anchor.diff:  
   ;;; Image
   (defstruct image
  +  "Simple image structure. Origin is generally top-left but depends on the loader
  +   you use."
     width height bpp data)
   
   (defun create-image (width height bpp)
  
positive.code: (defun end-draw ()
    (update-fps)
    (gl:flush))
  
  ;;; 2D view
  (defstruct 2d-view
  
negative.code:                (+ (* y (cos angle)) (* x (sin angle))))))
    (unless (and (zerop center-x) (zerop center-y))
      (translate-shape shape center-x center-y 0.0)))
  
  (defun scale-shape-2d (shape sx sy)
    (loop for i from 0 below (length (shape-vertices shape)) by 3 do
         (let ((x (aref (shape-vertices shape) i))
               (y (aref (shape-vertices shape) (+ i 1))))
           (setf (aref (shape-vertices shape) i) (* x sx)
                 (aref (shape-vertices shape) (+ i 1)) (* y sy)))))
  
  (defun render-shape (shape &optional (primitive (shape-primitive shape)))
    (gl:begin primitive)
  