End Portal Frame

An end portal frame is a block which resembles end stone with a decorative bluish-green top, with sides decorated in hollow rounded rectangles with the same color as the top.

Natural generation
The end portal generates naturally in stronghold portal rooms over a pool of lava with a staircase containing a silverfish spawner. It generates end portal blocks in a 5×5 square border, without the corners. Each end portal block generates facing inwards, with a 10% chance of containing an eye of ender.

Each Stronghold only contains one end portal, On the Java and Bedrock Editions, each world contains 128 strongholds, so a total of 1,536 end portal blocks are generated. In the Legacy Console Edition, there is only one portal per world, so only 12 are generated.

There is an extremely low chance (10-12 or 10-10% or One in a Trillion) for all twelve end portal frames to be filled in strongholds.

Obtaining
The end portal blocks, like bedrock, are indestructible in Survival or Adventure mode. It can only be obtained by accessing the creative inventory or commands.

Usage
eyes of Ender on end portal blocks inserts them to the top of the blocks if it is not inserted previously.

End portal frames have a front facing which faces the player when placed. Although the facing is almost invisible (one can only distinguish 2 rotations of end portal frames), all end portal frame blocks must be placed correctly and face inward in order to be able to activate the end portal, and if all of the frame blocks have eyes of Ender inserted, the portal will activate, replacing the inner 3×3 space with end portal blocks.

In the end the end portal blocks will teleport entities back to the overworld, so entering an activated end portal in the end will make the entity travel to the overworld instead.

Redstone
End portal blocks will output a redstone comparator signal of 15 when an eye is present. If there is no eye in the frame, it outputs a signal of 0.

Light source
End portals emit a light level of 1.

Block data
The bottom two bits determine which "side" of the whole portal frame this block is a part of. To make the frame activate, each of the portal frame blocks in the pattern must "face" toward the middle. Since the image is near-symmetrical, it is difficult to tell which direction an individual block is actually facing, but if the block isn't facing in that direction and that is the last frame block where the Eye of Ender is placed, the frame won't activate.

Direction vectors for the blocks are the following:


 * 0: To the
 * 1: To the
 * 2: To the
 * 3: To the

0x4 is a bit flag: 0 is an "empty" frame block, 1 is a block with an eye of ender inserted.

Trivia

 * When an end portal block is broken after being activated, the portal itself will not be deactivated.
 * When an end portal block is placed, it will act like bedrock and it cannot be broken in gamemodes besides Creative mode.
 * When broken, these blocks make the same breaking noise as glass blocks.
 * An interesting feature of the end portal frame (and the spawner, barrier, and slime block) is that they are transparent in their rendering only - unlike most other transparent blocks, they can have torches and redstone placed on them, will suffocate mobs, and more.