Simple test showing big-bang being slow at rendering on screen in new version

big-bang-slowness.rkt

#lang racket

;;; Run this file with `racket test-big-bang.rkt`
;;; then type quickly "asdf" to trigger several successive to-draw events.
;;; Drawing the scene is fast, but rendering it on-screen is very slow?

(require 2htdp/image
         2htdp/planetcute
         2htdp/universe)

(define elt-width (image-width grass-block))
(define elt-height (image-height grass-block))
(define elt-height/2 (/ elt-height 2))

(define view-width 800)
(define view-height 400)
(define window-width view-width)
(define window-height (+ view-height elt-height))

(define grid-size 10)

(define (stack-rows . col-picts)
  (for/fold ([img empty-image])
    ([cp col-picts])
    (underlay/align/offset 
                    "center" "bottom"
                    img 0 elt-height/2 cp)))

(define (client-draw-all)
  (apply stack-rows
         (for/list ([i grid-size])
           (apply beside/align "bottom" 
                  (for/list ([j grid-size])
                        grass-block)))))

(define t0 (current-milliseconds))
(define (print-time str)
  (printf "~a at ~a\n" str (- (current-milliseconds) t0)))

(big-bang 
 '()
 (to-draw (λ(w)
            (print-time "to-draw")
            (display "to-draw: ")
            (time 
             #;(empty-scene window-width window-height)
             (client-draw-all)))
          window-width window-height)
 (on-key (λ(w k)(print-time (format "on-key ~a" k)))))

Timings:

to-draw at 2
to-draw: cpu time: 0 real time: 2 gc time: 0
on-key a at 6906
on-key u at 6912
on-key i at 6912
on-key e at 6913
to-draw at 6913
to-draw: cpu time: 4 real time: 3 gc time: 0
to-draw at 8598
to-draw: cpu time: 4 real time: 2 gc time: 0
to-draw at 11948
to-draw: cpu time: 4 real time: 2 gc time: 0
to-draw at 13631
to-draw: cpu time: 0 real time: 2 gc time: 0
to-draw at 161839
to-draw: cpu time: 4 real time: 9 gc time: 0