anchor.diff:      `(multiple-value-bind (compiled-stages prog-id prog-ids tfb-group-count)
            (%compile-link-and-upload nil ,primitive ,(serialize-stage-pairs stage-pairs))
          (declare (ignore prog-ids))
  +       (use-program (cepl-context) prog-id)
          (register-lambda-pipeline
           compiled-stages
           (let* (;; all image units will be >0 as 0 is used as scratch tex-unit
                  (image-unit 0)
                  ;; The primitive used by transform feedback. When nil
                  ;; the primitive comes from the render-mode
  -               (tfs-primitive (when tfb-group-count
  +               (tfs-primitive (when (> tfb-group-count 0)
                                   (get-transform-feedback-primitive compiled-stages)))
                  (tfs-array-count tfb-group-count)
                  ;; If there are no implicit-uniforms we need a no-op
  
positive.code:                      (ignorable ,ctx ,@uniform-names))
              #+sbcl(declare (sb-ext:muffle-conditions sb-ext:compiler-note))
              ,@(unless (typep primitive 'varjo::dynamic)
                        `((when stream
                            (assert
                             (= ,(draw-mode-group-id primitive)
                                (buffer-stream-primitive-group-id stream))
                             ()
                             'buffer-stream-has-invalid-primitive-for-stream
                             :name "<lambda>"
                             :pline-prim ',(varjo::lisp-name primitive)
                             :stream-prim (buffer-stream-primitive stream)))))
              (use-program ,ctx prog-id)
              ,@u-uploads
              (funcall implicit-uniform-upload-func prog-id ,@uniform-names)
  
negative.code:                               compiled-stages)))
                 ;;
                 ;; {todo} explain
                 ,@(mapcar λ`(,(assigner-name _) ,(assigner-body _))
                           u-lets))
            (declare (ignorable image-unit)
                     (type function implicit-uniform-upload-func)
                     (type symbol tfs-primitive)
                     (type (unsigned-byte 8) tfs-array-count))
            (use-program (cepl-context) 0)
            ;;
            ;; generate the code that actually renders
            (%post-init ,post)
  