anchor.diff:               t))))
   
   (defun %get-default-texture-format (attachment)
  -  (assert (keywordp attachment))
  -  (let ((char (char-downcase (aref (symbol-name attachment) 0))))
  -    (cond ((char= char #\c) :rgba8)
  -          ((char= char #\d) :depth-component24)
  -          (t (error "No default texture format for attachment: ~s" attachment)))))
  +  (cond ((numberp attachment) :rgba8)
  +	((eq attachment :d) :depth-component24)
  +	(t (error "No default texture format for attachment: ~s" attachment))))
   
   (defun attachment-compatible (attachment-name image-format)
     (case attachment-name
  
positive.code: ;;----------------------------------------------------------------------
  
  (defun %delete-fbo (fbo)
    (gl:delete-framebuffers (listify (%fbo-id fbo))))
  
  
  (defmethod free ((thing fbo))
  
negative.code: (defvar %valid-texture-subset '(:dimensions :element-type :mipmap :immutable))
  
  (defun %gen-textures (pattern)
    (assert (or (listp pattern) (keywordp pattern)
  	      (numberp pattern)))
    (cond
      ;; simple keyword pattern to texture
      ((or (keywordp pattern)
  	 (numberp pattern))
       (cons (texref
              (make-texture
  	     nil :dimensions (viewport-dimensions (current-viewport))
  