Shadow effect in Gamebox

demo_stage.rb

define_behavior :faded do
  requires :timer_manager
  setup do
    actor.has_attributes shadows: [], shadows_to_render: opts[:shadows_to_render]

    timer_manager.add_timer timer_name, 100 do
      new_shadow = {x: actor.x, y: actor.y} 
      actor.shadows << new_shadow
      actor.shadows.shift if actor.shadows.size > actor.shadows_to_render
    end
    reacts_with :remove
  end

  helpers do
    def timer_name
      "actor_shadow_#{actor.object_id}"
    end
    def remove
      timer_manager.remove_timer timer_name
    end
  end
end

define_actor :player do
  has_behaviors do
    positioned
    faded shadows_to_render: 10
  end

  view do
    draw do |target, x_off, y_off, z|

      c = Color::RED
      scale = 255.0/actor.shadows.size
      actor.shadows.each.with_index do |s, i|
        x = s[:x] + x_off
        y = s[:y] + y_off

        alpha = i * scale
        shadow_color = [c.red,c.green,c.blue,alpha]

        target.draw_box x,y, x+20, y+20, shadow_color, 1
      end

      # draw current
      x = actor.x + x_off
      y = actor.y + y_off
      target.draw_box x,y, x+20, y+20, Color::RED, 1

    end
  end
end
define_stage :demo do
  requires :tween_manager

  curtain_up do
    @player = spawn :player, x: 10, y:30
    tween = tween_manager.tween_properties @player, {x: 600, y:750}, 6_000, Tween::Sine::InOut
  end
end