Levels of detail: the source

since 0.7.0 Scene and geometry
Open the live demo · Read the guide · View on GitHub
Regions the guide quotes: parts (line 22), asset (line 53), instantiate (line 69), selection (line 81), check (line 86).
1/// Three sphere meshes, packed into one `ModelAsset` with levels of detail and
2/// selected by their projected screen size.
3library;

5import 'package:flutter3d/flutter3d.dart';
6import 'package:flutter3d_showcase/src/demo/demo.dart';
7import 'package:vector_math/vector_math.dart';

9final class LevelOfDetailDemo extends ShowcaseDemo {
late final LodGroup _group;

@override
void configureView(DemoContext context) {
  context.orbit
    ..distance = 8.0
    ..pitch = 0.18
    ..yaw = 0.35;
}

@override
Scene build(DemoContext context) {
  final List<(String, SphereShape, Vector4)> definitions =
      <(String, SphereShape, Vector4)>[
        (
          'fine',
          const SphereShape(radius: 1.6, segments: 48, rings: 24),
          Vector4(0.16, 0.68, 0.92, 1.0),
        ),
        (
          'medium',
          const SphereShape(radius: 1.6, segments: 20, rings: 10),
          Vector4(0.95, 0.62, 0.16, 1.0),
        ),
        (
          'coarse',
          const SphereShape(radius: 1.6, segments: 8, rings: 4),
          Vector4(0.84, 0.24, 0.28, 1.0),
        ),
      ];
  final List<ModelPart> parts = <ModelPart>[
    for (final (String name, SphereShape shape, Vector4 color) in definitions)
      ModelPart(
        mesh: DeviceMesh.upload(context.device, shape.build()),
        material: Material(
          name: '$name material',
          baseColor: color,
          roughness: 0.52,
        ),
        name: name,
      ),
  ];

  final ModelNode node = ModelNode(
    name: 'sphere lod',
    surfaces: const <int>[0],
    lods: const <ModelLod>[
      ModelLod(surfaceIndices: <int>[1], maxScreenFraction: 0.34),
      ModelLod(surfaceIndices: <int>[2], maxScreenFraction: 0.15),
    ],
  );
  final ModelAsset asset = ModelAsset(
    name: 'sphere lod asset',
    parts: parts,
    nodes: <ModelNode>[node],
    roots: const <int>[0],
    localBounds: parts.first.mesh.bounds,
  );

  final Scene scene = Scene()
    ..ambientColor = Vector3(0.42, 0.5, 0.68)
    ..ambientIntensity = 0.14
    ..add(
      LightNode(name: 'sun', intensity: 3.2)
        ..setLocalForward(Vector3(-0.46, -0.82, -0.34)),
    );
  asset.instantiate(scene);
  _group = scene.lodGroups.single;
  return scene;
}

double _screenFraction(Scene scene) =>
    _group.screenFraction(scene.cameras.single);

@override
void verify(Scene scene, FrameResult frame) {
  final int visibleLevels = _group.levels
      .where((LodLevel level) => level.node.visible)
      .length;
  final double fraction = _screenFraction(scene);
  if (scene.lodGroups.single != _group ||
      _group.activeLevel < 0 ||
      _group.activeLevel >= _group.levels.length ||
      visibleLevels != 1 ||
      fraction <= 0.0 ||
      frame.drawCalls < 1) {
    throw StateError('the LOD group did not select one visible mesh');
  }
}
99}