ClockObject

class ClockObject

Bases: ReferenceCount

A ClockObject keeps track of elapsed real time and discrete time. In normal mode, get_frame_time() returns the time as of the last time tick() was called. This is the “discrete” time, and is usually used to get the time as of, for instance, the beginning of the current frame.

In other modes, as set by set_mode() or the clock-mode config variable, get_frame_time() may return other values to simulate different timing effects, for instance to perform non-real-time animation. See set_mode().

In all modes, get_real_time() always returns the elapsed real time in seconds since the ClockObject was constructed, or since it was last reset.

You can create your own ClockObject whenever you want to have your own local timer. There is also a default, global ClockObject intended to represent global time for the application; this is normally set up to tick every frame so that its get_frame_time() will return the time for the current frame.

Inheritance diagram

enum Mode

enumerator M_normal = 0

enumerator M_non_real_time = 1

enumerator M_forced = 2

enumerator M_degrade = 3

enumerator M_slave = 4

enumerator M_limited = 5

enumerator M_integer = 6

enumerator M_integer_limited = 7

ClockObject(ClockObject::Mode mode = M_normal)

ClockObject(ClockObject const &copy)

double calc_frame_rate_deviation(Thread *current_thread = Thread::get_current_thread()) const

Returns the standard deviation of the frame times of the frames rendered over the past get_average_frame_rate_interval() seconds. This number gives an estimate of the chugginess of the frame rate; if it is large, there is a large variation in the frame rate; if is small, all of the frames are consistent in length.

A large value might also represent just a recent change in frame rate, for instance, because the camera has just rotated from looking at a simple scene to looking at a more complex scene.

bool check_errors(Thread *current_thread)

Returns true if a clock error was detected since the last time check_errors() was called. A clock error means that something happened, an OS or BIOS bug, for instance, that makes the current value of the clock somewhat suspect, and an application may wish to resynchronize with any external clocks.

double get_average_frame_rate(Thread *current_thread = Thread::get_current_thread()) const

Returns the average frame rate in number of frames per second over the last get_average_frame_rate_interval() seconds. This measures the virtual frame rate if the clock is in M_non_real_time mode.

double get_average_frame_rate_interval(void) const

Returns the interval of time (in seconds) over which get_average_frame_rate() averages the number of frames per second to compute the frame rate.

static TypeHandle get_class_type(void)

double get_degrade_factor(void) const

In degrade mode, returns the ratio by which the performance is degraded. A value of 2.0 causes the clock to be slowed down by a factor of two (reducing performance to 1/2 what would be otherwise).

This has no effect if mode is not M_degrade.

double get_dt(Thread *current_thread = Thread::get_current_thread()) const

Returns the elapsed time for the previous frame: the number of seconds elapsed between the last two calls to tick().

int get_frame_count(Thread *current_thread = Thread::get_current_thread()) const

Returns the number of times tick() has been called since the ClockObject was created, or since it was last reset. This is generally the number of frames that have been rendered.

double get_frame_time(Thread *current_thread = Thread::get_current_thread()) const

Returns the time in seconds as of the last time tick() was called (typically, this will be as of the start of the current frame).

This is generally the kind of time you want to ask for in most rendering and animation contexts, since it’s important that all of the animation for a given frame remains in sync with each other.

ClockObject *get_global_clock(void)

Returns a pointer to the global ClockObject. This is the ClockObject that most code should use for handling scene graph rendering and animation.

double get_long_time(void) const

Returns the actual number of seconds elapsed since the ClockObject was created, or since it was last reset.

This is similar to get_real_time(), except that it uses the most accurate counter we have over a long period of time, and so it is less likely to drift. However, it may not be very precise for measuring short intervals. On Windows, for instace, this is only accurate to within about 55 milliseconds.

double get_max_dt(void) const

Returns the current maximum allowable time elapsed between any two frames. See set_max_dt().

double get_max_frame_duration(Thread *current_thread = Thread::get_current_thread()) const

Returns the maximum frame duration over the last get_average_frame_rate_interval() seconds.

Mode get_mode(void) const

Returns the current mode of the clock. See set_mode().

double get_net_frame_rate(Thread *current_thread = Thread::get_current_thread()) const

Returns the average frame rate since the last reset. This is simply the total number of frames divided by the total elapsed time. This reports the virtual frame rate if the clock is in (or has been in) M_non_real_time mode.

double get_real_time(void) const

Returns the actual number of seconds elapsed since the ClockObject was created, or since it was last reset. This is useful for doing real timing measurements, e.g. for performance statistics.

This returns the most precise timer we have for short time intervals, but it may tend to drift over the long haul. If more accurate timekeeping is needed over a long period of time, use get_long_time() instead.

void reset(void)

Simultaneously resets both the time and the frame count to zero.

void set_average_frame_rate_interval(double time)

Specifies the interval of time (in seconds) over which get_average_frame_rate() averages the number of frames per second to compute the frame rate. Changing this does not necessarily immediately change the result of get_average_frame_rate(), until this interval of time has elapsed again.

Setting this to zero disables the computation of get_average_frame_rate().

void set_degrade_factor(double degrade_factor)

In degrade mode, sets the ratio by which the performance is degraded. A value of 2.0 causes the clock to be slowed down by a factor of two (reducing performance to 1/2 what would be otherwise).

This has no effect if mode is not M_degrade.

void set_dt(double dt)

In non-real-time mode, sets the number of seconds that should appear to elapse between frames. In forced mode or limited mode, sets our target dt. In normal mode, this has no effect.

Also see set_frame_rate(), which is a different way to specify the same quantity.

void set_frame_count(int frame_count, Thread *current_thread = Thread::get_current_thread())

Resets the number of frames counted to the indicated number. Also see reset(), set_real_time(), and set_frame_time().

void set_frame_rate(double frame_rate)

In non-real-time mode, sets the number of frames per second that we should appear to be running. In forced mode or limited mode, sets our target frame rate. In normal mode, this has no effect.

Also see set_dt(), which is a different way to specify the same quantity.

void set_frame_time(double time, Thread *current_thread = Thread::get_current_thread())

Changes the time as reported for the current frame to the indicated time. Normally, the way to adjust the frame time is via tick(); this function is provided only for occasional special adjustments.

void set_max_dt(double max_dt)

Sets a limit on the value returned by get_dt(). If this value is less than zero, no limit is imposed; otherwise, this is the maximum value that will ever be returned by get_dt(), regardless of how much time has actually elapsed between frames.

This limit is only imposed in real-time mode; in non-real-time mode, the dt is fixed anyway and max_dt is ignored.

This is generally used to guarantee reasonable behavior even in the presence of a very slow or chuggy frame rame.

void set_mode(ClockObject::Mode mode)

Changes the mode of the clock. Normally, the clock is in mode M_normal. In this mode, each call to tick() will set the value returned by get_frame_time() to the current real time; thus, the clock simply reports time advancing.

Other possible modes:

M_non_real_time - the clock ignores real time completely; at each call to tick(), it pretends that exactly dt seconds have elapsed since the last call to tick(). You may set the value of dt with set_dt() or set_frame_rate().

M_limited - the clock will run as fast as it can, as in M_normal, but will not run faster than the rate specified by set_frame_rate(). If the application would run faster than this rate, the clock will slow down the application.

M_integer - the clock will run as fast as it can, but the rate will be constrained to be an integer multiple or divisor of the rate specified by set_frame_rate(). The clock will slow down the application a bit to guarantee this.

M_integer_limited - a combination of M_limited and M_integer; the clock will not run faster than set_frame_rate(), and if it runs slower, it will run at a integer divisor of that rate.

M_forced - the clock forces the application to run at the rate specified by set_frame_rate(). If the application would run faster than this rate, the clock will slow down the application; if the application would run slower than this rate, the clock slows down time so that the application believes it is running at the given rate.

M_degrade - the clock runs at real time, but the application is slowed down by a set factor of its frame rate, specified by set_degrade_factor().

M_slave - the clock does not advance, but relies on the user to call set_frame_time() and/or set_frame_count() each frame.

void set_real_time(double time)

Resets the clock to the indicated time. This changes only the real time of the clock as reported by get_real_time(), but does not immediately change the time reported by get_frame_time()–that will change after the next call to tick(). Also see reset(), set_frame_time(), and set_frame_count().

void sync_frame_time(Thread *current_thread = Thread::get_current_thread())

Resets the frame time to the current real time. This is similar to tick(), except that it does not advance the frame counter and does not affect dt. This is intended to be used in the middle of a particularly long frame to compensate for the time that has already elapsed.

In non-real-time mode, this function has no effect (because in this mode all frames take the same length of time).

void tick(Thread *current_thread = Thread::get_current_thread())

Instructs the clock that a new frame has just begun. In normal, real-time mode, get_frame_time() will henceforth report the time as of this instant as the current start-of-frame time. In non-real-time mode, get_frame_time() will be incremented by the value of dt.