Heartbeat of SketchUp animation pumping Ruby script

The heartbeat is a timer that ticks regularly. This tick runs Ruby script block, which increments position or angle of SketchUp's instance toward target. Refer below code snippet for a timer usage and block execution by the timer tick.

	def run( model, period )
	timer_id = UI.start_timer( period, true) do # for every beat of lub dub lub dub, run below block
	@actions.delete_if do |a|
	a.tick( period ) # move around instance
	a.arrived? # remove if instance arrived at target
	end
	model.active_view.invalidate # update scene
	if @actions.empty? then
	UI.stop_timer timer_id # rest in peace if nothing left
	end
	end
	end

view raw motion_movement_run.rb hosted with ❤ by GitHub

In the code, I said the heart beats at precise interval of 'period' and you can say that I should somehow replace the timer with atom clock to get that behaviour. Well, we may meet in the middle by measuring duration; We can't make consistent period but we can get elapsed time between consequent timer calls. Refer below code.

	attr_reader :last_time
	def initialize
	@last_time = 0.0
	end
	def run( model, period )
	timer_id = UI.start_timer( period, true) {
	if @last_time == 0.0
	@last_time = Time.now.to_f
	elapsed_time = period
	else
	current_time = Time.now.to_f
	elapsed_time = current_time - @last_time
	@last_time = current_time
	end
	@actions.delete_if do |a|
	a.tick( elapsed_time )
	a.arrived?
	end
	# snip snip
	end

view raw update_motion_movement.rb hosted with ❤ by GitHub

Below is code for object translation. 'entity.transform!' updates the position. This change will be shown by model.active_view.update - search up above code.

Updating position in the middle is easy as it is moving in constant speed. Difficulty lies at the boundaries - reminding me of studying differential equations, asking for great care on boundary condition at all times. In here I have to figure out where and when to stop. I am just checking the remaining distance to the target position in here.

	class Translation < Action
	attr_accessor :target, :velocity, :speed
	def tick( duration )
	return if arrived?
	ds = @speed * duration # distance to cover in this tick
	d = (@target - @entity.transformation.origin).normalize # direction vector in unit distance
	d.x, d.y, d.z = d.x*ds, d.y*ds, d.z*ds # distance vector toward target
	s = @entity.transformation.origin # start position
	e = s + d # end position
	dt = s.distance @target # distance between start and end
	if ds >= dt # if reached the target
	d = @target - s; # update distance vector with remaining distance
	@is_arrived = true
	end
	@entity.transform! Geom::Transformation.new( d ) # update position of SketchUp instance
	...
	end
	end

view raw motion_translation_tick.rb hosted with ❤ by GitHub

This simple approach - constant speed - makes unrealistic movements at the boundaries. It starts and stops in infinite acceleration. Better simulation should involve smooth change at ends.

Reference : Animate Yo' Cheese