old_contents: """
  Multiple Particle Systems
  by Daniel Shiffman.
  
  Click the mouse to generate a burst of particles
  at mouse location.
  
  Each burst is one instance of a particle system
  with Particles and CrazyParticles (a subclass of Particle).
  Note use of Inheritance and Polymorphism here.
  """
  
  from crazy_particle import CrazyParticle
  from particle import Particle
  from particle_system import ParticleSystem
  
  systems = None
  
  def setup():
      size(640, 360)
      systems = []
  
  
  def draw():
      background(0)
      for ps in systems:
          ps.run()
          ps.addParticle()
  
      if not systems:
          fill(255)
          textAlign(CENTER)
          text("click mouse to add particle systems", width / 2, height / 2)
  
  
  def mousePressed():
      systems.append(ParticleSystem(1, PVector(mouseX, mouseY)))
  
  
new_contents: """
  Multiple Particle Systems
  by Daniel Shiffman.
  
  Click the mouse to generate a burst of particles
  at mouse location.
  
  Each burst is one instance of a particle system
  with Particles and CrazyParticles (a subclass of Particle).
  Note use of Inheritance and Polymorphism here.
  """
  
  from crazy_particle import CrazyParticle
  from particle import Particle
  from particle_system import ParticleSystem
  
  systems = None
  
  def setup():
      global systems
      size(640, 360)
      systems = []
  
  
  def draw():
      background(0)
      for ps in systems:
          ps.run()
          ps.addParticle()
  
      if not systems:
          fill(255)
          textAlign(CENTER)
          text("click mouse to add particle systems", width / 2, height / 2)
  
  
  def mousePressed():
      systems.append(ParticleSystem(1, PVector(mouseX, mouseY)))
  
subject: Update MultipleParticleSystems.pyde