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Handling time
Time in SFML
Unlike many other libraries where time is a uint32 number of milliseconds, or a float number of seconds, SFML doesn't impose any specific unit or
type for time values. Instead it leaves this choice to the user through a flexible class: sf::Time
. All SFML classes and functions
that manipulate time values use this class.
sf::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. There is a (non-member)
function to turn each of them into a sf::Time
:
sf::Time t1 = sf::microseconds(10000);
sf::Time t2 = sf::milliseconds(10);
sf::Time t3 = sf::seconds(0.01f);
Note that these three times are all equal.
Similarly, a sf::Time
can be converted back to either seconds, milliseconds or microseconds:
sf::Time time = ...;
sf::Int64 usec = time.asMicroseconds();
sf::Int32 msec = time.asMilliseconds();
float sec = time.asSeconds();
Playing with time values
sf::Time
is just an amount of time, so it supports arithmetic operations such as addition, subtraction, comparison, etc.
Times can also be negative.
sf::Time t1 = ...;
sf::Time t2 = t1 * 2;
sf::Time t3 = t1 + t2;
sf::Time 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: sf::Clock
. It only has two functions: getElapsedTime
, to retrieve
the time elapsed since the clock started, and restart
, to restart the clock.
sf::Clock clock; // starts the clock
...
sf::Time elapsed1 = clock.getElapsedTime();
std::cout << elapsed1.asSeconds() << std::endl;
clock.restart();
...
sf::Time elapsed2 = clock.getElapsedTime();
std::cout << elapsed2.asSeconds() << std::endl;
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:
sf::Clock clock;
while (window.isOpen())
{
sf::Time elapsed = clock.restart();
updateGame(elapsed);
...
}