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.
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.