bitbank2 / oled_animator

C code for converting animated GIF images into a form to run on MCUs and SSD1306 OLED displays

*** OLED Animator ***

OLED SSD1306 animation player using the I2C interface
Copyright (c) 2018 BitBank Software, Inc.
Written by Larry Bank ([e-mail])
Project started 5/21/2018

This player can display compressed animation data on a SSD1306 OLED connected via I2C. The original purpose of the player was to make it easy to run interesting animations on Arduino AVR microcontrollers. Since AVRs don't have much memory (either flash or RAM), the goal of the data compression is to reduce the amount of memory needed for full screen arbitrary animations and reduce the amount of data written to the display so that slower, I2C connections could support good framerates. The compression scheme is my own invention. I'm not claiming that it can't be improved, but it satisfies the goals of being byte-oriented, simple to decompress and doesn't require any RAM on the player side. The data is compressed in 3 ways:

1. Skip - the bytes are identical to those of the previous frame
   
2. Copy - the bytes are different and are copied as-is
   
3. Repeat - a repeating byte sequence
   In order to not keep a copy of the display memory on the player, the skip operations just move the write address (cursor position) on the OLED display. The bytes are packed such that the highest 2 bits of each command byte determine the treatment. They are:
   00SSSCCC - skip+copy (in that order). The 3 bit lengths of each of the skip and copy represent 0-7
   00000000 - special case (long skip). The next byte is the len (1-256)
   01CCCSSS - copy+skip (in that order). Same as above
   01000000 - special case (long copy). The next byte is the len (1-256)
   1RRRRRRR - Repeat the next byte 1-128 times.
   

With those simple operations, typical animated GIF's get compressed between 3 and 6 to 1 (each 1024 byte frame becomes 170 to 341 bytes of compressed data)

*** Note: *** The compressor uses my closed-source imaging library to decode animated GIFs. I need to find a solution to this, so in the mean time, the source code is here (minus the imaging library) and I have included pre-built binaries for Debian Linux and MacOS. I'll resolve this soon as well as provide the Arduino version.