Using Delta for a stopwatch, delta too fast than real time seconds

Question

I search for methods to create a stopwatch on libgdx and came across with this:

public void trigger(float delta){

    playTime += delta;
    playTimeRounded = ((double)Math.round(playTime * 100) / 100);
    Gdx.app.log("deltaTime", delta + "");
}

But its not accurate and its much faster. How can i create an accurate stopwatch?

Answer 1

When you accumulate deltas you are also accumulating rounding errors.

Instead, record the system time the game started and compare it to the system time now.

Do not use time-of-day as this can get adjusted by internet-based time-of-day clock synchronization and other things.

Different OSes have different names for those clocks.

On windows you can use GetTickCount64 for this ( http://msdn.microsoft.com/en-us/library/windows/desktop/ms724411%28v=vs.85%29.aspx )

On linux you can use clock_gettime with CLOCK_MONOTIONIC (http://man7.org/linux/man-pages/man3/clock_gettime.3.html )

On OSX you can use clock_get_system_microtime ( https://developer.apple.com/library/mac/documentation/Darwin/Conceptual/KernelProgramming/services/services.html )

For Java use System.nanoTime()

Answer 2

Maybe your delta parameter has a wrong value when called. I prefer to use Gdx.graphics.getDeltaTime() instead.

float playTime = 0;
float playTimeRounded;

void AnyUpdateMethod()
{
    playTime += Gdx.graphics.getDeltaTime();
    playTimeRounded = Math.round(playTime * 100) / 100.0f;
    Gdx.app.log("playTimeRounded", playTimeRounded + "");
}

Answer 3

The deltaTime is the amount of time which passes between drawing two consecutive frames. It is used for updating things on your screen that change in time, for example when moving your objects around, you would want to apply the deltaTime to the object's speed, in order to have a consistent movement across devices. When calculating playtime though, you should only use the system time, increase it, decrease it normally, without applying any delta to it. You would have to store your playTime value as a long, since you are going to add to it the value of TimeUtils.millis(). Just forget about the deltaTime in this case.