;; Example 3-8  Reversing the Geometirc Processing Pipeline

(use gl)
(use gl.glut)
(use srfi-4)

(define (disp)
  (gl-clear GL_COLOR_BUFFER_BIT)
  (gl-flush)
  )

(define (reshape w h)
  (gl-viewport 0 0 w h)
  (gl-matrix-mode GL_PROJECTION)
  (gl-load-identity)
  (glu-perspective 45.0 (/ w h) 1.0 100.0)
  (gl-matrix-mode GL_MODELVIEW)
  (gl-load-identity)
  )

(define (mouse button state x y)
  (cond
   ((= button GLUT_LEFT_BUTTON)
    (if (= state GLUT_DOWN)
        (let* ((viewport (gl-get-integer GL_VIEWPORT))
               (mvmatrix (gl-get-double  GL_MODELVIEW_MATRIX))
               (projmatrix (gl-get-double GL_PROJECTION_MATRIX))
               (real-y   (- (s32vector-ref viewport 3) y 1)))
          (format #t "Coordinates at cursor are (~4d, ~4d)\n" x real-y)
          (receive (wx wy wz)
              (glu-un-project x real-y 0.0 mvmatrix projmatrix viewport)
            (format #t "World coords at z=0.0 are (~s, ~s, ~s)\n"
                    wx wy wz))
          (receive (wx wy wz)
              (glu-un-project x real-y 1.0 mvmatrix projmatrix viewport)
            (format #t "World coords at z=1.0 are (~s, ~s, ~s)\n"
                    wx wy wz))
          )))
   ((= button GLUT_RIGHT_BUTTON)
    (if (= state GLUT_DOWN)
        (exit 0)))
   ))

(define (keyboard key x y)
  (when (= key 27) (exit 0)))

(define (main args)
  (glut-init args)
  (glut-init-display-mode (logior GLUT_SINGLE GLUT_RGB))
  (glut-init-window-size 500 500)
  (glut-init-window-position 100 100)
  (glut-create-window *program-name*)
  (glut-display-func disp)
  (glut-reshape-func reshape)
  (glut-mouse-func mouse)
  (glut-keyboard-func keyboard)
  (glut-main-loop)
  0)