Procedural animated texture generation/Nether portals

To generate one frame of the Nether portal animation:

Due to the large number of Atan2 and Sine operations, all frames of animation (a total of 32, at a resolution of 16x16) for the portal block are generated once at-startup and stored into an internal animation strip. The portal block is the only one of the procedural textures that is ported nearly 1:1 in the 1.5 resource pack changes; For unknown reasons, the transparency of the portal was made uniform rather than based on the blue channel.