#
# Copyright (c) 1993-1997, Silicon Graphics, Inc.
# ALL RIGHTS RESERVED
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# any purpose and without fee is hereby granted, provided that the above
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# LOSS OF PROFIT, LOSS OF USE, SAVINGS OR REVENUE, OR THE CLAIMS OF
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# ADVISED OF THE POSSIBILITY OF SUCH LOSS, HOWEVER CAUSED AND ON
# ANY THEORY OF LIABILITY, ARISING OUT OF OR IN CONNECTION WITH THE
# POSSESSION, USE OR PERFORMANCE OF THIS SOFTWARE.
#
# US Government Users Restricted Rights
# Use, duplication, or disclosure by the Government is subject to
# restrictions set forth in FAR 52.227.19(c)(2) or subparagraph
# (c)(1)(ii) of the Rights in Technical Data and Computer Software
# clause at DFARS 252.227-7013 and/or in similar or successor
# clauses in the FAR or the DOD or NASA FAR Supplement.
# Unpublished-- rights reserved under the copyright laws of the
# United States.  Contractor/manufacturer is Silicon Graphics,
# Inc., 2011 N.  Shoreline Blvd., Mountain View, CA 94039-7311.
#
# OpenGL(R) is a registered trademark of Silicon Graphics, Inc.
#
#
# select.c
# This is an illustration of the selection mode and
# name stack, which detects whether objects which collide
# with a viewing volume.  First, four triangles and a
# rectangular box representing a viewing volume are drawn
# (drawScene routine).  The green triangle and yellow
# triangles appear to lie within the viewing volume, but
# the red triangle appears to lie outside it.  Then the
# selection mode is entered (selectObjects routine).
# Drawing to the screen ceases.  To see if any collisions
# occur, the four triangles are called.  In this example,
# the green triangle causes one hit with the name 1, and
# the yellow triangles cause one hit with the name 3.
require 'opengl'
require 'glu'
require 'glut'
include Gl,Glu,Glut

# draw a triangle with vertices at (x1, y1), (x2, y2)
# and (x3, y3) at z units away from the origin.
def drawTriangle(x1, y1, x2, y2, x3, y3, z)
  glBegin(GL_TRIANGLES)
  glVertex(x1, y1, z)
  glVertex(x2, y2, z)
  glVertex(x3, y3, z)
  glEnd()
end

# draw a rectangular box with these outer x, y, and z values
def drawViewVolume(x1, x2, y1, y2, z1, z2)
  glColor(1.0, 1.0, 1.0)
  glBegin(GL_LINE_LOOP)
  glVertex(x1, y1, -z1)
  glVertex(x2, y1, -z1)
  glVertex(x2, y2, -z1)
  glVertex(x1, y2, -z1)
  glEnd()

  glBegin(GL_LINE_LOOP)
  glVertex(x1, y1, -z2)
  glVertex(x2, y1, -z2)
  glVertex(x2, y2, -z2)
  glVertex(x1, y2, -z2)
  glEnd()

  glBegin(GL_LINES)# 4 lines
  glVertex(x1, y1, -z1)
  glVertex(x1, y1, -z2)
  glVertex(x1, y2, -z1)
  glVertex(x1, y2, -z2)
  glVertex(x2, y1, -z1)
  glVertex(x2, y1, -z2)
  glVertex(x2, y2, -z1)
  glVertex(x2, y2, -z2)
  glEnd()
end

# drawScene draws 4 triangles and a wire frame
# which represents the viewing volume.
def drawScene()
  glMatrixMode(GL_PROJECTION)
  glLoadIdentity()
  gluPerspective(40.0, 4.0/3.0, 1.0, 100.0)

  glMatrixMode(GL_MODELVIEW)
  glLoadIdentity()
  gluLookAt(7.5, 7.5, 12.5, 2.5, 2.5, -5.0, 0.0, 1.0, 0.0)
  glColor(0.0, 1.0, 0.0)# green triangle
  drawTriangle(2.0, 2.0, 3.0, 2.0, 2.5, 3.0, -5.0)
  glColor(1.0, 0.0, 0.0)# red triangle
  drawTriangle(2.0, 7.0, 3.0, 7.0, 2.5, 8.0, -5.0)
  glColor(1.0, 1.0, 0.0)# yellow triangles
  drawTriangle(2.0, 2.0, 3.0, 2.0, 2.5, 3.0, 0.0)
  drawTriangle(2.0, 2.0, 3.0, 2.0, 2.5, 3.0, -10.0)
  drawViewVolume(0.0, 5.0, 0.0, 5.0, 0.0, 10.0)
end

# processHits prints out the contents of the selection array
def processHits(hits, buffer)
  printf("hits = %d\n", hits)
  ptr = buffer.unpack("I*")
  p = 0
  for i in 0...hits   # for each hit
    names = ptr[p]
    printf(" number of names for hit = %d\n", names); p+=1
    printf("  z1 is %g",  ptr[p].to_f/0xffffffff); p+=1
    printf(" z2 is %g\n",  ptr[p].to_f/0xffffffff); p+=1
    printf("   the name is ")
    for j in 0...names  # for each name
      printf("%d ", ptr[p]); p+=1
    end
    printf("\n")
  end
end

# selectObjects "draws" the triangles in selection mode,
# assigning names for the triangles.  Note that the third
# and fourth triangles share one name, so that if either
# or both triangles intersects the viewing/clipping volume,
# only one hit will be registered.

BUFSIZE=512

def selectObjects
  selectBuf = glSelectBuffer(BUFSIZE)
  glRenderMode(GL_SELECT)

  glInitNames()
  glPushName(0)

  glPushMatrix()
  glMatrixMode(GL_PROJECTION)
  glLoadIdentity()
  glOrtho(0.0, 5.0, 0.0, 5.0, 0.0, 10.0)
  glMatrixMode(GL_MODELVIEW)
  glLoadIdentity()
  glLoadName(1)
  drawTriangle(2.0, 2.0, 3.0, 2.0, 2.5, 3.0, -5.0)
  glLoadName(2)
  drawTriangle(2.0, 7.0, 3.0, 7.0, 2.5, 8.0, -5.0)
  glLoadName(3)
  drawTriangle(2.0, 2.0, 3.0, 2.0, 2.5, 3.0, 0.0)
  drawTriangle(2.0, 2.0, 3.0, 2.0, 2.5, 3.0, -10.0)
  glPopMatrix()
  glFlush()

  hits = glRenderMode(GL_RENDER)
  processHits(hits, selectBuf)
end

def init
  glEnable(GL_DEPTH_TEST)
  glShadeModel(GL_FLAT)
end

display = proc do
  glClearColor(0.0, 0.0, 0.0, 0.0)
  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
  drawScene()
  selectObjects()
  glFlush()
end

keyboard = proc do |key, x, y|
  case (key)
    when ?\e
      exit(0)
  end
end

# Main Loop

GLUT.Init
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH)
glutInitWindowSize(500, 500)
glutInitWindowPosition(100, 100)
glutCreateWindow $0
init()
glutDisplayFunc(display)
glutKeyboardFunc(keyboard)
glutMainLoop()
