Where the letter shapes come from
FIGlet fonts are plain-text files in the FIGfont format: a header line recording the font's height, baseline, and hardblank character, followed by one glyph block per character, each block exactly as many lines as the font's height. The tool reads the selected font, looks up each character of your input in it, and uses the stored blocks, including the hardblank fill for solid areas, to build the banner.