Particles

The Particles tool places particle effects into the scene. An effect is a running simulation, not a canned clip: particles are emitted, forces accelerate them, they are integrated, they collide, they age, and they die, one fixed timestep at a time.

Because it is a real simulation, an effect responds to its settings. Raise gravity and the same fire falls; add wind and the same snow drifts. Because the simulation is deterministic, it is also safe to animate — the same frame produces the same image every time it is drawn.

Determinism#

The simulation is pure, fixed-timestep, and seeded. Given a seed and a frame number, the resulting particles are identical on every run, so a shot plays back, scrubs, and exports the same. Each step runs in a fixed order: emit, apply forces, integrate, collide, age, reap. Integration is semi-implicit Euler — each particle's velocity is advanced first, then its position is advanced with that new velocity.

The turbulence that most presets use is curl noise: a divergence-free field, layered over several octaves and evolving over simulation time, which is why particles swirl through it rather than collecting in pockets. The noise is built on an integer hash and pure float arithmetic — no trigonometry — so the field is identical across devices rather than differing in the last bit.

Placing an effect#

An emitter's position is not a buried property of the effect. It is a first-class timeline owner in its own right, with the ordinary transform channels, so it can be driven by the gizmo and keyframed like any other object — an emitter can be flown along a path with the fire still burning at its tip.

Frame-lock#

Effects are stepped against the timeline's frame, not against the wall clock. The consequences are worth knowing:

• Parked on a frame, the field holds. A paused or scrubbed shot shows a frozen, exact field rather than a simulation that keeps running while you work.
• Playing forward, the simulation steps forward. If frames are missed, the effect catches up by stepping through them, up to a limit of twelve.
• Scrubbing back, or jumping far, rebuilds the effect from its birth frame, including its warm-up, up to a cap of twenty seconds of simulation.

The frame rate the simulation steps at is the shot's frame rate.

The Particles panel#

The panel is ordered top to bottom:

• Background — three preset swatches and a colour well setting the canvas background colour. A particle effect is usually judged against its background, so the control is placed with the effect rather than elsewhere.
• Effects in scene — appears once at least one effect is placed. Each effect has a row that selects it and a control that deletes it, and Clear all removes every effect at once. The selected effect expands into the full inspector.
• The inspector — Amount, Size, Speed, and Glow (additive), then four groups: Colors, Emission & Duration, Forces, and Look.
• Custom system… — opens the Custom System builder, which assembles an effect from an emitter shape, rate, lifetime, speed, spread, three forces, and a look, instead of starting from a preset.
• The preset browser — the 23 presets, under a header per category.

Every control is documented in Settings.

What is authorable, and what ships inside a preset#

Most of an effect is editable after it is dropped: its emission, its lifetime, its colours and colour-over-life gradient, its four forces, its render style, and its particle graphics.

Some of what the presets are built from has no control in the panel. It is real, it runs, and it persists with the shot — but it can only be had by choosing a preset that carries it.

Nine properties of a placed effect are keyframable from its timeline row: amount, size, speed, spread, lifetime, gravity, wind, turbulence, and the start colour — alongside the emitter's own transform.

See also#