Class Rubygame::Clock
In: lib/rubygame/clock.rb
Parent: Object

Clock provides class methods for tracking running time and delaying execution of the program for specified time periods. This is used to provide a consistent framerate, prevent the program from using all the processor time, etc.

Clock also provides instance methods to make it convenient to monitor and limit application framerate. See tick.

An in-depth tutorial on using Clock is available. See doc/managing_framerate.rdoc in the Rubygame source distribution or in the online documentation.

Methods

Attributes

granularity  [RW]  Granularity used for framerate limiting delays in tick. You can calibrate this easily with calibrate. See also tick and Clock.delay. (Non-negative integer. Default: 12.)
nice  [RW]  Whether to try to let other ruby threads run during framerate limiting delays in tick. See tick and Clock.delay. (true or false. Default: false.)
start  [R]  The runtime when the Clock was initialized.
ticks  [R]  The number of times tick has been called.

Public Class methods

time:The target delay time, in milliseconds. (Non-negative integer. Required.)
gran:The assumed granularity (in ms) of the system clock. (Non-negative integer. Optional. Default: 12.)
nice:If true, try to let other ruby threads run during the delay. (true or false. Optional. Default: false.)
Returns:The actual delay time, in milliseconds.

Pause the program for time milliseconds. This function is more accurate than Clock.wait, but uses slightly more CPU time. Both this function and Clock.wait can be used to slow down the framerate so that the application doesn’t use too much CPU time. See also Clock#tick for a good and easy way to limit the framerate.

This function uses “busy waiting” during the last part of the delay, for increased accuracy. The value of gran affects how many milliseconds of the delay are spent in busy waiting, and thus how much CPU it uses. A smaller gran value uses less CPU, but if it’s smaller than the true system granularity, this function may delay a few milliseconds too long. The default value (12ms) is very safe, but a value of approximately 5ms would give a better balance between accuracy and CPU usage on most modern computers. A granularity of 0ms makes this method act the same as Clock.wait (i.e. no busy waiting at all, very low CPU usage).

If nice is true, this function will try to allow other ruby threads to run during this function. Otherwise, other ruby threads will probably also be paused. Setting nice to true is only useful if your application is multithreaded. It’s safe (but pointless) to use this feature for single threaded applications.

The Rubygame timer system will be initialized when you call this function, if it has not been already. See Clock.runtime.

[Source]

# File lib/rubygame/clock.rb, line 83
      def delay( time, gran=12, nice=false )
        _init_sdl_timer
        time = 0 if time < 0
        gran = 0 if gran < 0
        _accurate_delay( time, gran, nice )
      end

Create a new Clock instance.

[Source]

# File lib/rubygame/clock.rb, line 227
    def initialize()
      @start = self.class.runtime()
      @last_tick = nil
      @ticks = 0

      @target_frametime = nil

      # Frametime samples for framerate calculation
      @samples = []
      @max_samples = 20

      @granularity = 12
      @nice = false

      # Should #tick return a ClockTicked event?
      @tick_events = false

      # Cache for past tick events with specific ms values
      @tick_cache = {}

      yield self if block_given?
    end

Return the number of milliseconds since the Rubygame timer system was initialized.

The Rubygame timer system will be initialized when you call this function, if it has not been already.

[Source]

# File lib/rubygame/clock.rb, line 131
      def runtime
        SDL.GetTicks().to_i
      end
time:The target wait time, in milliseconds. (Non-negative Integer. Required.)
nice:If true, try to let other ruby threads run during the delay. (true or false. Optional.)
Returns:The actual wait time, in milliseconds.

Pause the program for approximately time milliseconds. Both this function and Clock.delay can be used to slow down the framerate so that the application doesn’t use too much CPU time. See also Clock#tick for a good and easy way to limit the framerate.

The accuracy of this function depends on processor scheduling, which varies with operating system and hardware. The actual delay time may be up to 10ms longer than time. If you need more accuracy use Clock.delay, which is more accurate but uses slightly more CPU time.

If nice is true, this function will try to allow other ruby threads to run during this function. Otherwise, other ruby threads will probably also be paused. Setting nice to true is only useful if your application is multithreaded. It’s safe (but pointless) to use this feature for single threaded applications.

The Rubygame timer system will be initialized when you call this function, if it has not been already. See Clock.runtime.

[Source]

# File lib/rubygame/clock.rb, line 118
      def wait( time, nice=false )
        _init_sdl_timer
        time = 0 if time < 0
        _threaded_delay( time, nice )
      end

Public Instance methods

Calibrate some Clock settings to match the current computer. This improves efficiency and minimizes CPU usage without reducing accuracy.

As of Rubygame 2.5, this method calibrates @granularity. See tick and Clock.delay for more information about the effect of setting granularity. In future versions of Rubygame, this method may also calibrate additional Clock attributes.

By default, the calibration takes a maximum of 0.5 seconds to complete. You can specify a different maximum length by passing a different value for max_time. In future versions of Rubygame, calibration may take less than max_time, but will not take more. Also, the default max_time may be lowered in future versions, but will not be raised.

You usually only need to call this once, after you create the Clock instance at the start of your application. You should not run any other ruby threads at the same time, as doing so will skew the calibration.

[Source]

# File lib/rubygame/clock.rb, line 280
    def calibrate( max_time = 0.5 )
      samples = []

      end_time = Time.now + max_time

      while( Time.now < end_time )
        t = Time.now
        sleep 0.01
        samples << (Time.now - t - 0.01)
      end

      average = samples.inject{|sum,n| sum + n} / samples.length

      # convert to ms, add some padding
      gran = (average * 1000).to_i + 1

      @granularity = gran

      return nil
    end

Enable tick events, so that tick will return a ClockTicked instance instead of a number of milliseconds.

This option is available starting in Rubygame 2.5, and will become the default in Rubygame 3.0.

[Source]

# File lib/rubygame/clock.rb, line 308
    def enable_tick_events
      @tick_events = true
    end

Return the actual framerate (frames per second) recorded by the Clock. See tick.

[Source]

# File lib/rubygame/clock.rb, line 387
    def framerate
      sum = @samples.inject(0){|sum, n| sum + n}
      if sum == 0
        return 0.0
      else
        1000.0 * @samples.length / sum
      end
    end

Return the actual frametime (milliseconds per frame) recorded by the Clock. See tick.

[Source]

# File lib/rubygame/clock.rb, line 403
    def frametime
      @samples.inject(0){|sum, n| sum + n} / (@samples.length)
    rescue ZeroDivisionError
      0.0
    end

Returns time in milliseconds since this Clock instance was created.

[Source]

# File lib/rubygame/clock.rb, line 376
    def lifetime
      self.class.runtime() - @start
    end

Returns the current target framerate (frames/second), or nil if there is no target.

This is another to access target_frametime. Same as: 1000.0 / target_frametime

[Source]

# File lib/rubygame/clock.rb, line 342
    def target_framerate
      if @target_frametime
        1000.0 / @target_frametime
      else
        nil
      end
    rescue ZeroDivisionError
      return nil
    end

Sets the target number of frames per second to framerate. If framerate is nil, the target is unset, and tick will no longer apply any delay.

This is another way to access target_frametime. Same as: target_frametime = 1000.0 / framerate

[Source]

# File lib/rubygame/clock.rb, line 360
    def target_framerate=( framerate )
      if framerate
        @target_frametime = 1000.0 / framerate
      else
        @target_frametime = nil
      end
    rescue ZeroDivisionError
      @target_frametime = nil
    end

Returns the current target frametime (milliseconds/frame), or nil if there is no target.

This is another way to access target_framerate. Same as: 1000.0 / target_framerate

[Source]

# File lib/rubygame/clock.rb, line 319
    def target_frametime
      @target_frametime
    end

Sets the target milliseconds per frame to frametime. If frametime is nil, the target is unset, and tick will no longer apply any delay.

This is another way to access target_framerate. Same as: target_framerate = 1000.0 / frametime

[Source]

# File lib/rubygame/clock.rb, line 331
    def target_frametime=( frametime )
      @target_frametime = frametime
    end

Returns the number of milliseconds since you last called this method. Or, if you have called enable_tick_events, this returns a ClockTicked event representing the time since you last called this method. (ClockTicked was added in Rubygame 2.5, and will become the default and only option in Rubygame 3.0.)

You must call this method once per frame (i.e. per iteration of your main loop) if you want to use the framerate monitoring and/or framerate limiting features.

Framerate monitoring allows you to check the framerate (frames per second) or frametime (milliseconds per frame) of your game.

Framerate limiting allows you to prevent the application from running too fast (and using 100% of processor time) by pausing the program very briefly each frame. The pause duration is calculated each frame to maintain a stable framerate.

Framerate limiting is only enabled if you have set the target_framerate= or target_frametime=. If you have done that, this method will automatically perform the delay each time you call it.

There are two other attributes which affect framerate limiting, granularity and nice. These are passed as parameters to Clock.delay for the brief pause each frame. See Clock.delay for the effects of those parameters on CPU usage and threading.

(Please note that no effort is made to correct a framerate which is slower than the target framerate. Clock can’t make your code run faster, only slow it down if it is running too fast.)

[Source]

# File lib/rubygame/clock.rb, line 442
    def tick()

      # how long since the last tick?
      passed = 0
      if @last_tick
        passed += self.class.runtime() - @last_tick
      end

      if @target_frametime
        extra = @target_frametime - passed
        if( extra > 0 )
          passed += self.class.delay( extra, @granularity, @nice )
        end
      end

      if @tick_events
        return (@tick_cache[passed] or 
                 (@tick_cache[passed] =
                  Rubygame::Events::ClockTicked.new( passed ) ))
      else
        return passed
      end

    ensure
      @last_tick = self.class.runtime()
      @ticks += 1

      # Save the frametime for framerate calculation
      @samples.push(passed)
      @samples.shift if @samples.length > @max_samples
    end

[Validate]