Particle Systems

Fire, smoke, sparks, magic, rain, explosions — all of it comes from the Particle System, a modular emitter modelled after Unity's. You start with an emitter and switch on modules — emission, shape, colour-over-lifetime, velocity, size, texture animation — each shaping the particles a little more.

The Particle System playing in the editor with the module inspector and preview controls.

The emitter and its modules

Add a Particle System from Add Behaviour and it starts emitting immediately in the editor, with a preview overlay (Play / Pause / Stop, playback speed and a scrubber) in the scene view.

The top of the inspector is the System block — the properties every particle is born with:

Duration and Loop — the length of one emission cycle and whether it repeats.
Start Lifetime / Start Speed / Start Size / Start Rotation / Start Color — initial values. Each is a value selector: a constant, a random range, or a curve/gradient over the cycle.
Gravity Scale, Max Particles, Simulation Space (Local follows the emitter, World leaves particles behind), and Play On Awake.

Below that sit the toggleable modules, each with an enable checkbox:

Module	Effect
Emission	Rate-per-second plus timed Bursts.
Shape	Where particles spawn: `Circle`, `Rectangle` or `Edge`.
Velocity / Force / Limit Velocity over Lifetime	Push, drag and steer particles as they age.
Color / Size / Rotation over Lifetime	Fade, grow and spin over each particle's life.
Color / Size / Rotation by Speed	Modulate by how fast a particle is moving.
Texture Animation	Flipbook the particle sprite from a sheet or sprite list.
Renderer	Draw mode (`Chunk` batches, `Individual` allows per-particle material) and sort order.

Value selectors and gradients

The recurring pattern is the value selector — wherever you see a property like Start Size or a lifetime curve, it can be a constant, a random between two values, or a curve (float) / gradient (colour) sampled over the particle's normalized age. This is what makes a flame fade from white to orange to transparent, or embers shrink as they rise.

Controlling it from AngelScript

using namespace CometEngine;
using namespace CometEngine::ParticleSystemModule;

class Explosion : CometBehaviour
{
    void Start()
    {
        ParticleSystem particles = ParticleSystem::Get(entity);
        particles.loop = false;
        particles.maxParticles = 500;

        // Configure emission with a one-shot burst of debris.
        ParticlePropertyEmission emission = particles.emission;
        emission.enabled = true;

        Burst burst;
        burst.time = 0.0F;
        burst.probability = 1.0F;
        burst.count.constant = 60;
        emission.AddBurst(burst);

        particles.Play();
    }

    void Update()
    {
        ParticleSystem particles = ParticleSystem::Get(entity);
        // Emit a puff of smoke on demand.
        if (Input::GetKeyDown(KeyCode::SPACE))
        {
            particles.Emit(20);
        }
    }
}

Play(), Pause(), Stop(), Clear() and Emit(count) drive playback; Simulate(time, restart) fast-forwards the simulation (handy for pre-warming an effect so it looks established the instant it appears). Read-only isPlaying, isEmitting, particleCount and isAlive report state.

[!TIP] simulationSpace = ParticleSystemSimulationSpace::WORLD is the difference between a torch flame that drags a trail as the torch moves (World) and one that stays glued to the torch (Local). Pick per effect.

Building a fire effect

The classic recipe, all in the inspector:

Shape → small Circle at the base.
Start Color → bright yellow; Color over Lifetime → gradient yellow → orange → transparent.
Start Size → medium; Size over Lifetime → curve shrinking to zero.
Velocity over Lifetime → upward, with a little turbulence via the random-between mode.
Emission → a steady rate, no bursts.
Renderer → an additive material so overlapping particles glow.

UI particles

Need particles inside a UI canvas — confetti on a victory screen, sparkles on a button? Use UI Particle System instead. It's the same module set but renders in the UI layer under a RectTransform, so it respects canvas sorting and masks. See the UI tutorial for the canvas basics.

Where to go next

Trigger a burst from an animation event, attach one to a networked spawn, or light it dramatically with 2D lights.