Handling time¶
Time in pySFML¶
Unlike many other libraries where time is an int number of milliseconds, or a
float number of seconds, pySFML doesn’t impose any specific unit or type for
time values. Instead it leaves this choice to the user through a flexible
Time
. All pySFML classes and functions that manipulate time values
use this class.
Time
wraps a relative time value (in other words, a time span). It is
not a date-time class which would represent the current
year/month/day/hour/minute/second, 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 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 Time
:
t1 = sf.microseconds(10000)
t2 = sf.milliseconds(10)
t3 = sf.seconds(0.01)
Note that these three times are all equal.
Similarly, a Time
can be converted back to either seconds,
milliseconds or microseconds:
time = ...
usec = time.microseconds # long
msec = time.milliseconds # int
sec = time.seconds # float
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.
t1 = ... t2 = t1 * 2 t3 = t1 + t2 t4 = -t3
b1 = t1 == t2 b2 = t3 > t4
Measuring time¶
Now that we’ve seen how to manipulate time values with pySFML, let’s see how to do something that almost every program needs: measuring the time elapsed.
pySFML has a very simple class for measuring time: Clock
. It only has
two members: elapsed_time
, to retrieve the time elapsed since the
clock started, and restart()
, to restart the clock.
clock = sf.Clock() # starts the clock
# ...
elapsed1 = clock.elapsed_time
print(elapsed1.seconds)
clock.restart()
# ...
elapsed2 = clock.elapsed_time
print(elapsed2.seconds)
Note that restart also returns the elapsed time, so that you can avoid the
slight gap that would exist if you had to call elapsed_time
explicitly before restart.
Here is an example that uses the time elapsed at each iteration of the game
loop to update the game logic:
clock = sf.Clock()
while window.is_open:
elapsed = clock.restart()
update_game(elapsed)
#...