Texture transform: the source

since 0.7.0 Formats and I/O
Open the live demo · Read the guide · View on GitHub
Regions the guide quotes: checker (line 19), transform (line 40), check (line 71).
1/// `withTextureTransform`: `KHR_texture_transform`, applied to a mesh's own
2/// texture coordinates.
3///
4/// Quoted by `texture_transform.md` and shown whole in the Source tab.
5library;

7import 'dart:typed_data';

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

13final class TextureTransformDemo extends ShowcaseDemo {
late final MeshData _plain;
late final MeshData _moved;

@override
Scene build(DemoContext context) {
  // An 8x8 checker, small enough that scaling the transform below by
  // four makes the tiling obvious.
  final pixels = Uint8List(8 * 8 * 4);
  for (var y = 0; y < 8; y++) {
    for (var x = 0; x < 8; x++) {
      final lit = ((x ~/ 2) + (y ~/ 2)).isEven;
      final o = (y * 8 + x) * 4;
      final value = lit ? 235 : 25;
      pixels[o] = value;
      pixels[o + 1] = value;
      pixels[o + 2] = value;
      pixels[o + 3] = 255;
    }
  }
  final albedo = context.device.createTextureFromPixels(
    width: 8,
    height: 8,
    format: TextureFormat.r8g8b8a8UNormInt,
    pixels: ByteData.sublistView(pixels),
  );

  // `KHR_texture_transform`'s own order: scale, then rotate, then move.
  // Scaling by four here tiles the checker four times across the plane
  // instead of stretching one copy of it across the whole surface.
  _plain = PlaneShape(width: 2, depth: 2).build();
  final transform = TextureTransform(scale: Vector2(4.0, 4.0));
  _moved = withTextureTransform(_plain, transform);

  return Scene()
    ..add(
      MeshNode(
        DeviceMesh.upload(context.device, _moved),
        Material(albedo: albedo, roughness: 0.8, doubleSided: true),
        name: 'floor',
      ),
    )
    ..add(
      LightNode(name: 'sun', intensity: 3.0)
        ..setLocalForward(Vector3(-0.4, -1.0, -0.3)),
    );
}

@override
void configureView(DemoContext context) {
  context.orbit
    ..distance = 3.0
    ..pitch = 0.9
    ..yaw = 0.4;
}

@override
void verify(Scene scene, FrameResult frame) {
  final layout = _plain.layout;
  final stride = layout.floatsPerVertex;
  final uvOffset = layout.floatOffsetOf(VertexLayout.texcoord.name);
  // The plane's corner at U=1 should come back at U=4, the same
  // arithmetic checked independently of whatever `withTextureTransform`
  // did internally.
  final cornerOffset = stride + uvOffset;
  final sourceU = _plain.vertices[cornerOffset];
  final movedU = _moved.vertices[cornerOffset];
  if ((movedU - sourceU * 4.0).abs() > 1e-6 || sourceU == 0.0) {
    throw StateError('the transform did not scale U by four');
  }
  if (_moved.vertices.length != _plain.vertices.length) {
    throw StateError('the transform changed the vertex count');
  }
  if (frame.drawCalls < 1) {
    throw StateError('the floor was not drawn');
  }
}
90}