Flickering lights

since 0.4.0 or earlier Simulation, audio and XR

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

A torch's flame and the light it casts have to agree, or a fire that dances while its light stays flat reads as fake. LightFixture owns one brightness number and drives both from it.

Step 1: Make a fixture #

LightFixture names the level light it drives and a LightBehaviour. FlameFlicker is two unrelated sine waves plus a slow one, deliberately computed from the clock rather than from randomness, so the same moment looks the same after a reload.

late LightFixture _fixture = LightFixture(
  name: 'torch',
  light: 'torch',
  behaviour: const FlameFlicker(),
);

Step 2: Step it and read its brightness #

Each frame, the fixture is stepped like anything else in the simulation, and its brightness drives both the light's intensity and the glow on the torch's own material.

@override
void update(DemoContext context, double dt) {
  _fixture.step(dt);
  _torchLight.intensity = 4.0 * _fixture.brightness;
  _torchMaterial.emissive.setValues(
    _fixture.brightness,
    _fixture.brightness * 0.6,
    _fixture.brightness * 0.2,
  );
}

Switch to "Pulse instead of flicker" and the fixture is rebuilt with PulseLight, a slow smooth swell instead of a flame's jitter.

Step 3: Turn it off #

// Switching the fixture off drops its brightness to zero on the next
// step, whichever behaviour is driving it.
_fixture.enabled = false;
_fixture.step(1 / 60);

A fixture that is switched off reports zero brightness on its very next step, whichever behaviour it was running.