require 'opengl'
include Gl,Glu,Glut

MAXZ=1.0
MINZ=-2.0
ZINC=0.1

$solidZ = MAXZ
$transparentZ = MINZ
$sphereList=nil
$cubeList=nil

def init
	mat_specular = [ 1.0, 1.0, 1.0, 0.15 ]
	mat_shininess = [ 100.0 ]
	position = [ 0.5, 0.5, 1.0, 0.0 ]

	glMaterial(GL_FRONT, GL_SPECULAR, mat_specular)
	glMaterial(GL_FRONT, GL_SHININESS, mat_shininess)
	glLight(GL_LIGHT0, GL_POSITION, position)

	glEnable(GL_LIGHTING)
	glEnable(GL_LIGHT0)
	glEnable(GL_DEPTH_TEST)

	$sphereList = glGenLists(1)
	glNewList($sphereList, GL_COMPILE)
	glutSolidSphere(0.4, 16, 16)
	glEndList()

	$cubeList = glGenLists(1)
	glNewList($cubeList, GL_COMPILE)
	glutSolidCube(0.6)
	glEndList()
end

display = proc do
	mat_solid = [ 0.75, 0.75, 0.0, 1.0 ]
	mat_zero = [ 0.0, 0.0, 0.0, 1.0 ]
	mat_transparent = [ 0.0, 0.8, 0.8, 0.6 ]
	mat_emission = [ 0.0, 0.3, 0.3, 0.6 ]

	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)

	glPushMatrix()
	glTranslate(-0.15, -0.15, $solidZ)
	glMaterial(GL_FRONT, GL_EMISSION, mat_zero)
	glMaterial(GL_FRONT, GL_DIFFUSE, mat_solid)
	glCallList($sphereList)
	glPopMatrix()

	glPushMatrix()
	glTranslate(0.15, 0.15, $transparentZ)
	glRotate(15.0, 1.0, 1.0, 0.0)
	glRotate(30.0, 0.0, 1.0, 0.0)
	glMaterial(GL_FRONT, GL_EMISSION, mat_emission)
	glMaterial(GL_FRONT, GL_DIFFUSE, mat_transparent)
	glEnable(GL_BLEND)
	glDepthMask(GL_FALSE)
	glBlendFunc(GL_SRC_ALPHA, GL_ONE)
	glCallList($cubeList)
	glDepthMask(GL_TRUE)
	glDisable(GL_BLEND)
	glPopMatrix()

	glutSwapBuffers()
end

reshape = proc do |w, h|
	glViewport(0, 0,  w,  h)
	glMatrixMode(GL_PROJECTION)
	glLoadIdentity()
	if (w <= h)
		glOrtho(-1.5, 1.5, -1.5*h.to_f/w, 1.5*h.to_f/w, -10.0, 10.0)
	else
		glOrtho(-1.5*w.to_f/h, 1.5*w.to_f/h, -1.5, 1.5, -10.0, 10.0)
	end
	glMatrixMode(GL_MODELVIEW)
	glLoadIdentity()
end

animate = proc do
	if ($solidZ <= MINZ || $transparentZ >= MAXZ)
		glutIdleFunc(nil)
	else
		$solidZ -= ZINC
		$transparentZ += ZINC
		glutPostRedisplay()
	end
end

keyboard = proc do |key, x, y|
	case (key)
		when ?a,?A
			$solidZ = MAXZ
			$transparentZ = MINZ
			glutIdleFunc(animate)
		when ?r, ?R
			$solidZ = MAXZ
			$transparentZ = MINZ
			glutPostRedisplay()
		when 27
			exit(0)
	end
end

glutInit()
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH)
glutInitWindowSize(500, 500)
glutInitWindowPosition(100, 100)
glutCreateWindow($0)
init()
glutReshapeFunc(reshape)
glutKeyboardFunc(keyboard)
glutDisplayFunc(display)
glutMainLoop()