Texture packs are a pretty big thing in Minecraft. They make all your blocks look super lovely. Today’s snapshot - 12w24a - is killing them. For good. They’re never coming back. Thankfully Mojang are merciful gods, and already have a fancy tool ready to transform your texture packs into the newly supported format.
The death of texture packs comes as part of Mojang making the new Resource Pack system live, which is a step forward for the future plugin API. This will replace texture packs, hence the necessary culling of your current textures.
As ever the snapshot includes a bunch of bug fixes alongside the headline act, which this time includes preventing squids taking damage whilst in water (Mojang like to ensure animals can thrive in their natural habitats), ensuring fire animations have all their frames present and correct, and making sure that carpet can be placed everywhere, even on top of iron bars.
You can read the full list at the Mojang website, where you can also grab the tool for converting texture packs and the new launcher to enable snapshot 13w24a.