libgimp: in GimpTileBackendPlugin, don't read tile data upon TILE_SET

Add an internal _gimp_tile_ref_noinit() function, which increases
the ref-count of a tile *without* initializing its data (in
particular, without reading its data from GIMP, or zeroing it.)
Use this function, instead of gimp_tile_ref(), when storing a tile
in GimpTileBackendPlugin, to avoid unnecessarily reading the tile
data from GIMP.

libgimp/gimptile.c

@@ -86,6 +86,19 @@ gimp_tile_ref (GimpTile *tile)
   gimp_tile_cache_insert (tile);
 }
 
+void
+_gimp_tile_ref_noinit (GimpTile *tile)
+{
+  g_return_if_fail (tile != NULL);
+
+  tile->ref_count++;
+
+  if (tile->ref_count == 1)
+    tile->data = g_new (guchar, tile->ewidth * tile->eheight * tile->bpp);
+
+  gimp_tile_cache_insert (tile);
+}
+
 void
 gimp_tile_unref (GimpTile *tile,
                  gboolean  dirty)

libgimp/gimptile.h

@@ -58,6 +58,8 @@ void    gimp_tile_cache_ntiles (gulong     ntiles);
 
 /*  private function  */
 
+G_GNUC_INTERNAL void _gimp_tile_ref_noinit           (GimpTile     *tile);
+
 G_GNUC_INTERNAL void _gimp_tile_cache_flush_drawable (GimpDrawable *drawable);
 
 

libgimp/gimptilebackendplugin.c

@@ -261,7 +261,7 @@ gimp_tile_write_mul (GimpTileBackendPlugin *backend_plugin,
           gimp_tile = gimp_drawable_get_tile (priv->drawable,
                                               priv->shadow,
                                               y+v, x+u);
-          gimp_tile_ref (gimp_tile);
+          _gimp_tile_ref_noinit (gimp_tile);
 
           {
             gint ewidth           = gimp_tile->ewidth;