Custom reaction packs are a series of three transparent .png or .gif spritemaps: 32px by 256px, 48px by 384px, and 96px by 768px. Each one contains sprites for reactions in this order:
- confused (not used)
- yay (not used)
For example, here's the 32px by 256 spritemap for the Soot Sprites pack:
Even though confused and yay aren't used, include them (or blank space where they should be) so we don't throw off where Facebook's sprite position calculations. I recommend making your reactions circular to maintain consistency with the OG reactions.
If you have any questions about the process, contact Rodney Folz at @rodneyfolz on Twitter.