processing.rb

require 'java'
require 'core'
include_class Java::processing.core.PApplet

def run!(acls)
  runswing! acls
end

def runswing!(acls)
  jFrame = Java::javax.swing.JFrame
  frame = jFrame.new acls.name
  applet = acls.new
  frame.content_pane.add applet
  frame.default_close_operation = jFrame::EXIT_ON_CLOSE
  applet.init
  frame.pack
  frame.visible = true
end

class Closer < Java::java.awt.event.WindowAdapter
  def windowClosing(e)
    exit 0
  end
end

def runawk!(acls)
  frame = Java::java.awt.Frame::new
  applet = acls.new
  frame.setResizable false
  applet.frame = frame
  frame.setLayout nil
  frame.add applet
  frame.pack
  applet.init

  insets = frame.getInsets
  winW = [applet.width , PApplet::MIN_WINDOW_WIDTH ].max + insets.left + insets.right
  winH = [applet.height, PApplet::MIN_WINDOW_HEIGHT].max + insets.top + insets.bottom
  frame.setSize winW, winH
  usableWinH = winH - insets.top - insets.bottom
  applet.setBounds((winW - applet.width)/2 , insets.top + (usableWinH - applet.height)/2 , applet.width, applet.height)

  frame.addWindowListener Closer.new
  applet.setupFrameResizeListener

  frame.setVisible true
  applet.requestFocus
end

slingshot.rb

$gravity = 200.0
$fps = 24

require 'processing'

class Planet
    attr_accessor :mass, :r, :pos
    def initialize(parent)
        @p = parent
        @mass = rand(504) + 8
        @r = @mass**(1.0/3.0) * 12.5
        @pos = rand(760) + 20, rand(560) + 20
    end

    def draw(alpha = 11)
        @p.fill 99, alpha+11
        @p.stroke 66, alpha
        x, y = @pos
        @p.ellipse x, y, @r, @r
    end
end

class Particle
    attr_accessor :pos, :speed, :angle, :v, :last, :color
    def initialize(parent, pos, angle, color = 111, speed = 100)
        @p = parent
        @last = [pos]*6
        @pos = pos
        @speed = speed
        @angle = angle
        @color = color
        @v = 0.1 * speed * Math.sin(angle), -0.1 * speed * Math.cos(angle)
    end

    def update(planets)
        @last.shift
        @last += [@pos]
        pos = @pos
        planets.each { |planet|
            d = (pos[0] - planet.pos[0])**2 + (pos[1] - planet.pos[1])**2
            d *= d if Math.sqrt(d) < planet.r
            a = $gravity * planet.mass * (pos[0] - planet.pos[0]) / (d * Math.sqrt(d)),
                $gravity * planet.mass * (pos[1] - planet.pos[1]) / (d * Math.sqrt(d))
            @v = (@v[0] - a[0])*0.99,
                 (@v[1] - a[1])*0.99
        }
        r = Math.sqrt(@v[0]**2+@v[1]**2)
        @v = @v[0]*0.3, @v[1]*0.3 if r > 100
        @v = @v[0]*3.0, @v[1]*3.0 if r < 10
        @pos = [ pos[0]+@v[0], pos[1]+@v[1] ]
    end

    def draw
        @p.noFill
        #@p.fill 222, 5
        @p.stroke @color

        (0..(rand(4)+2)).each {
            @p.curveTightness rand(70)/10.0-3.5
            @p.beginShape
                @last.each { |x, y| @p.curveVertex x, y }
                @p.curveVertex *@pos
            @p.endShape
        }

    end
end

class Slingshot < PApplet

  def setup
    size 800, 600
    smooth
    frameRate $fps
    @planets, @particles, @i, @n = [], [], 0, 0
    (0..(rand(7)+1)).each { @planets += [Planet.new self]}
    (0..30).each { @particles += [Particle.new(self, [10,300],rand(360),color(111,11))]}
    (0..30).each { @particles += [Particle.new(self, [790,300],rand(360),color(111,11))]}

    background 0
    @planets.each { |planet| planet.draw }
  end

  def draw
    @i += 1
    filter BLUR   if 0 == @i % ($fps/2)
    filter DILATE if 0 == @i % $fps
    if 0 == @i % ($fps*2)
        filter ERODE
        @n += 1
        @i = 0
    end
    if 5 == @n
        @planets, @particles, @n = [], [], 0
        (0..(rand(7)+1)).each { @planets += [Planet.new self]}
        (0..30).each { @particles += [Particle.new(self, [10,300],rand(360),color(111,11))]}
        (0..30).each { @particles += [Particle.new(self, [790,300],rand(360),color(111,11))]}
        #background 11, 1
        filter ERODE
        filter ERODE
        @planets.each { |planet| planet.draw 0 }
    end
    #background 11, 1
    #@planets.each { |planet| planet.draw }
    @particles.each { |plarticle| plarticle.update @planets }
    @particles.each { |plarticle| plarticle.draw }
  end

end

run! Slingshot