Blip

Blip is the name of a mechanic that allow the player to land at unintended heights, which can be abused to jump higher.

It's the consequence of Stepping applied to falling motion.

There are three types of blips in 1.8:


 * The "Normal Blip", which involves landing next to wall to walk on top of it (intended).
 * The Blip-Up, which involves landing next to a low wall to trick the game into landing the player mid-air.
 * The Wall Blip, which involves landing next to an X-facing wall with a ceiling above it. (Same effect as blip-ups)

[video]

Blip-Up
When the player lands, the game checks for wall collisions, and attempts to make the player step onto surrounding obstacles. It does that the same as it would for regular stepping:


 * Reset the player's bounding box
 * Elevate the bounding box (by 0.6b at most)
 * Move the bounding box horizontally (X then Z)
 * Lower the bounding box down (by 0.6b at most)

This procedure is intended to make the player hop over any low obstacle. The fatal flaw is that the bounding box is reset to the player's position at the start of the tick, and then applies stepping. If the player was airborne at the start of the tick, the stepping maneuver is initiated above where it's supposed to. In that case, the bounding box isn't lowered enough and stops mid-air.

With this glitch called Blip-Up, the player is able to "land" above ground and retain the ability to jump. With these two advantages, the player is able to jump higher than intended.

The requirements for doing a blip-up are as follow:


 * Have negative vertical speed (by falling or jumping)
 * Land next to a wall of relatively low height (e.g carpet, lilypad) - it should be lower than the player's height on the landing tick.

When building a setup for blip-up, the rule of thumb is have both surfaces at the same tier relative to the starting height.


 * The effect of a blip-up generally increases the faster the player falls.
 * The setup should be carefully adjusted to leave as much space as possible between the player and the ground on the landing tick.
 * The height gain could be anywhere between 0b and 3.92b (terminal velocity). The taller the wall, the less effective the setup becomes.

Examples of a simple and effective setups:

Wall Blip
Wall Blips were discovered much later than Blip-Ups, due to the precise setup and conditions they require.

This blip variant happen due to the same quirks of the code concerning collisions, but are trickier to understand and perform.

https://youtu.be/vueSpP-P53U

In short, a Wall Blip is performed by landing near the corner of an X-facing wall, with a ceiling above the inner portion.

However, that is a very simplistic description that doesn't explain how and why the glitch works.

The ceiling can be up to 0.6m above the player's head before landing, but it's easier if the ceiling is below head level.

Chained Blips


Blip-Ups and Wall Blips can be performed repeatedly on the same setup to gain more and more height.

This cannot be repeated forever, as the player is eventually too far above the ground, so they must fall for one extra tick and repeat the process.

Chained Blip-Ups
Each consecutive blip-up adds an extra 0.104 height, with occasional height losses every 1-4 jumps.


 * You can only blip once on 3 snow layers (4px) -> +0.104
 * You can chain up to 2 blips on a trapdoor (3px) -> +0.208
 * You can chain up to 3 blips on a carpet* (1px) -> +0.312
 * You can chain up to 4 blips on a lilypad (0.25 px) -> +0.416

You can chain 4 blip-ups on a carpet if you start from the lower part of the blip, but at the cost of some initial height (+0.353 total).

Technically, you can chain blip-ups for longer, losing some height once in a while to fall back in blipping range... until you eventually reach a height below the top surface, at which point the whole cycle restarts.

pa_O1dmuLe8

Chained Wall Blips
Wall Blips can be chained in the same way as Blip-ups, with the same cycle and height gains at first.

Unlike chained blip-ups, wall blips can be chained indefinitely. The resulting sequence of jump heights is pseudo-random, never reaching a maximum value.

In that sense, it's possible to create artificially difficult jumps.

Pre-1.8 :
Up until version 1.7.10, a bug prevented entities from walking onto a step under a ceiling.

Blips worked in before 1.8, but the Wall Blip variant was less lenient with the ceiling height (0.6m less than in 1.8)

1.9+ :
Because you jump higher in 1.9+ (1.252 compared to 1.249), blips are slightly affected but the mechanic still behaves the same.

For chained blips in 1.9+, each consecutive blip adds 0.121 to your initial Y position (instead of 0.104)


 * You can only blip once on 3 snow layers (4px) -> +0.121
 * You can chain up to 2 blips on a repeater (2px) -> +0.242
 * You can chain up to 3 blips on a carpet (1px) -> +0.363
 * You can no longer chain 4 blips on a lilypad or carpet.

1.14+ :
This version supposedly patched the blip glitch by extending the stepping region lower: the default step height is now "1 tick later" than in pre-1.14, which introduces a new glitch called Blip-Down, where the player can land below ground level under the right conditions.

To perform a blip-down, the player must land on the edge of a block, collide with a steppable wall, while moving outwards to ensure the stepping region doesn't encounter any ground.

This glitch is not as useful as the blip-up, but it allows for new and interesting jumps to be possible. It can also be chained to gain more momentum by reducing the duration of each jump, though it would require a peculiar setup.

Wall Blips have been completely patched.

1.15+ :
Blipping now cancels fall damage in some cases.