Baking a lightmap

since 0.4.1 Simulation, audio and XR

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

Direct light and its shadows stay dynamic, so a torch can flicker and a door can open. The light that does not move is a wall lighting the floor next to it, and baking that once is cheaper than computing it every frame. Baking a lightmap is two steps: plan where each face lives in the atlas, then gather the light into it.

Step 1: A small level #

A floor and a wall, meeting at a corner, with a point light above them.

final level = Level(
  name: 'closet',
  brushes: <Brush>[
    Brush(centre: Vector3(2, 0, 2), size: Vector3(4, 0.2, 4)),
    Brush(centre: Vector3(2, 2, 0), size: Vector3(4, 4, 0.2)),
  ],
  lights: <LevelLight>[
    LevelLight(position: Vector3(2, 3, 2), intensity: 6.0),
  ],
);

Step 2: Plan the atlas #

LightmapLayout.plan unwraps every visible brush face onto a planar atlas, purely from the level and a chosen density. The baker and the level's own geometry agree on where each face sits without a separate table.

final layout = LightmapLayout.plan(level, texelsPerMetre: 2.0);

Step 3: Bake the light #

LightmapBaker.bake gathers the direct light and its bounces into the planned atlas, seeded so two bakes of the same level are the same bytes.

const baker = LightmapBaker(bounces: 1, samples: 8);
final lightmap = baker.bake(level, layout: layout);
final anyLight = lightmap.pixels.any((int byte) => byte > 0);

The corner where the wall meets the floor picks up light from both, so the map is not left entirely black.

Step 4: See what it baked #

The page shows the atlas itself: each texel of every face of the closet, as bright as the light that reaches it. Slide the light along the closet and the bright patch on the floor follows it; take the bounces to zero and the wall loses what the floor was lending it; lower the samples and the noise shows. Each change is a whole new bake, made when you let go of the slider.

final Level level = Level(
  name: 'closet',
  brushes: <Brush>[
    Brush(centre: Vector3(2, 0, 2), size: Vector3(4, 0.2, 4)),
    Brush(centre: Vector3(2, 2, 0), size: Vector3(4, 4, 0.2)),
  ],
  lights: <LevelLight>[
    LevelLight(position: Vector3(lightX, 3, 2), intensity: 6.0),
  ],
);
final LightmapLayout layout = LightmapLayout.plan(
  level,
  texelsPerMetre: texels,
);
final Lightmap lightmap = LightmapBaker(
  bounces: bounces.round(),
  samples: samples.round(),
).bake(level, layout: layout);