Glass that shows the scene: the source

since 0.8.0 Shading and materials
Open the live demo · Read the guide · View on GitHub
Regions the guide quotes: wall (line 38), glass (line 66), live (line 112).
1/// A pane of glass in front of a striped wall, showing the wall through it.
2///
3/// Quoted by `transmission.md` and shown whole in the Source tab.
4library;

6import 'dart:math' as math;

8import 'package:flutter3d/flutter3d.dart';
9import 'package:flutter3d_showcase/src/demo/demo.dart';
10import 'package:vector_math/vector_math.dart';

12final class TransmissionDemo extends ShowcaseDemo {
double transmission = 1.0;
double roughness = 0.0;
double thickness = 0.9;
double ior = 1.5;

late final Material _pane;
late final Material _ball;

@override
void configureView(DemoContext context) {
  context.orbit
    ..distance = 2.6
    ..yaw = 0.0
    ..pitch = 0.0;
}

@override
Scene build(DemoContext context) {
  final Quaternion upright = Quaternion.axisAngle(
    Vector3(1.0, 0.0, 0.0),
    math.pi / 2,
  );
  Material flat(Vector4 colour) =>
      Material(lighting: LightingModel.unlit, baseColor: colour);

  final DeviceMesh half = DeviceMesh.upload(
    context.device,
    const PlaneShape(width: 3.0, depth: 4.0).build(),
  );
  final DeviceMesh stripe = DeviceMesh.upload(
    context.device,
    const PlaneShape(width: 0.08, depth: 4.0).build(),
  );
  final Scene scene = Scene()
    ..ambientIntensity = 0.2
    ..add(
      MeshNode(half, flat(Vector4(0.8, 0.1, 0.1, 1.0)), name: 'red wall')
        ..setRotation(upright)
        ..setPosition(-1.5, 0.0, -2.0),
    )
    ..add(
      MeshNode(half, flat(Vector4(0.1, 0.2, 0.9, 1.0)), name: 'blue wall')
        ..setRotation(upright)
        ..setPosition(1.5, 0.0, -2.0),
    );
  for (var i = 0; i < 9; i++) {
    scene.add(
      MeshNode(stripe, flat(Vector4(0.95, 0.95, 0.9, 1.0)), name: 'stripe')
        ..setRotation(upright)
        ..setPosition(-2.0 + i * 0.5, 0.0, -1.98),
    );
  }

  Material glass(String name, {required double thickness}) => Material(
    name: name,
    lighting: LightingModel.pbrLayered,
    baseColor: Vector4(1.0, 1.0, 1.0, 1.0),
    roughness: roughness,
    doubleSided: true,
    extensions: MaterialExtensions(
      transmission: transmission,
      thickness: thickness,
      ior: ior,
    ),
  );
  _pane = glass('pane', thickness: 0.0);
  _ball = glass('ball', thickness: thickness);
  scene
    ..add(
      MeshNode(
          DeviceMesh.upload(
            context.device,
            const PlaneShape(width: 0.9, depth: 1.4).build(),
          ),
          _pane,
          name: 'pane',
        )
        ..setRotation(upright)
        ..setPosition(-0.6, 0.0, 0.0),
    )
    ..add(
      MeshNode(
        DeviceMesh.upload(
          context.device,
          SphereShape(radius: 0.45, segments: 48, rings: 24).build(),
        ),
        _ball,
        name: 'ball',
      )..setPosition(0.6, 0.0, 0.0),
    )
    ..add(
      LightNode(name: 'sun', intensity: 3.0)
        ..setLocalForward(Vector3(-0.3, -0.6, -1.0).normalized()),
    );
  return scene;
}

@override
void update(DemoContext context, double dt) {
  for (final (Material material, double depth) in <(Material, double)>[
    (_pane, 0.0),
    (_ball, thickness),
  ]) {
    material
      ..roughness = roughness
      ..extensions = MaterialExtensions(
        transmission: transmission,
        thickness: depth,
        ior: ior,
      );
  }
}

@override
List<DemoControl> controls(DemoContext context) => <DemoControl>[
  SliderControl(
    'Transmission',
    min: 0,
    max: 1,
    value: () => transmission,
    onChanged: (double v) => transmission = v,
  ),
  SliderControl(
    'Roughness',
    min: 0,
    max: 1,
    value: () => roughness,
    onChanged: (double v) => roughness = v,
  ),
  SliderControl(
    'Thickness',
    min: 0,
    max: 1.5,
    value: () => thickness,
    onChanged: (double v) => thickness = v,
    // In the mesh's own units, as glTF measures it, not metres.
    format: (double v) => '${v.toStringAsFixed(2)} units',
  ),
  SliderControl(
    'Index of refraction',
    min: 1.0,
    max: 2.4,
    value: () => ior,
    onChanged: (double v) => ior = v,
    format: (double v) => v.toStringAsFixed(2),
  ),
];

@override
void verify(Scene scene, FrameResult frame) {
  // A pane with no transmission is opaque, drawn in one pass as it always
  // was; at an index of 1.5 it is ordinary metal-rough, and at another
  // index it keeps that index's reflectance.
  if (transmission <= 0.0) return;
  final Set<String> ran = <String>{
    for (final FramePass pass in frame.passes) pass.name,
  };
  if (!ran.contains('scene colour copy')) {
    throw StateError(
      'the glass is in the frame but the scene was not copied',
    );
  }
  final FramePass? glass = frame.passes
      .where((FramePass p) => p.name == 'transparent')
      .firstOrNull;
  if (glass == null || glass.drawCalls < 1) {
    throw StateError('the pass that draws the glass drew nothing');
  }
}
182}