qmk-firmware/docs/quantum_painter_rle.md

QMK QGF/QFF RLE data schema

There are two "modes" to the RLE algorithm used in both QGF/QFF:

• Non-repeating sections of octets, with associated length of up to 128 octets
  • length = marker - 128
  • A corresponding length number of octets follow directly after the marker octet
• Repeated octet with associated length, with associated length of up to 128
  • length = marker
  • A single octet follows the marker that should be repeated length times.

Decoder pseudocode:

while !EOF
    marker = READ_OCTET()

    if marker >= 128
        length = marker - 128
        for i = 0 ... length-1
            c = READ_OCTET()
            WRITE_OCTET(c)

    else
        length = marker
        c = READ_OCTET()
        for i = 0 ... length-1
            WRITE_OCTET(c)