GTK+ 3: treat combo-field% canvas like transparent canvases

The canvas part of a `combo-field%` needs to be non-native
(in the GdkWindow sense), so treat it like a transparent
canvas.

gui-lib/mred/private/wx/gtk/canvas.rkt

@@ -284,6 +284,12 @@
      (define is-combo? (memq 'combo style))
      (define has-border? (or (memq 'border style)
                              (memq 'control-border style)))
+     (define for-gl? (memq 'gl style))
+     (define transparent?
+       (and (memq 'transparent style)
+            (not for-gl?))) ; 'transparent is incompatible with 'gl
+
+     (define transparentish? (or transparent? is-combo?))
 
      (define margin (if has-border? 1 0))
 
@@ -385,17 +391,12 @@
           (let ([client-gtk (as-gtk-allocation (gtk_drawing_area_new))])
             (values client-gtk client-gtk client-gtk #f #f #f #f #f #f 0))])))
 
-     (define for-gl? (memq 'gl style))
      (when for-gl?
        (prepare-widget-gl-context client-gtk gl-config)
        (gtk_widget_set_double_buffered client-gtk #f))
 
      (define dc #f)
 
-     (define transparent?
-       (and (memq 'transparent style)
-            (not (memq 'gl style)))) ; 'transparent is incompatible with 'gl
-
      (super-new [parent parent]
                 [gtk gtk]
                 [client-gtk client-gtk]
@@ -425,7 +426,7 @@
          (reset-auto-scroll))
        (on-size))
      
-     (set! dc (new dc% [canvas this] [transparent? transparent?]))
+     (set! dc (new dc% [canvas this] [transparentish? transparentish?]))
 
      (gtk_widget_realize gtk)
      (gtk_widget_realize client-gtk)
@@ -475,7 +476,7 @@
 
      (when (and gtk3? is-combo?)
        ;; Needed for sizing:
-       (gtk_combo_box_append_text gtk (make-string 10 #\X)))
+       (gtk_combo_box_append_text gtk (make-string 8 #\X)))
 
      (set-auto-size)
      (adjust-client-delta (+ (* 2 margin) 
@@ -550,7 +551,7 @@
      ;; are defined by `canvas-mixin' from ../common/canvas-mixin
      (define/public (queue-paint) (void))
      (define/public (request-canvas-flush-delay)
-       (request-flush-delay (get-flush-window) transparent?))
+       (request-flush-delay (get-flush-window) transparentish?))
      (define/public (cancel-canvas-flush-delay req)
        (cancel-flush-delay req))
      (define/public (queue-canvas-refresh-event thunk)
@@ -593,7 +594,7 @@
        ;; A transparent canvas can't have a native window, so we
        ;; need to release any freezes befre the window implementation
        ;; might change.
-       (when transparent? (unrealize)))
+       (when transparentish? (unrealize)))
 
      (define/public (begin-refresh-sequence)
        (send dc suspend-flush))

gui-lib/mred/private/wx/gtk/dc.rkt

@@ -178,13 +178,13 @@
 (define dc%
   (class backing-dc%
     (init [(cnvs canvas)]
-          transparent?)
+          transparentish?)
     (inherit end-delay)
     (define canvas cnvs)
     (define gl #f)
-    (define is-transparent? transparent?)
+    (define is-transparentish? transparentish?)
 
-    (super-new [transparent? transparent?])
+    (super-new [transparent? transparentish?])
 
     (define/override (get-gl-context)
       (or gl
@@ -194,11 +194,11 @@
 
     (define/override (make-backing-bitmap w h)
       (cond
-       [(and (eq? 'unix (system-type))
+       [(and (not is-transparentish?)
-             (send canvas get-canvas-background))
+             (eq? 'unix (system-type)))
 	(make-object x11-bitmap% w h (send canvas get-client-gtk))]
-       [(and (eq? 'windows (system-type))
+       [(and (not is-transparentish?)
-             (send canvas get-canvas-background))
+             (eq? 'windows (system-type)))
 	(make-object win32-bitmap% w h (widget-window (send canvas get-client-gtk)))]
        [else
 	;; Transparent canvas always use a Cairo bitmap:
@@ -223,7 +223,7 @@
       (send canvas flush))
 
     (define/override (request-delay)
-      (request-flush-delay (send canvas get-flush-window) is-transparent?))
+      (request-flush-delay (send canvas get-flush-window) is-transparentish?))
     (define/override (cancel-delay req)
       (cancel-flush-delay req))))
 

gui-lib/mred/private/wx/gtk/window.rkt

@@ -877,7 +877,7 @@
       (for ([i (in-range (mcdr win-box))])
         (gdk_window_thaw_updates win)))))
 
-(define (request-flush-delay win-box transparent?)
+(define (request-flush-delay win-box transparentish?)
   (do-request-flush-delay 
    win-box
    (lambda (win-box)
@@ -891,7 +891,7 @@
 	    ;; windows; that means we have to be extra careful that
 	    ;; the underlying window doesn't change while a freeze is
 	    ;; in effect; the `reset-child-freezes` helps with that.
-            (unless (and transparent? gtk3?)
+            (unless (and transparentish? gtk3?)
               (gdk_window_ensure_native win))
             (begin
               (gdk_window_freeze_updates win)