imagesettile() sets the tile image to be
used by all region filling functions (such as imagefill()
and imagefilledpolygon()) when filling with the special
A tile is an image used to fill an area with a repeated pattern. Any
GD image can be used as a tile, and by setting the transparent color index of the tile
image with imagecolortransparent(), a tile allows certain parts
of the underlying area to shine through can be created.
You need not take special action when you are finished with a tile, but if you
destroy the tile image, you must not use the IMG_COLOR_TILED
color until you have set a new tile image!