan-07 13:46

Would somebody be so kind as to show me exactly how to create a non-named event with an EVENT_MODIFY_STATE access rights. This is to be used with a multimedia timer but my events are never being triggered. All the examples I can find are for named events Sniff | :^)

Mark Salsbery15-Jan-07 14:13

15-Jan-07 14:13

I always just use CreateEvent().

hTimerEvent = ::CreateEvent(NULL, false, false, NULL);

and pass (LPTIMECALLBACK)hTimerEvent to ::timeSetEvent() with the TIME_CALLBACK_EVENT_SET timer
event type.

Mark

Waldermort15-Jan-07 15:33

15-Jan-07 15:33

Mark Salsbery wrote:
I always just use CreateEvent().

Strange, I can't get it to work for me. Here's the layout

I create the Event and the timer from my main thread, I launch a seperate thread which calls WaitForMultipleObjects(). I then call ResetEvent() and inform the main thread the evvent has occured. But! the event doesn't occur no matter what paramaters I call the various functions with.

Could this be some sort of thread related problem?

Mark Salsbery15-Jan-07 15:40

15-Jan-07 15:40

WalderMort wrote:
I then call ResetEvent()...

Reset? It's a manual reset event then?

WaitForMultipleObjects() never returns?

Waldermort15-Jan-07 16:04

15-Jan-07 16:04

I have tried both manual and auto resets, neither work. I have also tried named events, they don't work either. WaitForMultipleObjects() doesn't indicate that the event is set, but then it's on a 500ms timeout to prevent locking the handles.

Everything works perfectly if I use a callback function, but that's not what I want.

From MSDN:
"Any thread of the calling process can specify the event-object handle in a call to one of the wait functions.

So my code should be working.

Mark Salsbery15-Jan-07 14:34

15-Jan-07 14:34

Some sample code...

UINT wTimerRes = 0;
MMRESULT mmTimerId = 0;
HANDLE hTimerEvent = ::CreateEvent(NULL, false, false, NULL);
 
TIMECAPS tc;
if (::timeGetDevCaps(&tc, sizeof(TIMECAPS)) == TIMERR_NOERROR) 
{
   // Try for 1ms resolution - accept best
   wTimerRes = min(max(tc.wPeriodMin, 1), tc.wPeriodMax);
   ::timeBeginPeriod(wTimerRes); 
 
   // Set periodic 500ms timer
   mmTimerId = ::timeSetEvent(500, wTimerRes, (LPTIMECALLBACK)hTimerEvent, (DWORD_PTR)0, 
                           TIME_PERIODIC | TIME_CALLBACK_EVENT_SET);
}
 
 
// loop waiting on hTimerEvent (500ms x 10 = 5s)
int n = 0;
while (n < 10)
{
  ::WaitForSingleObject(hTimerEvent, INFINITE);
   n++;
}
 
 
if (mmTimerId)
{
   ::timeKillEvent(mmTimerId);
   mmTimerId = 0;
   ::timeEndPeriod(wTimerRes);
   wTimerRes = 0;
}
::CloseHandle(hTimerEvent);
hTimerEvent = NULL;

Waldermort16-Jan-07 1:33

16-Jan-07 1:33

Just an update. I never could get the multimedia timers to work with more than one event. I ended up changing the code slightly.

I now create an event for each timer just as before, but I create the timer using a callback function. Within this function I set the event ( which is what MMtimer is supposed to do! ). I then run a thread which waits on these events and does whatever the user intended.

Mark Salsbery16-Jan-07 6:58

16-Jan-07 6:58

hmmm beats me. I tested the code I posted before posting it.

Here's how I wait in many of my thread procs...maybe there's something that's different than
yours...

while (1)
{
   #define EVENT_TIMER      0
   #define EVENT_TERMINATE  1
 
   HANDLE Events[] =
   {
      hTimerEvent,
      hTerminateEvent
   };
 
   DWORD dwEventIndex = ::WaitForMultipleObjects(sizeof(Events) / sizeof(HANDLE),
                                    Events, FALSE, INFINITE);
 
   if (dwEventIndex == WAIT_FAILED)
   {
      break;
   }
 
   dwEventIndex -= WAIT_OBJECT_0;
 
   if (dwEventIndex == EVENT_TERMINATE)
   {
      break;
   }
 
... timer event occurred - do something
 
} //while (1)

Waldermort16-Jan-07 7:27

16-Jan-07 7:27

The only real difference is that I use dynamic arrays, but on watching through the debugger, the correct values are being passed in. Thinking that may be the problem, I instructed the thread to copy the handles to it's own 'stack based' array, the problem didn't go away.

I then thought that the events may be being set at exactly the same time ( Wait... returns only 1 index in such a case ) and tried a manual set and reset, no luck. Even with wait INFINITE for all objects.

I must try the same with other object like mutex's, it may be a bug within windows vista.

One question though, the docs say a timer is run in it's own thread. I set two timers and 1 worker thread. The 'task manager' states my exe has only 3 threads. So I'm guessing MMtimer creates a single thread to watch all timers, is this correct?

Mark Salsbery16-Jan-07 7:42

Question re Turret Rotation for video game

16-Jan-07 7:42

WalderMort wrote:
I then thought that the events may be being set at exactly the same time
( Wait... returns only 1 index in such a case )

That's definitely a possibility. If you need to differentiate between which timer event occurred
then you'd have to use separate events instead of sharing one event. I would think sharing
an event would kind of negate the need for the precision of a multimedia timer anyway.

WalderMort wrote:
I set two timers and 1 worker thread. The 'task manager' states my exe has only 3 threads.
So I'm guessing MMtimer creates a single thread to watch all timers, is this correct?

I know nothing about the internals of the multimedia timers, sorry Smile | :)

I would guess that none
of the timer threads are in your/our process though (kernel?), so maybe they don't show up...

From this article: Results from a Latency Study of Windows NT[^]
"Multimedia timers are implemented by spawning a high-priority thread that sets a kernel timer
and then blocks. Upon awakening the thread executes a callback routine provided by the user,
schedules its next wakeup, and then goes back to sleep."

It's interesting that it's not working as advertised for you. I've never had any probs with the
multimedia timers but I do hope my software runs on Vista Smile | :)

Does the first code sample I posted work for you? That code can be inserted anywhere - it
doesn't need a separate thread.

Mark

XKonSoftware15-Jan-07 12:37

XKonSoftware

15-Jan-07 12:37

I am currently working on a 2D shooter game, and I would like to be able to include enemy turrets that will be able to rotate towards the player to be able to fire at the player. The turrets have an angle variable, which stores which angle they are currently being rotated by (so which direction they're facing), and I want them to be able to track the player and determine which direction to turn to face the player the quickest. Let me attempt to explain this graphically
--------
Player
--------
--------
Turret -----> Current Firing Direction
--------
In this situation, assuming the player is 135 degrees from the turret, and the turret's rotation is 0, how can I make the turret understand that the best way to track the player is by rotating counterclockwise instead of clockwise? I have tried several methods, including attempts at using the dot products of the 2 vectors, etc. If anyone has any suggestions all help will be appreciated! Thanks!
-Steve

Re: Question re Turret Rotation for video game

Stephen Hewitt15-Jan-07 15:06

Stephen Hewitt

15-Jan-07 15:06

You could use the cross product[^]. To cut a long story short use this formula:

dir = x₁.y₂-x₂.y₁

Note that "." means multiply and only the sign of "dir" is of interest: +ve means anticlockwise and -ve clockwise, or the opposite if you're using a 4th quadrant coordinate system (which is probably the case here). (x₁, y₁) is the coordinates of the end of the turret on the firing ship, relative to the base of the turret. (x₂, y₂) is the point you're aiming for, relative to the base of the turret on the firing ship.

Steve

Re: Question re Turret Rotation for video game

Stephen Hewitt16-Jan-07 12:09

Stephen Hewitt

16-Jan-07 12:09

So, any luck?

Steve

Re-installed XP Pro.. No more GDI+

Dustin Henry15-Jan-07 12:33

Dustin Henry

15-Jan-07 12:33

I recently formatted and reinstalled XP Pro on one of my machines and now my application that uses GDI+ for font rendereing does not display the text. I have searched MSDN and found a GDI+ redistributable but it says it is only for 2000 and that you should use the system-supplied one for XP.

Any idea why this doesn't appear to have been installed with XP and where I can get the file?

Thanks,
Dustin

IOCP and ERROR_IO_PENDING

Polity4h15-Jan-07 11:15

Polity4h

15-Jan-07 11:15

Hi,

Im creating a server using UDP and IOCP.
I've red some articles about it and i understand the most of it ( the basic anyway. not saying im a IOCP master )
anyway, since i got a lot of ERROR_IO_PENDING returns when doing a WSASendTo or WSARecvFrom, i got myself wondering what hapends when i get this error. I know what it means but i dont quit seem to get or find any information about how to process it. What hapends when a send or recv function returns this and what is the best way of processing it?

Thanks already!

Re: IOCP and ERROR_IO_PENDING

Mark Salsbery15-Jan-07 11:55