Generate tangent frames: the source

since 0.7.0 Scene and geometry
Open the live demo · Read the guide · View on GitHub
Regions the guide quotes: undressed (line 23), compare (line 30), bump (line 35), check (line 72).
1/// One torus left with a flat, constant tangent and one with tangents
2/// generated from its UVs, both lit by the same tilted normal map.
3library;

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

9final class TangentsDemo extends ShowcaseDemo {
late final MeshData _flatMesh;
late final MeshData _generatedMesh;

@override
void configureView(DemoContext context) {
  context.orbit
    ..distance = 6.5
    ..pitch = 0.2
    ..yaw = 0.4;
}

@override
Scene build(DemoContext context) {
  final MeshData undressed = const TorusShape(
    radius: 0.85,
    tubeRadius: 0.34,
    segments: 40,
    tubeSegments: 20,
  ).build(layout: VertexLayout.positionNormalTexcoord);

  _flatMesh = undressed.convertedTo(VertexLayout.standard);
  _generatedMesh = undressed.withGeneratedTangents(
    target: VertexLayout.standard,
  );

  final TextureHandle tilt = SolidColorTexture(
    Vector4(0.78, 0.5, 0.86, 1.0),
  ).upload(context.device);
  Material bumpMaterial(String name) => Material(
    name: name,
    baseColor: Vector4(0.6, 0.64, 0.7, 1.0),
    metallic: 0.85,
    roughness: 0.2,
    normal: tilt,
  );

  final Scene scene = Scene()
    ..ambientColor = Vector3(0.4, 0.48, 0.64)
    ..ambientIntensity = 0.14
    ..add(
      MeshNode(
        DeviceMesh.upload(context.device, _flatMesh),
        bumpMaterial('flat tangent'),
        name: 'flat',
      )..setPosition(-1.3, 1.0, 0.0),
    )
    ..add(
      MeshNode(
        DeviceMesh.upload(context.device, _generatedMesh),
        bumpMaterial('generated tangent'),
        name: 'generated',
      )..setPosition(1.3, 1.0, 0.0),
    )
    ..add(
      LightNode(name: 'key', intensity: 3.4)
        ..setLocalForward(Vector3(-0.4, -0.7, -0.5)),
    );
  return scene;
}

@override
void verify(Scene scene, FrameResult frame) {
  final int stride = VertexLayout.standard.floatsPerVertex;
  final int tangentOffset = VertexLayout.standard.floatOffsetOf(
    VertexLayout.tangent.name,
  );
  bool tangentVaries(MeshData mesh) {
    double? firstX;
    for (var v = 0; v < mesh.vertexCount; v++) {
      final double x = mesh.vertices[v * stride + tangentOffset];
      firstX ??= x;
      if ((x - firstX).abs() > 1e-4) return true;
    }
    return false;
  }

  if (tangentVaries(_flatMesh) ||
      !tangentVaries(_generatedMesh) ||
      frame.drawCalls < 2) {
    throw StateError('the generated tangents did not follow the surface');
  }
}
92}