OpenGL render a spinning colored cube in Ruby

gistfile1.rb

require 'opengl'
include Gl, Glu, Glut

WIDTH = 512
HEIGHT = 512
NEAR = 0.1
FAR = 1000

class Vec3
  attr_accessor :x, :y, :z
	def initialize x = 0.0, y = 0.0, z = 0.0
		@x, @y, @z = x, y, z
	end
end

class Color
	attr_accessor :r, :g, :b, :a
	def initialize r = 0.0, g = 0.0, b = 0.0, a = 1.0
		@r, @g, @b, @a = r, g, b, a
	end

	def set
		glColor3f(@r, @g, @b, @a)
	end
end

@cam = Vec3.new
@cam.x = 3
@cam.y = 2
@cam.z = 3

@rotation = Vec3.new

def init
	glutInit
	glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH)
	glutInitWindowSize(WIDTH, HEIGHT)
	glutInitWindowPosition(300, 200)
	glutCreateWindow("Ruby 3D!") 
  glEnable(GL_DEPTH_TEST) 
	render_proc = method("render").to_proc
	glutDisplayFunc(render_proc)
  glutIdleFunc(render_proc)
	glutMainLoop()
end

def set_projection
	glMatrixMode(GL_PROJECTION)
	glLoadIdentity()
	gluPerspective(50.0, WIDTH / HEIGHT, NEAR,FAR)
end

def update
	@rotation.y += 0.01
	@rotation.x += 0.005
end

def render
	update()
	glClearColor(0.0, 0.0, 0.0, 1.0)
	glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT)
	glLoadIdentity()
	set_projection
	gluLookAt(@cam.x, @cam.y, @cam.z, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0)
	glRotatef(@rotation.x, 1.0, 0, 0)
	glRotatef(@rotation.y, 0, 1.0, 0)
	glRotatef(@rotation.z, 0, 0, 1.0)
	cube()
	glFlush()
	glutSwapBuffers()
end

def cube
	# White side - BACK
	glBegin(GL_POLYGON);
	glColor3f(   1.0,  1.0, 1.0 )
	glVertex3f(  0.5, -0.5, 0.5 )
	glVertex3f(  0.5,  0.5, 0.5 )
	glVertex3f( -0.5,  0.5, 0.5 )
	glVertex3f( -0.5, -0.5, 0.5 )
	glEnd();
	 
	# Purple side - RIGHT
	glBegin(GL_POLYGON);
	glColor3f(  1.0,  0.0,  1.0 )
	glVertex3f( 0.5, -0.5, -0.5 )
	glVertex3f( 0.5,  0.5, -0.5 )
	glVertex3f( 0.5,  0.5,  0.5 )
	glVertex3f( 0.5, -0.5,  0.5 )
	glEnd();
	 
	# Green side - LEFT
	glBegin(GL_POLYGON)
	glColor3f(   0.0,  1.0,  0.0) 
	glVertex3f( -0.5, -0.5,  0.5) 
	glVertex3f( -0.5,  0.5,  0.5) 
	glVertex3f( -0.5,  0.5, -0.5) 
	glVertex3f( -0.5, -0.5, -0.5) 
	glEnd();
	 
	# Blue side - TOP
	glBegin(GL_POLYGON)
	glColor3f(   0.0,  0.0,  1.0) 
	glVertex3f(  0.5,  0.5,  0.5) 
	glVertex3f(  0.5,  0.5, -0.5) 
	glVertex3f( -0.5,  0.5, -0.5) 
	glVertex3f( -0.5,  0.5,  0.5) 
	glEnd();
	 
	# Red side - BOTTOM
	glBegin(GL_POLYGON)
	glColor3f(   1.0,  0.0,  0.0) 
	glVertex3f(  0.5, -0.5, -0.5) 
	glVertex3f(  0.5, -0.5,  0.5) 
	glVertex3f( -0.5, -0.5,  0.5) 
	glVertex3f( -0.5, -0.5, -0.5) 
	glEnd();
	 
end

init