;; This example illustrates drawing a basic mesh

(import
  scheme
  (chicken base)
  (chicken bitwise)
  (prefix glfw3 #:glfw)
  (prefix epoxy #:gl)
  gl-math
  gl-utils)

(define *vertex* 
#<<END
#version 120
attribute vec2 position;
attribute vec3 color;
varying vec3 c;
uniform mat4 MVP;

void main(){
   gl_Position = MVP * vec4(position, 0.0, 1.0);
   c = color;
}
END
)

(define *fragment*
#<<END
#version 120
varying vec3 c;
void main(){
  gl_FragColor = vec4(c, 1.0);
}
END
)

(define rect (make-mesh
              vertices: '(attributes: ((position #:float 2)
                                       (color #:unsigned-byte 3
                                              normalized: #t))
                          initial-elements: ((position . (-1.0 -1.0
                                                           1.0 -1.0
                                                           1.0  1.0
                                                           -1.0  1.0))
                                             (color . (255 0   0
                                                       0   255 0
                                                       0   0   255
                                                       255 0   255))))
              indices: '(type: #:ushort
                         initial-elements: (0 1 2
                                            0 2 3))))

(define program (make-parameter #f))

(define projection-matrix
  (perspective 640 480 0.1 100 70))

(define view-matrix
  (look-at (make-point 1 0 3)
           (make-point 0 0 0)
           (make-point 0 1 0)))

(define model-matrix (mat4-identity))

(define (render)
  (gl:use-program (program))
  (gl:uniform-matrix4fv (gl:get-uniform-location (program) "MVP")
                        1 #f
                        (m* projection-matrix
                            (m* view-matrix model-matrix)))
  (gl:bind-vertex-array (mesh-vao rect))
  (gl:draw-elements (mode->gl (mesh-mode rect))
                    (mesh-n-indices rect)
                    (type->gl (mesh-index-type rect))
                    #f)

  (check-error)
  (gl:bind-vertex-array 0))

(glfw:key-callback
 (lambda (window key scancode action mods)
   (cond
    ((and (eq? key glfw:+key-escape+) (eq? action glfw:+press+))
     (glfw:set-window-should-close window #t)))))

(glfw:with-window (640 480 "Example" resizable: #f)
  (set! *vertex* (make-shader gl:+vertex-shader+ *vertex*))
  (set! *fragment* (make-shader gl:+fragment-shader+ *fragment*))
  (program (make-program (list *vertex* *fragment*)))
  (mesh-make-vao! rect `((position . ,(gl:get-attrib-location
                                       (program) "position"))
                         (color . ,(gl:get-attrib-location
                                    (program) "color"))))
  (let loop ()
    (glfw:swap-buffers (glfw:window))
    (gl:clear (bitwise-ior gl:+color-buffer-bit+ gl:+depth-buffer-bit+))
    (render)
    (glfw:poll-events)
    (unless (glfw:window-should-close (glfw:window))
      (loop))))