gistfile1.lisp

;;; Blend a masked source image with a target

(defun cocoa-blend (target source mask offset size)
  (declare #.*optimize*
           (type fixnum size offset)
           (inline fli:dereference (setf fli:dereference)))
  (loop for i fixnum from offset below (the fixnum (+ offset size)) 
     for j fixnum from 0 below size do

       (let ((dst (fli:dereference target :index i :type '(:unsigned :char)))
             (src (fli:dereference source :index j :type '(:unsigned :char)))
             (alpha (fli:dereference mask :index j :type '(:unsigned :char))))
         (declare (type fixnum dst src alpha))

         (when (> alpha 0)
           (setf (fli:dereference target :index i :type '(:unsigned :char))
                 (the fixnum 
                   (truncate (/ (+ (* src alpha) (* dst (- 255 alpha))) 255))))
         
         ))))