Blip/zh

Blipping is a mechanic that allows 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 a 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)

Blip-Up
https://youtu.be/BjNbUP5-4wo

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 low obstacles. 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 might not get lowered enough and stops mid-air. In this scenario, the glitch is called a Blip-Up

With this glitch, the player is able to "land" above ground and retain the ability to jump, therefore being able to jump higher than intended.

Requirements:

 * 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.

Setups:
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 setups:
 * +1.5b setup
 * +1.75b setup

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

The role of the wall is to trigger the stepping mechanic (even though the wall itself cannot be stepped onto) The role of the ceiling is to redirect the player in a different route, in an attempt to exploit the "best of 2 routes" procedure.

Requirements:

 * The ceiling must be at least 1.8b above the ground, and at most 0.6b above the player's head on the landing tick.
 * The wall must be X-facing (in order to direct the initial route inside the hole)
 * The player must have position and velocity such that the redirected route goes further horizontally than the initial route.

This last requirement is a bit confusing, so let's illustrate it with a diagram and formula:



On the landing tick, if $(v_X,v_Z)$ is the player's velocity, and $(\delta_X,\delta_Z)$  is the offset between the player and the corner of the wall, the requirement is:

$$\sqrt{\delta_X^2 + v_Z^2} > \sqrt{v_X^2 + \delta_Z^2}$$

Chained Blips


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

This trick cannot be stacked to reach unlimited heights: eventually, the player is high enough that the jump takes one more tick to land, thereby losing most of the height gained.

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).

The player will eventually reach a height lower than the top surface, thereby losing all their progress. In that sense, chained blip-ups are cyclic.

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Chained Wall Blips
Wall Blips can be chained in the same way as Blip-ups.

Unlike chained blip-ups, wall blips can be chained indefinitely, and 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 before 1.8, but could behave a bit differently in some setups due to this bug.


 * 1.8.0 is slightly different from 1.8.1+ (always lowers the bounding box by 0.6b, even when a ceiling was encountered) This difference generally has no effect on blips, but it does affect Jump-Cancelling (makes grinding impossible in 1.8.0)

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 -> +0.121
 * You can chain up to 2 blips on a repeater -> +0.242
 * You can chain up to 3 blips on a carpet -> +0.363
 * You can no longer chain 4 blips on a lilypad or carpet.

1.14+ :
Blip-ups and Wall blips are patched. "Normal" blips still works, suggesting it's an intended mechanic.


 * Instead of lowering the bounding box by a maximum of 0.6m, the game now lowers it until it reaches the player's height minus their vertical speed.


 * This 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.

1.15+ :
Blipping now cancels fall damage in some cases. (patched in 1.16)