win32: fix gl canvas repaint

collects/mred/private/wx/win32/canvas.rkt

@@ -89,6 +89,7 @@
 
      (define hscroll? (memq 'hscroll style))
      (define vscroll? (memq 'vscroll style))
+     (define for-gl? (memq 'gl style))
 
      (define panel-hwnd
        (and (memq 'combo style)
@@ -155,6 +156,8 @@
         [(= msg WM_PAINT)
          (let* ([ps (malloc 128)]
                 [hdc (BeginPaint w ps)])
+           (if for-gl?
+               (queue-paint)
                (unless (positive? paint-suspended)
                  (let* ([hbrush (if no-autoclear?
                                     #f
@@ -167,7 +170,7 @@
                      (unless transparent?
                        (DeleteObject hbrush)))
                    (unless (do-backing-flush this dc hdc)
-                 (queue-paint))))
+                     (queue-paint)))))
            (EndPaint hdc ps))
          0]
         [(= msg WM_NCPAINT)
@@ -254,7 +257,8 @@
      (define/override (refresh) (queue-paint))
 
      (define/public (queue-backing-flush)
-       (InvalidateRect canvas-hwnd #f #f))
+       (unless for-gl?
+         (InvalidateRect canvas-hwnd #f #f)))
 
      (define/public (make-compatible-bitmap w h)
        (send dc make-backing-bitmap w h))