refactor jbox2d examples

Author: monkstone

samples/external_library/ruby_gem/jbox2d/bumpy_surface_noise.rb

@@ -37,5 +37,5 @@ def draw
   particles.reject!(&:done)
   # Just drawing the framerate to see how many particles it can handle
   fill(0)
-  text("framerate: #{frame_rate.to_i}", 12, 16)
+  text(format('framerate: %d', frame_rate), 12, 16)
 end

samples/external_library/ruby_gem/jbox2d/collision_listening.rb

@@ -1,23 +1,26 @@
 require 'pbox2d'
+require 'forwardable'
 require_relative 'lib/custom_listener'
 require_relative 'lib/particle'
 require_relative 'lib/boundary'
 
 attr_reader :box2d, :particles, :wall
 
+Vect = Struct.new(:x, :y)
+
 def setup
   size 400, 400
   @box2d = Box2D.new(self)
   box2d.create_world
   box2d.add_listener(CustomListener.new)
   @particles = []
-  @wall = Boundary.new(box2d, width / 2, height - 5, width, 10)
+  @wall = Boundary.new(box2d, Vect.new(width / 2, height - 5), Vect.new(width, 10))
 end
 
 def draw
   background(255)
-  particles << Particle.new(box2d, rand(width), 20, rand(4..8)) if rand < 0.1
-  particles.each{ |p| p.display(self) }
+  particles << Particle.new(self, rand(width), 20, rand(4..8)) if rand < 0.1
+  particles.each(&:display)
   particles.reject!(&:done)
-  wall.display(self)
-end
+  wall.display
+end

samples/external_library/ruby_gem/jbox2d/lib/box.rb

@@ -1,5 +1,5 @@
 # A Box class, note how to access class ParticleGroupDef in jruby
-# which is currently not on an included path for pbox2d
+# which is imported into PB module (not in global namespace)
 class Box
   attr_accessor :pg
   def initialize(b2d, x, y)
@@ -8,8 +8,8 @@ def initialize(b2d, x, y)
     shape = PolygonShape.new
     pos = b2d.processing_to_world(x, y)
     shape.setAsBox(w, h, pos, 0)
-    pd = Java::OrgJbox2dParticle::ParticleGroupDef.new
+    pd = PB::ParticleGroupDef.new
     pd.shape = shape
     @pg = b2d.world.create_particle_group(pd)
   end
-end
+end

samples/external_library/ruby_gem/jbox2d/lib/custom_listener.rb

@@ -0,0 +1,29 @@
+# A custom listener allows us to get the physics engine to
+# to call our code, on say contact (collisions)
+class CustomListener
+  include ContactListener
+
+  def begin_contact(cp)
+    # Get both fixtures
+    f1 = cp.getFixtureA
+    f2 = cp.getFixtureB
+    # Get both bodies
+    b1 = f1.getBody
+    b2 = f2.getBody
+    # Get our objects that reference these bodies
+    o1 = b1.getUserData
+    o2 = b2.getUserData
+    return unless [o1, o2].all? { |obj| obj.respond_to?(:change) }
+    o1.change
+    o2.change
+  end
+
+  def end_contact(_cp)
+  end
+
+  def pre_solve(_cp, _m)
+  end
+
+  def post_solve(_cp, _ci)
+  end
+end

samples/external_library/ruby_gem/jbox2d/lib/particle.rb

@@ -0,0 +1,77 @@
+# Note the particle class change method is use to change color to red
+# when two particles collide (no change just hitting boundary)
+class Particle
+  extend Forwardable
+  def_delegators(:@app, :box2d, :begin_shape, :end_shape, :line, :pop_matrix,
+                 :ellipse, :translate, :rotate, :stroke, :push_matrix,
+                 :fill, :no_fill, :stroke_weight)
+  attr_accessor :body
+  attr_reader :radius, :col
+
+  def initialize(app, x, y, r)
+    @app, @x, @y, @radius = app, x, y, r
+    # This function puts the particle in the Box2d world
+    make_body(x, y, radius)
+    @col = -5_263_441 # grey
+    body.setUserData(self)
+  end
+
+  # This function removes the particle from the box2d world
+  def kill_body
+    box2d.destroy_body(body)
+  end
+
+  # Change color when hit
+  def change
+    @col = -65_536 # red
+  end
+
+  # Is the particle ready for deletion?
+  def done
+    # Let's find the screen position of the particle
+    pos = box2d.body_coord(body)
+    # Is it off the bottom of the screen?
+    return false unless pos.y > (box2d.height + radius * 2)
+    kill_body
+    true
+  end
+
+  def display
+    # We look at each body and get its screen position
+    pos = box2d.body_coord(body)
+    # Get its angle of rotation
+    a = body.get_angle
+    push_matrix
+    translate(pos.x, pos.y)
+    rotate(a)
+    fill(col)
+    stroke(0)
+    stroke_weight(1)
+    ellipse(0, 0, radius * 2, radius * 2)
+    # Let's add a line so we can see the rotation
+    line(0, 0, radius, 0)
+    pop_matrix
+  end
+
+  # Here's our function that adds the particle to the Box2D world
+  def make_body(x, y, r)
+    # Define a body
+    bd = BodyDef.new
+    # Set its position
+    bd.position = box2d.processing_to_world(x, y)
+    bd.type = BodyType::DYNAMIC
+    @body = box2d.create_body(bd)
+    # Make the body's shape a circle
+    cs = CircleShape.new
+    cs.m_radius = box2d.scale_to_world(r)
+    fd = FixtureDef.new
+    fd.shape = cs
+    # Parameters that affect physics
+    fd.density = 1
+    fd.friction = 0.01
+    fd.restitution = 0.3
+    # Attach fixture to body
+    body.create_fixture(fd)
+    body.set_angular_velocity(rand(-10.0..10))
+  end
+end