Class: RedBird::Timer

Inherits:
Data
  • Object
show all
Defined in:
ext/red_bird/timer.c,
ext/red_bird/timer.c

Overview

A Timer controls the speed of execution of a frame; it prevents that a frame run too quickly and give you compensation when a frame runs too slow.

When creating a new instance, you must define the maximum frame rate that you want; then, you should call #tick at every frame to get a delta time. The delta time is proportional to the frame rate defined during the creation of the instance or is higher when the last frame was slower than expected.

Author:

  • Frederico Linhares

Instance Method Summary collapse

Constructor Details

#initialize(max_fps) ⇒ Object

Parameters:

  • max_fps (Integer) —

    the maximum of frames to be rendered per second.

Author:

  • Frederico Linhares



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# File 'ext/red_bird/timer.c', line 64

VALUE
bird_cTimer_initialize(VALUE self, VALUE max_fps)
{
  struct bird_timer_data *ptr;

  if(!engine_initialized)
    rb_raise(rb_eRuntimeError, "%s",
             "can not create a RedBird::Timer instance before "
             "RedBird::Engine is started");

  RB_INTEGER_TYPE_P(max_fps);

  TypedData_Get_Struct(self, struct bird_timer_data, &bird_timer_type, ptr);
  ptr->max_frame_duration_ms = 1000 / NUM2INT(max_fps);
  ptr->max_frame_duration_sec = ptr->max_frame_duration_ms/1000.0;
  ptr->frame_start = SDL_GetTicks();

  return self;
}

Instance Method Details

#tick ⇒ Float

Every time you call this method, it compares the current time with the last time it was called; if the amount of time is inferior to the frame duration, it waits to ensure the frame has the exact duration expected; otherwise, it returns instantly and gives you a delta value that compensates for the extra duration of the last frame.

Returns:

  • (Float) —

    represents the amount of time between this frame and the last frame, the higher, the higher amount of time has passed.

Author:

  • Frederico Linhares



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# File 'ext/red_bird/timer.c', line 95

VALUE
bird_cTimer_tick(VALUE self)
{
  struct bird_timer_data *ptr;
  Uint32 frame_stop;
  Uint32 frame_duration;
  VALUE delta;

  TypedData_Get_Struct(self, struct bird_timer_data, &bird_timer_type, ptr);

  frame_stop = SDL_GetTicks();
  frame_duration = frame_stop - ptr->frame_start;

  // If frame take less time than maximum allowed.
  if(ptr->max_frame_duration_ms > frame_duration)
  {
    SDL_Delay(ptr->max_frame_duration_ms - frame_duration);
    delta = rb_float_new(ptr->max_frame_duration_sec);
  }
  // If frame take too long time.
  else
  {
    // SDL_GetTicks return time im miliseconds, so I need to divide by 1000 to
    // get the time in seconds.
    delta = rb_float_new((double)frame_duration/1000.0);
  }

  ptr->frame_start = frame_stop;

  return delta;
}