Fruit Flies

fruit_flies.rb

# video https://twitter.com/josh_cheek/status/833115369267150848
require "graphics"

class FruitFlies < Graphics::Simulation
  CLEAR_COLOR = [10, 21, 36]

  def initialize
    super 600, 350, 24
    @points = 400.times.map { rand_point }
    @delayed_draw = []
    color.default_proc = -> h, k { k }  # so we don't have to rely on named colours
  end

  def draw(ticks)
    clear

    # randomly swap out some of the points so the lines change across frames
    rand(15).times do
      idx = rand(@points.length)
      @points[idx] = rand_point
    end

    end_clip   = (@points.length*0.3).to_i
    num_frames = @points.length-2*end_clip
    color      = [rand(255), rand(255), rand(255)]
    if ticks % 5 == 1
      points = @points
      end_clip.times { points = percentages_between points, 0.5 }
      num_frames.times do |i|
        points      = percentages_between points, 0.5
        path_points = points.take(4)
        dim_amt     = 1-Math.sin(Math::PI*i/num_frames)
        crnt_clr    = dim(color, dim_amt)

        (@delayed_draw[i] ||= []) << [dim_amt, lambda {
          draw_lines_between path_points, crnt_clr
          draw_lines_between path_points.map { |x, y| [x+1, y] }, crnt_clr
          draw_lines_between path_points.map { |x, y| [x, y+1] }, crnt_clr
          draw_lines_between path_points.map { |x, y| [x+2, y] }, crnt_clr
          draw_lines_between path_points.map { |x, y| [x, y+2] }, crnt_clr
          circle *path_points.last, 5, dim(white, dim_amt), true
        }]
      end
    end

    (@delayed_draw.shift||[])
      .sort_by { |dim, _| dim }      # draw dim ones first so they are in the bg
      .each { |_, draw| draw.call }  # draw the line
  end

  def mix((r1, g1, b1), (r2, g2, b2))
    [(r1+r2)/2, (g1+g2)/2, (b1+b2)/2]
  end

  def white
    @white ||= [255, 255, 255]
  end

  def dim((r, g, b), percent)
    end_r, end_g, end_b = CLEAR_COLOR
    [ r + (end_r-r)*percent,
      g + (end_g-g)*percent,
      b + (end_b-b)*percent,
    ]
  end

  def draw_lines_between(points, color)
    points.each_cons 2 do |(x1, y1), (x2, y2)|
      line x1, y1, x2, y2, color
    end
  end

  # feels like if I think about calculus for a little bit, I might be able to
  # come up with an equation for htis so that we don't have to repeatedly invoke it
  def percentages_between(points, percent)
    points.each_cons(2).map do |(x1, y1), (x2, y2)|
      [x1+(x2-x1)*percent, y1+(y2-y1)*percent]
    end
  end

  def rand_point
    [rand(5*w)-2*w, rand(5*h)-2*h]
  end
end

FruitFlies.new.run