Entry 2923

# Purpose: Basic script to build OpenGL applications with Ruby and ruby-opengl
# based upon the example 2 from Nehe's Tutorial

require "gl"
require "glu"
require "glut"

include Gl, Glu, Glut

class GlBase
    ### GlBase.new
    # Main function.
    # Sets the initial parameters of the application and starts it
    #
    def initialize
      @width = 580  # window initial width
      @height = 480 # window initial height
      
      # initialize glut and set projection parameters
      glutInit
      glutInitDisplayMode GLUT_RGB | GLUT_DOUBLE | GLUT_ALPHA | GLUT_DEPTH
      
      # set window atributes and create the window
      glutInitWindowSize @width, @height
      glutInitWindowPosition 0, 0
      @window = glutCreateWindow "An OpenGL program"
      
      # define the glut functions that control the program
      glutDisplayFunc method(:display).to_proc
      glutReshapeFunc method(:reshape).to_proc
      glutKeyboardFunc method(:keyboard).to_proc
      glutIdleFunc method(:idle).to_proc
      
      # init the window
      init_window @width, @height
      # define what is going to be draw
      display
      # start
      glutMainLoop
    end
    
    ###
    # Sets al the necesary parameters for the visualization of the scene
    # var width initial width of the window
    # var height initial height of the window
    def init_window(width, height)
        # set colot, depth and shade parameters
        glClearColor 1.0, 1.0, 1.0, 1.0
        glClearDepth 1.0
        glDepthFunc GL_EQUAL
        glEnable GL_DEPTH_TEST
        glShadeModel GL_SMOOTH
        
        # set projection paramaters
        glMatrixMode GL_PROJECTION
        glLoadIdentity
        
        #calculate and set perspective according to window size
        gluPerspective 45.0, @width / @height, 0.1, 100.0        
    end
    
    ###
    # Modifies projection parameters if the window is resized
    # var width new window width
    # var height new window height
    def reshape(width, height)
        height = 1 if height == 0
        
        glViewport 0, 0, width, height
        
        glMatrixMode GL_PROJECTION
        glLoadIdentity
        
        gluPerspective 45.0, width / height, 0.1, 100.0
    end
    
    ###
    # Watches the keyboard and triggers actions if specific key is pressed
    # var key pressed key
    # var x unused
    # var y unused
    def keyboard(key, x, y)
        case key
        when ?\e
            glutDestroyWindow @window
            exit 0
        end
        glutPostRedisplay
    end
    
    ###
    # Defines what to do if the application is inactive
    def idle
        glutPostRedisplay
    end
    
    ###
    # Defines what is going to be draw in the screen
    def display
        # reset color and depth buffers
        glClear GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT
        
        # sets modelview
        glMatrixMode GL_MODELVIEW
        glLoadIdentity
        
        # translates view
        glTranslatef 0.0, 0.0, -10.0
        
        ### scene code here ###
        
        #######################
        
        # moves buffers so the image is displayed
        glutSwapBuffers
    end
end

GlBase.new