Handling Time

Time in DSFML

Just like the SFML implementation of time, DSFML doesn't impose a specific unit or type for time values. Instead it leaves this choice to the user through a flexible struct: Time. All DSFML classes and functions that manipulate time values use this class.

Time represents a time period (in other words, the time that elapses between two events). It is not a date-time class which would represent the current year/month/day/hour/minute/second as a timestamp, it's just a value that represents a certain amount of time, and how to interpret it depends on the context where it is used.

Converting time

A sf::Time value can be constructed from different source units: seconds, milliseconds and microseconds. A Time struct can also be constructed from the standard library `Duration` structure. There is are (non-member) functions to turn each of them into a Time:

auto t1 = microseconds(10000);
auto t2 = milliseconds(10);
auto t3 = seconds(0.01f);
auto t4 = duration(dur!"msecs"(10))

Note that these three times are all equal.

Similarly, a Time can be converted back to either seconds, milliseconds, microseconds or a Duration:

Time time = ...;

long         usec = time.asMicroseconds();
int          msec = time.asMilliseconds();
float        sec  = time.asSeconds();
Duration duration = time.asDuration();

Playing with time values

Time is just an amount of time, so it supports arithmetic operations such as addition, subtraction, comparison, etc. Times can also be negative.

Time t1 = ...;
auto t2 = t1 * 2;
auto t3 = t1 + t2;
auto t4 = -t3;

bool b1 = (t1 == t2);
bool b2 = (t3 > t4);

Measuring time

Now that we've seen how to manipulate time values with SFML, let's see how to do something that almost every program needs: measuring the time elapsed.

SFML has a very simple class for measuring time: Clock. It only has two functions: getElapsedTime, to retrieve the time elapsed since the clock started, and restart, to restart the clock.

auto clock = new Clock(); // starts the clock
...
Time elapsed1 = clock.getElapsedTime();
writeln(elapsed1.asSeconds());
clock.restart();
...
Time elapsed2 = clock.getElapsedTime();
writeln(elapsed2.asSeconds());

Note that restart also returns the elapsed time, so that you can avoid the slight gap that would exist if you had to call getElapsedTime explicitly before restart.

Here is an example that uses the time elapsed at each iteration of the game loop to update the game logic:

auto clock = new Clock();
while (window.isOpen())
{
    Time elapsed = clock.restart();
    updateGame(elapsed);
    ...
}