# Spawn Over Distance

Menu Path: **Spawn > Custom > Spawn Over Distance**

The **Spawn Over Distance** Block calculates the displacement of a position relative to the previous frame's value. Depending on this size of the displacement and the **Rate Per Unit** property, the system spawns a particle.

<video src="Images/Block-SpawnOverDistanceExample.mp4" title="Left: A Spawn Over Distance block and an Initialize Particle block are connected. The Spawn Over Distance block spawns 10 instances for every unit. A Change Space (Position) block whose Target Space is World is connected to the Spawn Over Distance block. Right: As a magic lamp glides smoothly through the scene view, it emits a continuous trail of particles based on the distance it travels. The particles are spawned at regular intervals along the lamp's motion path, forming a fluid, glowing trail. " width="320" height="auto" autoplay="true" loop="true" controls></video>

## Block compatibility

This Block is compatible with the following Contexts:

- [Spawn](Context-Spawn.md)

## Block properties

| **Input**              | **Type** | **Description**                                              |
| ---------------------- | -------- | ------------------------------------------------------------ |
| **Position**           | Vector3  | The reference position to use to check whether to spawn a particle or not. The system automatically stores this value in the position spawn state attribute. It stores the previous value in the oldPosition spawn state attribute. |
| **Rate per Unit**      | float    | The number of particles to spawn per unit of displacement.   |
| **Velocity Threshold** | float    | The maximum velocity to consider for spawning. If the position moves faster than this threshold, the Block does not spawn anymore particles. |

## Remarks

This Block uses a VFXSpawnerCallback interface and you can use it as a reference to create your own implementation. The implementation for this Block is in **com.unity.visualeffectgraph > Runtime > CustomSpawners > SpawnOverDistance.cs**.