Orbit: the source

since 0.7.0 Views, picking and input
Open the live demo · Read the guide · View on GitHub
Regions the guide quotes: bounds (line 35), frame (line 40), swing (line 43), advance (line 53).
1/// Framing a model automatically, and swinging the view to a new angle
2/// instead of jumping to it.
3///
4/// Quoted by `orbit_controller.md` and shown whole in the Source tab.
5library;

7import 'dart:math' as math;

9import 'package:flutter3d/flutter3d.dart';
10import 'package:flutter3d_showcase/src/demo/demo.dart';
11import 'package:vector_math/vector_math.dart';

13final class OrbitControllerDemo extends ShowcaseDemo {
late final Aabb3 _bounds;
late final OrbitController _orbit;
late final double _startYaw;

@override
Scene build(DemoContext context) {
  _orbit = context.orbit;
  final Material stone = Material(
    name: 'stone',
    baseColor: Vector4(0.6, 0.66, 0.7, 1.0),
    roughness: 0.7,
  );
  final MeshNode box = MeshNode(
    DeviceMesh.upload(
      context.device,
      CuboidShape(size: Vector3(1.0, 2.0, 1.0)).build(),
    ),
    stone,
    name: 'box',
  );

  _bounds = Aabb3.centerAndHalfExtents(
    Vector3.zero(),
    Vector3(0.5, 1.0, 0.5),
  );

  context.orbit.frameBounds(_bounds);

  _startYaw = context.orbit.yaw;
  context.orbit.animateTo(yaw: context.orbit.yaw + math.pi, seconds: 1.2);

  return Scene()
    ..add(box)
    ..add(
      LightNode(name: 'sun', intensity: 3.0)
        ..setLocalForward(Vector3(-0.4, -1.0, -0.3)),
    );
}

@override
void update(DemoContext context, double dt) {
  context.orbit.advance(dt);
}

@override
List<DemoControl> controls(DemoContext context) => <DemoControl>[
  ToggleControl(
    'Swing to the other side',
    value: () => context.orbit.isTurning,
    onChanged: (bool _) =>
        context.orbit.animateTo(yaw: context.orbit.yaw + math.pi),
  ),
];

@override
void verify(Scene scene, FrameResult frame) {
  if (frame.drawCalls < 1) {
    throw StateError('the box was not drawn');
  }
  // frameBounds places the camera at radius / sin(fov / 2) * margin, using
  // its own default field of view and margin. Recomputing that formula for
  // this box's own radius has to land on the distance the orbit actually
  // holds.
  final Vector3 extent = (_bounds.max - _bounds.min)..scale(0.5);
  final double radius = math.max(extent.length, 1e-4);
  final double expected = radius / math.sin(math.pi / 4 * 0.5) * 1.25;
  if ((_orbit.distance - expected).abs() > 1e-6) {
    throw StateError(
      'frameBounds put the camera at ${_orbit.distance}, expected $expected',
    );
  }
  // The camera also spent one frame turning towards the other side, so its
  // yaw must have moved away from wherever frameBounds first pointed it,
  // and the turn must still be in flight after a sixtieth of a second of a
  // 1.2 second swing.
  if (_orbit.yaw == _startYaw || !_orbit.isTurning) {
    throw StateError('advance did not step the turn animateTo started');
  }
}
93}