Ensure that the widget is fully onscreen before taking a screenshot.

Otherwise X emits a BadMatch and gtk kills the process (!).
Fix #8220

src/sugar/_sugarext.defs

@@ -200,7 +200,7 @@
   (c-name "sugar_preview_take_screenshot")
   (return-type "none")
   (parameters
-    '("GdkDrawable" "drawable")
+    '("GtkWidget" "widget")
   )
 )
 

src/sugar/_sugarext.override

@@ -22,11 +22,11 @@ headers
 modulename sugar._sugarext
 %%
 import gobject.GObject as PyGObject_Type
+import gtk.Widget as PyGtkWidget_Type
 import gtk.Entry as PyGtkEntry_Type
 import gtk.Menu as PyGtkMenu_Type
 import gtk.Container as PyGtkContainer_Type
 import gtk.gdk.Window as PyGdkWindow_Type
-import gtk.gdk.Drawable as PyGdkDrawable_Type
 import gtk.Image as PyGtkImage_Type
 %%
 ignore-glob

src/sugar/activity/activity.py

@@ -754,8 +754,8 @@ class Activity(Window, gtk.Container):
             return {}
 
     def take_screenshot(self):
-        if self.canvas and self.canvas.window:
-            self._preview.take_screenshot(self.canvas.window)
+        if self.canvas:
+            self._preview.take_screenshot(self.canvas)
 
     def save(self):
         """Request that the activity is saved to the Journal.

src/sugar/sugar-preview.c

@@ -69,16 +69,38 @@ sugar_preview_clear(SugarPreview *preview)
     }
 }
 
+static gboolean
+widget_is_off_screen(GtkWidget *widget)
+{
+    GdkScreen *screen;
+    gint x, y, width, height;
+
+    screen = gtk_widget_get_screen(widget);
+
+    gdk_window_get_geometry(widget->window, &x, &y, &width, &height, NULL);
+
+    return (x < 0 || y < 0 ||
+            x + width > gdk_screen_get_width(screen) ||
+            y + height > gdk_screen_get_height(screen));
+}
+
 void
-sugar_preview_take_screenshot(SugarPreview *preview, GdkDrawable *drawable)
+sugar_preview_take_screenshot(SugarPreview *preview, GtkWidget *widget)
 {
+    GdkDrawable *drawable;
     GdkScreen *screen;
     GdkVisual *visual;
     GdkColormap *colormap;
     gint width, height;
 
+    if (widget->window == NULL || widget_is_off_screen(widget)) {
+        return;
+    }
+    
     sugar_preview_clear(preview);
 
+    drawable = GDK_DRAWABLE(widget->window);
+
     gdk_drawable_get_size(drawable, &width, &height);
 
     screen = gdk_drawable_get_screen(drawable);

src/sugar/sugar-preview.h

@@ -50,7 +50,7 @@ struct _SugarPreviewClass {
 
 GType	   sugar_preview_get_type        (void);
 void       sugar_preview_take_screenshot (SugarPreview *preview,
-                                          GdkDrawable  *drawable);
+                                          GtkWidget    *widget);
 void       sugar_preview_set_size        (SugarPreview *preview,
                                           int width,
                                           int height);