[gtk+] gtk_image_get_surface: Add docs

[Alexander Larsson <alexl src gnome org>]

commit d22c91127f185c5572f05043570aba158dc43af5
Author: Alexander Larsson <alexl redhat com>
Date:   Sun Oct 22 22:57:55 2017 +0200

    gtk_image_get_surface: Add docs

 gtk/gtkimage.c |   14 ++++++++++++++
 1 files changed, 14 insertions(+), 0 deletions(-)
---
diff --git a/gtk/gtkimage.c b/gtk/gtkimage.c
index ac9f347..d0e65f7 100644
--- a/gtk/gtkimage.c
+++ b/gtk/gtkimage.c
@@ -1087,6 +1087,20 @@ gtk_image_get_pixbuf (GtkImage *image)
   return _gtk_icon_helper_peek_pixbuf (&priv->icon_helper);
 }
 
+/**
+ * gtk_image_get_surface:
+ * @image: a #GtkImage
+ *
+ * Gets the image #cairo_surface_t being displayed by the #GtkImage.
+ * The storage type of the image must be %GTK_IMAGE_EMPTY or
+ * %GTK_IMAGE_SURFACE (see gtk_image_get_storage_type()).
+ * The caller of this function does not own a reference to the
+ * returned surface.
+ * 
+ * Returns: (nullable) (transfer none): the displayed surface, or %NULL if
+ *   the image is empty
+ * Since: 3.94.0
+ **/
 cairo_surface_t *
 gtk_image_get_surface (GtkImage *image)
 {