Contents

# The Nature of Code
# Daniel Shiffman
# http://natureofcode.com
require 'forwardable'

# Series of Particles connected with distance joints
class Pair
  extend Forwardable
  def_delegators(:@app, :box2d, :stroke, :line, :stroke_weight)
  attr_reader :p1, :p2, :len
  # Chain constructor
  def initialize(x, y)
    @app = $app
    @len = 32
    @p1 = Particle.new(x, y)
    @p2 = Particle.new(x + rand(-1..1.0), y + rand(-1..1.0))
    djd = DistanceJointDef.new
    # Connection between previous particle and this one
    djd.bodyA = p1.body
    djd.bodyB = p2.body
    # Equilibrium length
    djd.length = box2d.scale_to_world(len)    
    # These properties affect how springy the joint is 
    djd.frequencyHz = 3     # Try a value less than 5 (0 for no elasticity)
    djd.dampingRatio = 0.1  # Ranges between 0 and 1 (1 for no springiness)
    # Make the joint.  Note we aren't storing a reference to the joint ourselves anywhere!
    # We might need to someday, but for now it's ok
    box2d.world.create_joint(djd)
  end

  def display
    pos1 = box2d.body_coord(p1.body)
    pos2 = box2d.body_coord(p2.body)
    stroke(0)
    stroke_weight(2)
    line(pos1.x, pos1.y, pos2.x, pos2.y)
    p1.display
    p2.display
  end
end

Version data entries

2 entries across 2 versions & 1 rubygems

Version	Path
pbox2d-0.4.1-java	examples/distance_joint/pair.rb
pbox2d-0.4.0-java	examples/distance_joint/pair.rb