Sun May  9 16:23:47 BST 1999  Adam D. Moss  <adam@gimp.org>

	* app/tile.c
	* app/tile.h
	* app/tile_manager.c
	* app/tile_pvt.h
	* app/paint_funcs.c:

	Added Tile Row Hinting to the GIMP tile structure.  Tiles
	now have cheap per-row hints indicating whether each row is
	all-transparent, all-opaque, a mixture, or other properties.

	These hints are automatically invalidated when the tile is checked
	in as dirty, and are re-evaluated on demand.

	Currently only the layer compositing routines take advantage
	of these hints, though there is opportunity to use them to
	advantage in numerous other places.

	The whole layer compositing process is typically 2x-4x faster
	now, especially on subsequent renders of data which has already
	had its hints calculated.

	See tile.h for the explicit TileRowHint query/set interface.
	The procedure to re-evaluate tile hints currently resides in
	paint_funcs.c but may be exposed to other parts of the core
	if necessary.

	This is experimental.  Please report mis-rendering problems.