A burst that lights the room

since 0.7.0 Physics and particles

Open the live demo · Read the source · View on GitHub

Before a burst could carry a light source, an explosion or a muzzle flash cast no light however bright its particles were painted. ParticleSystem.burst takes an optional source, and a LightEmitter passed there is fed by the burst's own particles from the instant they appear.

Step 1: One argument on an ordinary burst #

Nothing about the burst itself is different: the same count, the same emitter, the same lifetime a plain spark burst would use. The only new thing is source.

// Nothing above this differs from an ordinary burst. `source` is the
// whole of what makes it a light: a `LightEmitter` passed here has its
// glow fed by exactly these particles, for as long as they live.
_flashEffect = ParticleEffect(
  count: 60,
  emitter: const SphereEmitter(speed: Range(2.0, 5.0)),
  lifetime: const Range(0.2, 0.4),
  size: const Range(0.05, 0.09),
  color: Vector4(1.0, 0.85, 0.5, 1.0),
);
_particles.burst(_flashEffect, Vector3.zero(), source: _flash);

Step 2: Follow it while it lasts #

The glow fades on its own once the last particle of the burst has died, so the light needs no cleanup: it is measured every step, for exactly as long as there is anything left to measure.

final ParticleGlow glow = _flash.glow;
if (glow.located) {
  _glow.setPositionFrom(glow.centre);
  _glow.intensity = glow.power * 0.6;
}

Step 3: What "lit" means here #

A burst that never reaches a light emitter never updates a ParticleGlow, so the check on this page is direct: after one step, the flash should have counted particles and produced a positive amount of light.

if (_flash.glow.count == 0 || _flash.glow.power <= 0.0) {
  throw StateError('the burst should have lit its own flash');
}

Note. This is the same mechanism the standing-emission torch on the particle-lights page uses. The difference is only in how the particles arrive: all at once here, one sub-step's worth at a time there.