fill_view_matrix   xtlang

;; this is similar to gl_look_at
;; but returns a suitable VIEW matrix
(bind-func fill_view_matrix
  (let ((orientation_matrix:float* (alloc 16))
        (translation_matrix:float* (alloc 16))
        (vz:float* (alloc 3)) ;; vector z axes
        (vy:float* (alloc 3)) ;; vector y axes
        (vx:float* (alloc 3)) ;; vector x axes
        (vtmp:float* (alloc 3)))
    (lambda (matrix:float* vEye vTarget vUp)
      (let ((i 0))
        (vvsub vEye vTarget 3 vtmp)
        (vnormalise vtmp 3 vz) ;; gives z axes
        ;; cross z with up
        (vvcross vUp vz vtmp)
        (vnormalise vtmp 3 vx) ;; gives x axes
        (vvcross vz vx vy) ;; gives y axes
        ;; (pfill! mat
        ;;         (pref vx 0) (pref vx 1) (pref vx 2) 0.0
        ;;         (pref vy 0) (pref vy 1) (pref vy 2) 0.0
        ;;         (pref vz 0) (pref vz 1) (pref vz 2) 0.0
        ;;         (pref vEye 0) (pref vEye 1) (pref vEye 2) 1.0)
        (pfill! orientation_matrix
                (pref vx 0) (pref vy 0) (pref vz 0) 0.0
                (pref vx 1) (pref vy 1) (pref vz 1) 0.0
                (pref vx 2) (pref vy 2) (pref vz 2) 0.0
                0.0 0.0 0.0 1.0)
        (pfill! translation_matrix
                1.0 0.0 0.0 0.0
                0.0 1.0 0.0 0.0
                0.0 0.0 1.0 0.0
                (* -1.0 (pref vEye 0)) (* -1.0 (pref vEye 1)) (* -1.0 (pref vEye 2)) 1.0)
        ;; (minverse mat 4 matrix)
        (mmmul translation_matrix orientation_matrix matrix)
        void))))