friction.rb

panel.rb

module HackOS
  class Panel < Hokusai::Block
    template <<~EOF
    [template]
      clipped {
        @tap="on_tapdown"
        @drag="on_taphold"
        @taphold="on_taphold"
        @swipe="on_swipe"
        @taprelease="on_taprelease"
        :autoclip="autoclip" 
        :offset="offset"
      }
        dynamic { @size_updated="set_size" }
          slot
    EOF

    uses(
      clipped: Hokusai::Blocks::Clipped,
      dynamic: Hokusai::Blocks::Dynamic,
    )

    computed :autoclip, default: true
    computed :friction, default: 0.96, convert: proc(&:to_f)

    attr_accessor :top, :offset, :clipped_content_height, :panel_height

    def on_tapdown(event)
      @tap = event.pos.y
      @timer ||= Timer.new # for swipes
      @velocity = nil
    end

    def on_taprelease(event)
      @tap = nil
      @delta = nil
      @timer = nil
    end

    # move the screen according to hold pos.y
    def on_taphold(event)
      @delta = (@tap - event.pos.y.to_f)
      @tap = event.pos.y
      @timer.restart

      clamp_offset(@delta)
    end

    def on_swipe(event)
      if event.swipe_direction == :up || event.swipe_direction == :down
        @velocity = (@delta / (@timer.elapsed * 1000))
      end
    end

    def clamp_offset(delta)
      if offset + delta < panel_top
        self.offset = panel_top
      elsif offset + delta > content_height - panel_height
        self.offset = content_height - panel_height
      else
        self.offset += delta
      end
    end

    def momentum
      @velocity *= friction;
      if @velocity.abs < 0.01
        @velocity = nil
        
        return
      end
      
      offsetdelta = @velocity * 16
      clamp_offset(offsetdelta)
    end

    def set_size(_, height)
      if panel_height != clipped_content_height || clipped_content_height.zero?
        self.clipped_content_height = height
      end
    end

    def content_height
      clipped_content_height
    end

    def panel_top
      top || 0.0
    end

    def set_size(_, height)
      if panel_height != clipped_content_height || clipped_content_height.zero?
        self.clipped_content_height = height
      end
    end

    def initialize(**args)
      @top = nil
      @offset = 0
      @clipped_content_height = 0
      @panel_height = 0

      @velocity = 0.0 # between 0 and 1
      super
    end

    def render(canvas)
      self.top ||= canvas.y
      self.panel_height = canvas.height
      
      if @velocity
        momentum
      end

      @timer&.next

      yield canvas
    end
  end
end