Emitters

Shapes

You can have access to different "shapes" of emitters that will decide where your particles will initially spawn.

The editor has these built-in for you to use:

Box

Sphere

Ring

Cone

Model

Default emitter properties

In all emitters you can find these same parameters. You can randomize all of them and animate the rate and rate over distance with curves over the emitter duration

Loop

Whether the emitter should restart after finishing

Destroy on end

Whether the emitter should be destroyed after finishing. Only works if loop is disabled

Duration

How long the emitter should run for

Delay

How many seconds before the emitter starts running

Rate

Will spawn the set amount of particles in a rate per second, so a value of one means 1 particle/sec (any value below 1 is clamped to 0)

Rate over distance

Will spawn the set amount of particles evenly every 100 units the emitter's GameObject moves

Burst

Will spawn the set amount of particles at the start of the emitter duration

Custom emitters

You can create custom emitters by inheriting ParticleEmitter

using System;

namespace Sandbox;

/// <summary>
/// Emits particles from a triangular shape, lying in the local XY plane.
/// </summary>
public sealed class CustomEmitter : ParticleEmitter
{
	/// <summary>
	/// The size (in units) of the triangle, from its centre to a corner.
	/// </summary>
	[Property, Range( 0, 500 ), Group( "Shape" )] public float Size { get; set; } = 50.0f;

	/// <summary>
	/// If true, particles spawn along the edges of the triangle. Otherwise they fill it.
	/// </summary>
	[Property, Group( "Shape" )] public bool OnEdge { get; set; } = false;

	public override bool Emit( ParticleEffect target )
	{
		// The three corners of an equilateral triangle centred on the origin,
		// pointing up the local +Y axis.
		var a = new Vector3( 0.0f, 1.0f, 0.0f );
		var b = new Vector3( 0.866f, -0.5f, 0.0f );
		var c = new Vector3( -0.866f, -0.5f, 0.0f );

		Vector3 localPos;

		if ( OnEdge )
		{
			// Pick a random edge, then a random point along it.
			var t = Random.Shared.Float( 0, 1 );
			localPos = Random.Shared.Int( 0, 2 ) switch
			{
				0 => Vector3.Lerp( a, b, t ),
				1 => Vector3.Lerp( b, c, t ),
				_ => Vector3.Lerp( c, a, t ),
			};
		}
		else
		{
			// Uniform random point inside the triangle, using barycentric coordinates.
			var r1 = Random.Shared.Float( 0, 1 );
			var r2 = Random.Shared.Float( 0, 1 );
			if ( r1 + r2 > 1.0f )
			{
				r1 = 1.0f - r1;
				r2 = 1.0f - r2;
			}

			localPos = a + r1 * (b - a) + r2 * (c - a);
		}

		var worldPos = WorldTransform.PointToWorld( localPos * Size );

		var p = target.Emit( worldPos, Delta );
		return p is not null;
	}
}

With this example component you can have a triangle shape to emit your particles