Generate an atlas image an a "description" file for a TrueType font. Very quick and easy, each glyph is packed into the atlas image reasonably well (but probably not perfectly optimally). Then a description file is created. This file contains raw integers in binary format (either signed or unsigned) that indicate where each glyph is in the image, their dimensions, and other parameters to render them correctly.
For more information check the script's argparse help strings or just check the code, it's pretty simple.