Set frame rate

Hello

I need in my app to set how many frames per sec. are drawn...

I use the GetTickCount() function but there appears a problem that the CPU is allways on 100% of usage...

I suppose maybe usage of else function or some other way how to detect the time flow...


Thx very much for support

If you use an endless loop, yes, you will use up 100% CPU. You need to Sleep.

Code:

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// Let's set it to update 50 frames/sec.
DWORD dwTickRate = 1000 / 50;
DWORD dwTick1 = 0; //GetTickCount();
DWORD dwSleepNeeded = dwTickRate;
for (int i = 0; i < 50; i++)
{
        Sleep(dwSleepNeeded); // Sleep for the amount of time necessary before next drawing
        dwTick1 = GetTickCount(); // Take a snapshot of current time
        // Call rendering
        dwSleepNeeded = dwTickRate - (GetTickCount() - dwTick1); // Calculate how much time we need to sleep
}

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Something like this should do the job.

Do you want to clamp the framerate or do you only want to display it??? If you want to clamp it you are wasting tons of cycles.

To Elysia:
Looks pretty interresting thank you very much

To Bubba:
In one case I only need the framerate for a sort of program and in second case I need it for stopwatch time

Remember, the code doesn't take into account that Sleeping for 50 ms doesn't necessarily sleep for 50 ms (it can sleep more), so it's not 100% exact. That may require additional complexity, but it gives you the idea how to do work 50 times per second with little overhead.

Quote:

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Originally Posted by Elysia

Remember, the code doesn't take into account that Sleeping for 50 ms doesn't necessarily sleep for 50 ms (it can sleep more), so it's not 100% exact. That may require additional complexity, but it gives you the idea how to do work 50 times per second with little overhead.

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Ok thx again

Remember that Sleep() will stop the app/thread doing anything else.

Quote:

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Originally Posted by Gordon

To Elysia:
In one case I only need the framerate for a sort of program and in second case I need it for stopwatch time

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For the stop watch have you looked at WM_TIMER msgs?

Can create a timer which will send you a msg every time period (50ms in this case). Is not that accurate (never better than 10ms). Timer msgs are very low priority in the OS msg queue and can be 'ignored' like paint msgs.

SetTimer()
KillTimer()

Quote:

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Originally Posted by novacain

Remember that Sleep() will stop the app/thread doing anything else.



For the stop watch have you looked at WM_TIMER msgs?

Can create a timer which will send you a msg every time period (50ms in this case). Is not that accurate (never better than 10ms). Timer msgs are very low priority in the OS msg queue and can be 'ignored' like paint msgs.

SetTimer()
KillTimer()

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I just tried the WM_TIMER but there is too many of laggs and it absolutely does not flow steadily... For stopwatch this is not appropriate for the second thing I am creating it is just OK... Thx for advise

Here's an interesting link on timer functions.

Code:

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        // Let's set it to update 50 frames/sec.
        const DWORD dwTimeFrame = 1000; // The time frame we're targeting (in ms)
        const DWORD dwFramesPerTimeFrame = 50; // Number of times per time frame cycle to do rendering
        const DWORD dwTickRate = dwTimeFrame / dwFramesPerTimeFrame; // Calculate amount of time to sleep each time
        INT32 nSleepNeeded; // Stores the amount of time we need to sleep
        DWORD dwTimeElapsed; // Time elapsed since beginning of time frame
        DWORD dwNextSleepBoundary; // The next "target" time to sleep until.
        DWORD dwTick; // Used to hold a snapshot of timeGetTime so we can calculate elapsed time
        DWORD Count = 1; // Simple counter just for cosmetics - just to print something
        DWORD dwTick2 = timeGetTime(); // Snapshot of the beginning of the code sample

        for(;;)
        {
                // Initialize variables
                nSleepNeeded = 0;
                dwTimeElapsed = 0;
                dwNextSleepBoundary = dwTickRate; // Set the next sleep boundary to the next tick.
                dwTick = timeGetTime(); // Get a snapshot of the current time
                while (dwNextSleepBoundary <= dwTimeFrame)
                {
                        // Call rendering here
                        dwTimeElapsed = timeGetTime() - dwTick; // Calculate elapsed time
                        nSleepNeeded = dwNextSleepBoundary - dwTimeElapsed; // Calculate amount of time we need to sleep (at least)
                        if (nSleepNeeded > 0) // Safesty check; we don't want to do Sleep(0) or sleep a negative value since Sleep takes a DWORD
                                Sleep(nSleepNeeded); // Sleep for the amount of time necessary before next drawing
                        dwNextSleepBoundary += dwTickRate; // Increase sleep "boundary" to next time frame tick
                        cout << Count++ << endl; // Print counter
                }
                DWORD dwTick3 = timeGetTime() - dwTick2; // Calculate amount of time the entire loop took
                cout << "Took " << dwTick3 << " ms!\n"; // Print out the time it took
                __asm int 3; // Do a debug break
        }

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Here's an updated code if you want it! It's more exact!
On my machine, it printed 1-50 and then "Took 1000 ms!".
Cool, huh? ;)

Cool... Now it works even better than I expected it would...

Thanks everyone especially "Elysia"