The held item's own pass: the source

since 0.4.0 Scene and geometry
Open the live demo · Read the guide · View on GitHub
Regions the guide quotes: world (line 27), hands (line 60), pass (line 88), motion (line 96), check (line 117).
1/// A held item drawn in its own pass, over the finished world.
2library;

4import 'dart:math' as math;

6import 'package:flutter3d/flutter3d.dart';
7import 'package:flutter3d_showcase/src/demo/demo.dart';
8import 'package:vector_math/vector_math.dart';

10final class ViewModelDemo extends ShowcaseDemo {
double fovDegrees = 48.0;
double _bob = 0.0;

late final CameraNode _handCamera;
late final MeshNode _tool;

@override
void configureView(DemoContext context) {
  context.orbit
    ..distance = 6.0
    ..pitch = 0.2
    ..yaw = 0.4;
}

@override
Scene build(DemoContext context) {
  final Material stone = Material(
    name: 'stone',
    baseColor: Vector4(0.58, 0.56, 0.52, 1.0),
    roughness: 0.82,
  );
  final Scene world = Scene()
    ..ambientColor = Vector3(0.4, 0.46, 0.6)
    ..ambientIntensity = 0.16
    ..add(
      MeshNode(
        DeviceMesh.upload(
          context.device,
          const PlaneShape(width: 20, depth: 20).build(),
        ),
        stone.copy()..doubleSided = true,
        name: 'floor',
      ),
    )
    ..add(
      MeshNode(
        DeviceMesh.upload(
          context.device,
          CuboidShape(size: Vector3(1.4, 2.4, 1.4)).build(),
        ),
        stone,
        name: 'pillar',
      )..setPosition(0.0, 1.2, -3.0),
    )
    ..add(
      LightNode(name: 'sun', intensity: 3.0)
        ..setLocalForward(Vector3(-0.4, -0.8, -0.3)),
    );

  final Scene handsScene = Scene()
    ..add(
      _tool = MeshNode(
        DeviceMesh.upload(
          context.device,
          CuboidShape(size: Vector3(0.12, 0.12, 0.6)).build(),
        ),
        Material(
          name: 'tool',
          baseColor: Vector4(0.66, 0.68, 0.72, 1.0),
          metallic: 0.85,
          roughness: 0.28,
        ),
        name: 'held tool',
      )..setPosition(0.22, -0.2, -0.5),
    )
    ..add(
      LightNode(name: 'hand key', intensity: 2.6)
        ..setLocalForward(Vector3(-0.3, -0.5, -0.8)),
    );
  _handCamera = CameraNode(
    name: 'hand camera',
    projection: PerspectiveProjection(
      fovYRadians: fovDegrees * math.pi / 180.0,
    ),
  );
  handsScene.add(_handCamera);

  context.renderer.addNode(
    ViewModelNode(scene: handsScene, camera: _handCamera),
  );
  return world;
}

@override
void update(DemoContext context, double dt) {
  _bob += dt;
  _tool.setPosition(0.22, -0.2 + math.sin(_bob * 2.4) * 0.02, -0.5);
  _handCamera.projection = PerspectiveProjection(
    fovYRadians: fovDegrees * math.pi / 180.0,
  );
}

@override
List<DemoControl> controls(DemoContext context) => <DemoControl>[
  SliderControl(
    'Hand field of view',
    min: 25,
    max: 90,
    value: () => fovDegrees,
    onChanged: (double value) => fovDegrees = value,
    format: (double value) => '${value.round()} deg',
  ),
];

@override
void verify(Scene scene, FrameResult frame) {
  final bool viewModelRan = frame.passes.any(
    (FramePass pass) => pass.name == 'view model',
  );
  if (!viewModelRan || frame.drawCalls < 2) {
    throw StateError('the view model pass did not draw over the world');
  }
}
124}