Bugzilla

          // We only want to remove the area of the child widget from the area

          // we have to update if the child widget is opaque.

          if (childWidget->GetTransparencyMode() == eTransparencyOpaque) {

            // GetBounds should compensate for chrome on a toplevel widget

            nsIntRect bounds;

            childWidget->GetBounds(bounds);

            nsIntPoint offset = bounds.TopLeft();

            // popup widget's bounds are in screen coords, not relative to

            // their parent widget, so we need an extra offset to translate

            // to the parent widget in that case.

            nsWindowType type;

            childWidget->GetWindowType(type);

            if (type == eWindowType_popup) {

              offset -= aWidget->WidgetToScreenOffset();

            }

            nsTArray<nsIntRect> clipRects;

            childWidget->GetWindowClipRegion(&clipRects);

            for (PRUint32 i = 0; i < clipRects.Length(); ++i) {

              nsRect rr = (clipRects[i] + offset).

                ToAppUnits(AppUnitsPerDevPixel());

              children.Or(children, rr - aWidgetView->ViewToWidgetOffset()); 

              children.SimplifyInward(20);

            }