gir: Add more (out) tags when appropriate

This makes a big difference for bindings, so make sure out-parameters
are properly annotated.

app/core/gimpitem.c

@@ -1134,8 +1134,8 @@ gimp_item_set_size (GimpItem *item,
 /**
  * gimp_item_get_offset:
  * @item:     The #GimpItem to check.
- * @offset_x: Return location for the item's X offset.
- * @offset_y: Return location for the item's Y offset.
+ * @offset_x: (out) (optional): Return location for the item's X offset.
+ * @offset_y: (out) (optional): Return location for the item's Y offset.
  *
  * Reveals the X and Y offsets of the item.
  */
@@ -2584,15 +2584,15 @@ gimp_item_mask_bounds (GimpItem *item,
 /**
  * gimp_item_mask_intersect:
  * @item:   a #GimpItem
- * @x:      return location for x
- * @y:      return location for y
- * @width:  return location for the width
- * @height: return location for the height
+ * @x: (out) (optional): return location for x
+ * @y: (out) (optional): return location for y
+ * @width: (out) (optional): return location for the width
+ * @height: (out) (optional): return location for the height
  *
  * Intersect the area of the @item and its image's selection mask.
  * The computed area is the bounding box of he selection within the
  * item.
- **/
+ */
 gboolean
 gimp_item_mask_intersect (GimpItem *item,
                           gint     *x,

app/core/gimpviewable.c

@@ -725,8 +725,8 @@ gimp_viewable_get_size (GimpViewable  *viewable,
  * @size:        requested size for preview.
  * @popup:       %TRUE if the preview is intended for a popup window.
  * @dot_for_dot: If %TRUE, ignore any differences in X and Y resolution.
- * @width:       return location for the the calculated width.
- * @height:      return location for the calculated height.
+ * @width: (out) (optional):  return location for the the calculated width.
+ * @height: (out) (optional): return location for the calculated height.
  *
  * Retrieve the size of a viewable's preview.  By default, this
  * simply returns the value of the @size argument for both the @width
@@ -765,8 +765,10 @@ gimp_viewable_get_preview_size (GimpViewable *viewable,
  * @width:        the width of the preview from which the popup will be shown.
  * @height:       the height of the preview from which the popup will be shown.
  * @dot_for_dot:  If %TRUE, ignore any differences in X and Y resolution.
- * @popup_width:  return location for the calculated popup width.
- * @popup_height: return location for the calculated popup height.
+ * @popup_width: (out) (optional): return location for the calculated popup
+ *                                  width.
+ * @popup_height: (out) (optional): return location for the calculated popup
+ *                                  height.
  *
  * Calculate the size of a viewable's preview, for use in making a
  * popup. The arguments @width and @height specify the size of the
@@ -1178,7 +1180,8 @@ gimp_viewable_get_dummy_pixbuf (GimpViewable  *viewable,
 /**
  * gimp_viewable_get_description:
  * @viewable: viewable object for which to retrieve a description.
- * @tooltip:  return location for an optional tooltip string.
+ * @tooltip: (out) (optional) (nullable): return location for an optional
+ *                                        tooltip string.
  *
  * Retrieves a string containing a description of the viewable object,
  * By default, it simply returns the name of the object, but this can

libgimpbase/gimprectangle.c

@@ -44,10 +44,14 @@
  * @y2:          origin of second rectangle
  * @width2:      width of second rectangle
  * @height2:     height of second rectangle
- * @dest_x:      return location for origin of intersection (may be %NULL)
- * @dest_y:      return location for origin of intersection (may be %NULL)
- * @dest_width:  return location for width of intersection (may be %NULL)
- * @dest_height: return location for height of intersection (may be %NULL)
+ * @dest_x: (out) (optional): return location for origin of intersection,
+ *                            or %NULL
+ * @dest_y: (out) (optional): return location for origin of intersection,
+ *                            or %NULL
+ * @dest_width: (out) (optional): return location for width of intersection,
+ *                                or %NULL
+ * @dest_height: (out) (optional): return location for height of intersection,
+ *                                 or %NULL
  *
  * Calculates the intersection of two rectangles.
  *
@@ -95,10 +99,10 @@ gimp_rectangle_intersect (gint  x1,
  * @y2:          origin of second rectangle
  * @width2:      width of second rectangle
  * @height2:     height of second rectangle
- * @dest_x:      return location for origin of union (may be %NULL)
- * @dest_y:      return location for origin of union (may be %NULL)
- * @dest_width:  return location for width of union (may be %NULL)
- * @dest_height: return location for height of union (may be %NULL)
+ * @dest_x: (out) (optional): return location for origin of union, or %NULL
+ * @dest_y: (out) (optional): return location for origin of union, or %NULL
+ * @dest_width: (out) (optional): return location for width of union, or %NULL
+ * @dest_height: (out) (optional): return location for height of union, or %NULL
  *
  * Calculates the union of two rectangles.
  *