Scheduler ~ Scripting Tool
Version: 1.0

Introduction

How many of you tried creating a parallel process where you put in an amount of frames and then a script call or something else afterwards?
Basically a simply way of doing something after an amount of frames. This is the principle behind the script. To schedule pieces of code to be executed after an arbitrary amount of frames. No making decrementing counters. The scheduler takes care of all that or well most of it. It is still not as simple as using the wait event command.

Script
#==============================================================================
# ** Scheduler
#------------------------------------------------------------------------------
#  This class allows to schedule a proc or method call a given amount of frames
#  into the future with any amount of arguments
#==============================================================================
class Scheduler
  #============================================================================
  # ** Order
  #----------------------------------------------------------------------------
  #  An order is a proc, method or something else which has 'call' as a method,
  #  and the arguments to pass along.
  #============================================================================
  # Create an struct for containing the data
  Order = Struct.new(:callable, :arguments)
  # Extend the class with a call-method which calls the callable with the args
  class Order
    #------------------------------------------------------------------------
    # * Call the callable with the present arguments
    #------------------------------------------------------------------------
    def call
      callable.call(*arguments)
    end
  end
  #============================================================================
  # ** RecurringOrder
  #----------------------------------------------------------------------------
  #  An order which is recurring every specified amount of time until
  #  FalseClass is returned from the call.
  #  Note that arguments remain the same for each call
  #============================================================================
  # Create an struct for containing the data
  RecurringOrder = Struct.new(:callable, :arguments, :frames)
  # Extend the class with a call-method which calls the callable with the args
  class RecurringOrder
    #------------------------------------------------------------------------
    # * Call the callable with the present arguments
    #------------------------------------------------------------------------
    def call
      result = callable.call(*arguments)
      unless result == FalseClass
        Scheduler.schedule_recurring(frames, frames, callable, *arguments)
      end
    end
  end
 
  #============================================================================
  # ** Mapping
  #----------------------------------------------------------------------------
  # Maps an index to an array. Values can be added to these value.
  # Each array starts empty.
  #============================================================================
  class Mapping
    #------------------------------------------------------------------------
    # * Initialization
    #------------------------------------------------------------------------
    def initialize
      @mapping = {}
    end
    #------------------------------------------------------------------------
    # * Add an value to a given index
    #------------------------------------------------------------------------
    def add(index, value)
      @mapping[index] = [] if @mapping[index].nil?
      @mapping[index] << value
    end
    #------------------------------------------------------------------------
    # * Retrieve the list of values mapped to the index
    #------------------------------------------------------------------------
    def get(index)
      return [] if @mapping[index].nil?
      @mapping[index]
    end
    #------------------------------------------------------------------------
    # * Delete the array the index is mapped to. Conceptually it is now empty
    #------------------------------------------------------------------------
    def empty(index)
      @mapping.delete(index)
    end
  end
 
  #--------------------------------------------------------------------------
  # * Initialization
  #--------------------------------------------------------------------------
  def initialize
    # This maps
    @mapping = Mapping.new
    @tick = 0
  end
  #--------------------------------------------------------------------------
  # * Scheduling
  #--------------------------------------------------------------------------
  def schedule(frames, callable, *arguments)
    # Create an order
    order = Order.new(callable, arguments)
    @mapping.add(frames + @tick, order)
  end
  #--------------------------------------------------------------------------
  # * Scheduling
  #--------------------------------------------------------------------------
  def schedule_recurring(frames, frames_to_wait, callable, *arguments)
    # Create an order
    order = RecurringOrder.new(callable, arguments, frames_to_wait)
    @mapping.add(frames + @tick, order)
  end
  #--------------------------------------------------------------------------
  # * Update the scheduler
  #--------------------------------------------------------------------------
  def update
    # Get the orders for the current tick
    orders = @mapping.get(@tick)
    # Delete the mapping's reference to the list of orders
    @mapping.empty(@tick)
    # Call each order
    for order in orders
      order.call
    end
    # Advance the tick (next frame)
    @tick += 1
  end
 
  #--------------------------------------------------------------------------
  # * 'Singleton' principle used although you can easily make
  #   an extra scheduler. (Class method only works for this)
  #--------------------------------------------------------------------------
  @@instance = self.new
  def self.instance
    return @@instance
  end
  ## Class methods point to the equivalent instance methods
  def self.schedule_recurring(*args) instance.schedule_recurring(*args); end
  def self.schedule(*args) instance.schedule(*args); end
  def self.update(*args) instance.update(*args); end
end

Here is a binding if you want the scheduler to work for every frame. Basically for each Graphic.update the scheduler is updated.
It doesn't matter whether you are in a menu, title screen, battle. As long as Graphic.update is called so is the scheduler. (The main scheduler)

module Graphics
  class << self
    unless self.method_defined?(:scheduler_update)
      alias :scheduler_update :update
    end
    def update(*args)
      scheduler_update(*args)
      Scheduler.update
    end
  end
end

Instructions

Semi-big and evil instructions
You can schedule in two ways.
You can do a one-time schedule which works like this: (Using the class method)

Scheduler.schedule(frames, callable, *arguments)
# Here's an example
Scheduler.schedule(65, Proc.new {|x,y| p x,y}, "A string", 42)

The 65 means that the proc will be called after 65 frames. (Or 65 ticks to be more precise. 1 update = 1 tick usually)
After 65 ticks the proc {|x,y| p x,y} will be called with the arguments x = "A string" and y = 42. (The *arguments means any number of arguments. This can also be no arguments at all)
The Scheduler uses duck typing and assumes that anything which has the .call method works properly in the context. I imagine procs and methods to be the most commonly used.

The next is that you can schedule a recurring call which works like this: (Using the class method)

Scheduler.schedule_recurring(frames, frames_to_wait, callable, *arguments)
# Here's an example
Scheduler.schedule_recurring(65, 30, Proc.new {|x,y| p x,y}, "A string", 42)

The arguments is the same as for the one-time with the addition of the frames_to_wait argument.
This specifies that after the first 65 ticks each recurring call will happen after 30 ticks.
This will continue until the callable returns FalseClass. (Mind you it's false.class and not false)

Now you have to update the schedule every frame or it won't schedule properly.
Here is a binding where the scheduler updates every time the Graphics module updates. (Made for XP. I am unsure whether this part works in VX)

module Graphics
  class << self
    unless self.method_defined?(:scheduler_update)
      alias :scheduler_update :update
    end
    def update(*args)
      scheduler_update(*args)
      Scheduler.update
    end
  end
end

Note that the class methods only work for one scheduler. I believe this should be the generally working Scheduler.


Compatibility

The Scheduler alone use only Ruby and could easily be placed in a Ruby if one wanted that.
It is highly unlikely that you will encounter any compatibility issues with the backbone alone since it is independent from RGSS/2 library.

On the other side there could potentially be problems with the bindings which makes use of the scheduler so it actually does something in game.
Currently there is only the Graphics.update binding which makes compatibility issues very unlikely.

Future Work
- Explicitly exit/stop a scheduler. The scheduled items can then be discard, executed or maybe something else.
- Error handling. (This may be an external. I.e. not embedded in the core)
- Documentation

Credits and Thanks

Credits goes to Zeriab for creating the system

I would like to thank everyone using their time to try and use my system.
I would like to thank everyone reading this topic.

Thanks.

Author's Notes

I would be delighted if you report any bug, errors or issues you find.
In fact I would be delighted if you took the time and replied even if you have nothing to report.
Suggestions are more than welcome.

Note that I will release a demo which shows a couple of ways of using this script.
Note also that I will always make a post when I have an update. (Small stuff like typos excluded)

And finally: ENJOY!

- Zeriab
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