source: project/gl-display-glx/gl-proj.scm @ 3547

;;; gl-proj.scm
;;; 2007-03-03 -- thu
;;;
;;; The intent of this file is to provide camera/projection
;;; related procedures : orthographic, FPS camera, ...

(define M_PI 3.14159265358979323846) ; from math.h

(define (orthographic left right bottom top near far)
  (gl:Ortho left right bottom top near far))

;(define *xmin* 0)
;(define *xmax* 0)
;(define *ymin* 0)
;(define *ymax* 0)
(define (perspective fovy aspect znear zfar)
  (let* ((ymax (* znear (tan (/ (* fovy M_PI) 360.0))))
         (ymin (- ymax))
         (xmax (* ymax aspect))
         (xmin (- xmax)))
;    (set! *xmin* xmin)
;    (set! *xmax* xmax)
;    (set! *ymin* ymin)
;    (set! *ymax* ymax)
    (gl:Frustum xmin xmax ymin ymax znear zfar)))

(define (gl-proj:viewport window)
  (let ((w (gl-display:width window))
        (h (gl-display:height window)))
    (gl:Viewport 0 0 w h)))

(define (gl-proj:perspective window)
  (let ((w (gl-display:width window))
        (h (gl-display:height window)))
    (gl:MatrixMode gl:PROJECTION)
    (gl:LoadIdentity)
    (perspective 45 (/ w (if (eq? 0 h) 1 h)) 1 1024)
    (gl:MatrixMode gl:MODELVIEW)
    (gl:LoadIdentity)))

(define (gl-proj:orthographic window)
  (let ((w (gl-display:width window))
        (h (gl-display:height window)))
    (gl:MatrixMode gl:PROJECTION)
    (gl:LoadIdentity)
  ; Q: is it normal that I have to use height-1 and -1, and not height and 0 ?
  ; Maybe 0.375 as in blender ? I think there's a discussion about this in the red book
;    (gl:Ortho 0 w (- h 1) -1 -4 4) ; y goes up
    (gl:Ortho 0 w 0 h -4 4)         ; y goes down
;    (gl:Ortho (- (/ w 2)) (/ w 2) (- (/ h 2)) (/ h 2) -4 4) ; 0/0 at center
;    (gl:Ortho *xmin* *xmax* *ymin* *ymax* -1 1)
    (gl:MatrixMode gl:MODELVIEW)
    (gl:LoadIdentity)))


(define-macro (preserving-matrices . rest)
  `(begin (gl:PushMatrix)
          ,@rest
          (gl:PopMatrix)))