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predator/prey simulation

import random
import time
def chase():

  # Create an amphitheater in which our turtles will fight to the death
  amphitheater = makeWorld(960, 720)

  # Create two turtles: a predator and its prey
  predator = makeTurtle(amphitheater)
  prey = makeTurtle(amphitheater)

  # The predator's and prey's initial speeds
  predSpeed = 40
  preySpeed = predSpeed - 10

  # Position the turtles in their starting positions.
  # The predator is aiming at the prey; the prey is pointing South-East.
  penUp(predator)
  penUp(prey)
  x1 = random.choice(range(0, amphitheater.getWidth()/4))
  y1 = random.choice(range(0, amphitheater.getHeight()/4))
  x2 = amphitheater.getWidth()/2
  y2 = amphitheater.getHeight()/2
  moveTo(predator, x1, y1)
  moveTo(prey, x2, y2)
  turnToFace(predator, x2, y2)
  turnToFace(prey, amphitheater.getWidth(), amphitheater.getHeight())
  penDown(predator)
  penDown(prey)

  # Have the predator chase the prey and the prey run away until the
  # predator has closed to within tooth distance.
  while distanceBetween(predator, prey) > 5 and predSpeed > 0:

    # The predator aims at where the prey is, not where it is moving to.
    # But if it is fast enough, it won't keep going round in a circle.
    turnToFace(predator, prey.getXPos(), prey.getYPos())

    # The prey panics and keeps changing direction.
    evasiveAngle = random.choice(range(-75, 75))
    turn(prey, evasiveAngle)
    forward(prey, preySpeed)

    # Pause so that we can watch what happens at leisure.
    time.sleep(0.25)

    # We need to stop the predator overshooting.
    # See what happens if you take this out.
    closingDistance = int(min(distanceBetween(predator, prey), int(predSpeed)))

    # Close in on the victim
    forward(predator, closingDistance)

    # Pause so that we can watch what happens at leisure.
    time.sleep(0.25)

    if predSpeed >= 0:
      predSpeed = predSpeed - 0.25


# Compute the Euclidean distance between turtles. Very like the distance between
# colors, except that they have three dimensions (RGB). Turtles live in a
# two-dimensional plane.
def distanceBetween(turtle1, turtle2):
  x1 = turtle1.getXPos()
  x2 = turtle2.getXPos()
  y1 = turtle1.getYPos()
  y2 = turtle2.getYPos()
  dist = math.sqrt((x1-x2)**2 + (y1-y2)**2)
  return dist
  

def sickScreenSaver():
  while 1:
    chase()
    time.sleep(2.0)

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• Slides and Code- Spring 2008 last edited on 23 April 2008 at 11:00 am by lawn-128-61-23-153.lawn.gatech.edu