#!/usr/bin/env ruby
# Name:  nehe_lesson02.rb
# Purpose: An implementation of NeHe's OpenGL Lesson #02
#          using ruby-opengl (http://nehe.gamedev.net/)
#

require 'opengl'
require 'glu'
require 'glut'
require 'mathn'

# Add GL and GLUT namespaces in to make porting easier
include Gl
include Glu
include Glut

# Placeholder for the window object
window = nil

def init_gl_window width = 640, height = 480
  # Background color to black
  glClearColor 0.0, 0.0, 0.0, 0
  # Enables clearing of depth buffer
  glClearDepth 1.0
  # Set type of depth test
  glDepthFunc GL_LEQUAL
  # Enable depth testing
  glEnable GL_DEPTH_TEST
  # Enable smooth color shading
  glShadeModel GL_SMOOTH

  glMatrixMode GL_PROJECTION
  glLoadIdentity
  # Calculate aspect ratio of the window
  gluPerspective 45.0, width / height, 0.1, 100.0

  glMatrixMode GL_MODELVIEW

  draw_gl_scene
end

#reshape = Proc.new do |width, height|
def reshape width, height
  height = 1 if height == 0

  # Reset current viewpoint and perspective transformation
  glViewport 0, 0, width, height

  glMatrixMode GL_PROJECTION
  glLoadIdentity

  gluPerspective 45.0, width / height, 0.1, 100.0
end

#draw_gl_scene = Proc.new do
def draw_gl_scene
  # Clear the screen and depth buffer
  glClear GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT

  # Reset the view
  glMatrixMode GL_MODELVIEW
  glLoadIdentity

  # Move left 1.5 units and into the screen 6.0 units
  glTranslatef -1.5, 0.0, -6.0

  # Draw a triangle
  glBegin GL_POLYGON do
    glVertex3f  0.0,  1.0, 0.0
    glVertex3f  1.0, -1.0, 0.0
    glVertex3f -1.0, -1.0, 0.0
  end

  # Move right 3 units
  glTranslatef 3.0, 0.0, 0.0

  # Draw a rectangle
  glBegin GL_QUADS do
    glVertex3f -1.0,  1.0, 0.0
    glVertex3f  1.0,  1.0, 0.0
    glVertex3f  1.0, -1.0, 0.0
    glVertex3f -1.0, -1.0, 0.0
  end

  # Swap buffers for display
  glutSwapBuffers
end

# The idle function to handle
def idle
  glutPostRedisplay
end

# Keyboard handler to exit when ESC is typed
keyboard = lambda do |key, x, y|
  case key
  when ?\e
    glutDestroyWindow window
    exit(0)
  end
  glutPostRedisplay
end


# Initliaze our GLUT code
glutInit
# Setup a double buffer, RGBA color, alpha components and depth buffer
glutInitDisplayMode GLUT_RGB | GLUT_DOUBLE | GLUT_ALPHA | GLUT_DEPTH
glutInitWindowSize 640, 480
glutInitWindowPosition 0, 0
window = glutCreateWindow "NeHe Lesson 02 - ruby-opengl version"
glutIdleFunc :idle
glutDisplayFunc :draw_gl_scene
glutReshapeFunc :reshape
glutKeyboardFunc keyboard
init_gl_window 640, 480
glutMainLoop
