# 🏃 Move

**`#bs.move:help`**

Make your entity move exactly the way you want it to!

```{image} /_imgs/modules/move.png
:align: center
:class: dark_light
```

```{epigraph}
"There is nothing permanent except change."

-- Heraclitus
```

```{button-link} https://youtu.be/V6NxxpN_hhc
:color: primary
:align: center
:shadow:

{octicon}`device-camera-video` Watch a demo
```

---

## 🔧 Functions

You can find below all functions available in this module.

---

### Apply Velocity

:::::{tab-set}
::::{tab-item} Canonical

```{function} #bs.move:apply_vel {scale:<scaling>,with:{}}

Teleport an entity by its velocity scores while handling collisions.

:Inputs:
  **Execution `as <entities>`**: Entity to move.

  **Scores `@s bs.vel.[x,y,z]`**: Canonical velocity vector.

  **Function macro**:
  :::{treeview}
  - {nbt}`compound` Arguments
    - {nbt}`number` **scale**: Scalar applied to the output.
    - {nbt}`compound` **with**: Collision settings.
      - {nbt}`bool` **blocks**: Whether the entity should collide with blocks (default: true).
      - {nbt}`bool` {nbt}`string` **entities**: Whether the entity should collide with entities (default: false). Can also be a tag that entities must have.
      - {nbt}`string` **hitbox_shape**: Hitbox type: `interaction` or `collision` (default: `collision`).
      - {nbt}`string` **ignored_blocks**: Blocks to ignore (default: `#bs.hitbox:can_pass_through`).
      - {nbt}`string` **ignored_entities**: Entities to ignore (default: `#bs.hitbox:intangible`).
      - {nbt}`string` **on_collision**: Command to run when a collision occurs, used to resolve the collision (default: `function #bs.move:callback/bounce`).
  :::

:Outputs:
  **State**: Entity is teleported according to its velocity scores.
```

::::
::::{tab-item} Local

`````{function} #bs.move:apply_local_vel {scale:<scaling>,with:{}}

```{admonition} Experimental
:class: warning

Always prefer the canonical version. Constant conversion between bases can lead to loss of accuracy, sometimes causing unpredictable behavior.

If you need to "shoot" an entity in a direction, you can still set velocity as a local vector and run `#bs.move:canonical_to_local` before using `#bs.move:apply_vel`.
```

Teleport an entity by its velocity scores, using the local reference frame, while handling collisions.

:Inputs:
  **Execution `as <entities>`**: Entity to move.

  **Scores `@s bs.vel.[x,y,z]`**: Local velocity vector.

  **Function macro**:
  :::{treeview}
  - {nbt}`compound` Arguments
    - {nbt}`number` **scale**: Scalar applied to the output.
    - {nbt}`compound` **with**: Collision settings.
      - {nbt}`bool` **blocks**: Whether the entity should collide with blocks (default: true).
      - {nbt}`bool` {nbt}`string` **entities**: Whether the entity should collide with entities (default: false). Can also be a tag that entities must have.
      - {nbt}`string` **hitbox_shape**: Hitbox type: `interaction` or `collision` (default: `collision`).
      - {nbt}`string` **ignored_blocks**: Blocks to ignore (default: `#bs.hitbox:can_pass_through`).
      - {nbt}`string` **ignored_entities**: Entities to ignore (default: `#bs.hitbox:intangible`).
      - {nbt}`string` **on_collision**: Command to run when a collision occurs, used to resolve the collision (default: `function #bs.move:callback/bounce`).
  :::

:Outputs:
  **State**: Entity is teleported according to its local velocity scores.
`````

::::
:::::

```{admonition} Collision / Interaction Shape
:class: info
- **Collision Shape**: Defines the physical boundaries of a block that entities cannot pass through. It determines where an entity will stop when moving towards the block.
- **Interaction Shape**: Defines the area where the player can interact with or break the block. This includes actions such as right-clicking to open a GUI (e.g., chests, furnaces) or mining the block. Some blocks have an interaction shape but no collision, such as crops or scaffolding.
```

*Example: Move a cube (block_display) by its velocity scores (uses an interaction as the hitbox):*

```mcfunction
# Once
summon minecraft:block_display ~ ~ ~ {block_state:{Name:"stone"},teleport_duration:3,transformation:[1f,0f,0f,-0.5f,0f,1f,0f,0f,0f,0f,1f,-0.5f,0f,0f,0f,1f],Passengers:[{id:"minecraft:interaction",width:1f,height:1f}]}
scoreboard players set @e[type=minecraft:block_display] bs.vel.x 100
scoreboard players set @e[type=minecraft:block_display] bs.vel.y 20
scoreboard players set @e[type=minecraft:block_display] bs.vel.z 50

# In a loop
execute as @e[type=minecraft:block_display] run function #bs.move:apply_vel {scale:0.001,with:{}}

# Choose between multiple collision behaviors
execute as @e[type=minecraft:block_display] run function #bs.move:apply_vel {scale:0.001,with:{on_collision:"function #bs.move:callback/bounce"}}
execute as @e[type=minecraft:block_display] run function #bs.move:apply_vel {scale:0.001,with:{on_collision:"function #bs.move:callback/damped_bounce"}}
execute as @e[type=minecraft:block_display] run function #bs.move:apply_vel {scale:0.001,with:{on_collision:"function #bs.move:callback/slide"}}
execute as @e[type=minecraft:block_display] run function #bs.move:apply_vel {scale:0.001,with:{on_collision:"function #bs.move:callback/stick"}}
```

```{admonition} Performance Tip
:class: tip

Although this system doesn't set specific limits, it's important to note that performance is influenced by both the speed and size of the entity.
```

> **Credits**: Aksiome

---

### Canonical to Local

```{function} #bs.move:canonical_to_local

Convert a canonical velocity (using the relative reference frame) into a local velocity (using the local reference frame).

:Inputs:
  **Execution `rotated as <entity>` or `rotated <h> <v>`**: Rotation used for the conversion.

  **Scores `@s bs.vel.[x,y,z]`**: Velocity to convert.

:Outputs:
  **Scores `@s bs.vel.[x,y,z]`**: Converted velocity.
```

```{admonition} Local Velocity... 🥶 What's this?
:class: dropdown

Unlike relative velocity (canonical), this reference frame considers the entity's rotation. Therefore, when the parent entity rotates, the child entity rotates around it. For those familiar with Minecraft commands, local coordinates are available through the `^` symbol.
```

> **Credits**: Aksiome

---

### Local to Canonical

```{function} #bs.move:local_to_canonical

Convert a local velocity (using the local reference frame) into a canonical velocity (using the relative reference frame).

:Inputs:
  **Execution `rotated as <entity>` or `rotated <h> <v>`**: Rotation used for the conversion.

  **Scores `@s bs.vel.[x,y,z]`**: Velocity to convert.

:Outputs:
  **Scores `@s bs.vel.[x,y,z]`**: Converted velocity.
```

```{admonition} Local Velocity... 🥶 What's this?
:class: dropdown

Unlike relative velocity (canonical), this reference frame considers the entity's rotation. Therefore, when the parent entity rotates, the child entity rotates around it. For those familiar with Minecraft commands, local coordinates are available through the `^` symbol.
```

> **Credits**: Aksiome

---

### Set Motion

```{function} #bs.move:set_motion {scale:<scaling>}

Set the motion NBT of an entity using velocity scores.

:Inputs:
  **Execution `as <entities>`**: Entity to move.

  **Scores `@s bs.vel.[x,y,z]`**: Velocity vector.

  **Function macro**:
  :::{treeview}
  - {nbt}`compound` Arguments
    - {nbt}`number` **scale**: Scalar applied to the output.
  :::

:Outputs:
  **State**: Motion is applied to the given entity.
```

*Example: Move a pig by its velocity scores:*

```mcfunction
# Once
summon minecraft:pig ~ ~ ~
scoreboard players set @e[type=minecraft:pig] bs.vel.x 50
scoreboard players set @e[type=minecraft:pig] bs.vel.y 25
scoreboard players set @e[type=minecraft:pig] bs.vel.z 0

# In a loop
execute as @e[type=minecraft:pig] run function #bs.move:set_motion {scale:0.001}
```

> **Credits**: Aksiome

---

## 👁️ Predicates

You can find below all predicates available in this module.

---

### Has Velocity?

**`bs.move:has_vel`**

Determine if an entity has a nonzero velocity score.

> **Credits**: Aksiome

---

## 🎓 Custom Collisions

This module allows you to customize collision behaviors according to your specific needs.

---

By modifying the `on_collision` input key, you have the freedom to specify the function that triggers upon collision. However, managing the resolution yourself can be quite challenging. This is why Bookshelf provides several predefined functions:

:::{list-table}
  *   - `#bs.move:callback/bounce`
      - The entity will bounce on the collision surface.
  *   - `#bs.move:callback/damped_bounce`
      - The entity speed is reduced by 2 on each bounce.
  *   - `#bs.move:callback/slide`
      - The entity will stick and slide along the collision surface.
  *   - `#bs.move:callback/stick`
      - The entity will stop and stick to the collision surface.
:::

### How It Works?

Upon collision, you have the freedom to update both the velocity score that will be used in the next tick `@s bs.vel.[x,y,z]` and the remaining velocity `$move.vel.[x,y,z] bs.lambda`. Since the module will attempt to continue moving based on the remaining velocity, it's crucial to avoid introducing a race condition.

```{admonition} Velocity Scaling
:class: warning
Remaining velocity scores are stored as scaled integers, but the scaling factor may change without breaking compatibility.

To ensure stability, always manipulate these values independently of the scaling factor.
```

The simplest collision resolution is to stop the movement.

*`#bs.move:callback/stick`*
```mcfunction
# set all components to 0 to cancel the movement
execute store result score $move.vel.x bs.lambda run scoreboard players set @s bs.vel.x 0
execute store result score $move.vel.y bs.lambda run scoreboard players set @s bs.vel.y 0
execute store result score $move.vel.z bs.lambda run scoreboard players set @s bs.vel.z 0
```

For sliding, we need to cancel the velocity on the axis that was hit and continue traveling the remaining distance.

*`#bs.move:callback/slide`*
```mcfunction
# set a component to 0 depending on the surface that was hit
execute if score $move.hit_face bs.lambda matches 4..5 store result score $move.vel.x bs.lambda run scoreboard players set @s bs.vel.x 0
execute if score $move.hit_face bs.lambda matches 0..1 store result score $move.vel.y bs.lambda run scoreboard players set @s bs.vel.y 0
execute if score $move.hit_face bs.lambda matches 2..3 store result score $move.vel.z bs.lambda run scoreboard players set @s bs.vel.z 0
```

To simplify the creation of these behaviors, there's no need to handle a local velocity directly. The vector is automatically converted before and after the collision resolution. If you need help with custom collisions, you can ask us on our [discord server](https://discord.gg/MkXytNjmBt)!

---

```{include} ../_templates/comments.md
```