KTX2 and Basis textures: the source

since 0.4.2 Formats and I/O
Open the live demo · Read the guide · View on GitHub
Regions the guide quotes: bitstream (line 21), parse (line 36), upload (line 39), check (line 65).
1/// Reading a KTX2 container that carries Basis Universal ETC1S pixels, and
2/// putting the transcoded texture on a cube.
3///
4/// Quoted by `ktx2.md` and shown whole in the Source tab.
5library;

7import 'dart:convert';
8import 'dart:typed_data';

10import 'package:flutter3d/flutter3d.dart' hide Ktx2Texture;
11// The engine's own `Ktx2Texture` (from `flutter3d/flutter3d.dart`) answers
12// a `TextureFormat`, already resolved against a device. This page reads
13// the container itself, which answers the file's own `vkFormat`.
14import 'package:flutter3d_core/formats.dart' show Ktx2Texture, VkFormat;
15import 'package:flutter3d_showcase/src/demo/demo.dart';
16import 'package:vector_math/vector_math.dart';

18final class Ktx2Demo extends ShowcaseDemo {
late final Ktx2Texture _texture;

// An 8x8 image, four flat-coloured quadrants, encoded by a real build of
// `basisu`. `vkFormat` is left undefined, KTX2's own way of saying "these
// pixels are Basis Universal", with the actual flavour named in the
// container's data format descriptor.
static const String _fixtureBase64 =
    'q0tUWCAyMLsNChoKAAAAAAEAAAAIAAAACAAAAAAAAAAAAAAAAQAAAAEAAAABAAAAaAAAACw'
    'AAACUAAAAJAAAALgAAAAAAAAAkQAAAAAAAABJAQAAAAAAAAIAAAAAAAAAAAAAAAAAAAAsA'
    'AAAAAAAAAIAKACjAQEAAwMAAAgAAAAAAAAAAAA/AAAAAAAAAAAA/////x8AAABLVFh3cml'
    '0ZXIAQmFzaXMgVW5pdmVyc2FsIDIuNTAAAAQABAAsAAAAEQAAACwAAAAAAAAAAAAAAAAAA'
    'AACAAAAAAAAAAAAAAAgQEQAAAAAAAgjRAATAQAAAAAASAIDwASAAAAAAADiAGACAAAAAAA'
    'AATkjAKyqUlWtqqqqrKqqqlJVVVUFAMFEAAAAAAAA8l+NAJgBAAAAAABAQgkQIUAAAAAAU'
    'pgiAJgAAAAAAABAAAEEEw==';

@override
Scene build(DemoContext context) {
  final bytes = base64Decode(_fixtureBase64.replaceAll('\n', ''));
  _texture = Ktx2Texture.parse(bytes);

  // The level this reader hands back is already plain RGBA8, so it goes
  // straight onto a device texture the same way any other decoded image
  // would.
  final albedo = context.device.createTextureFromPixels(
    width: _texture.pixelWidth,
    height: _texture.pixelHeight,
    format: TextureFormat.r8g8b8a8UNormInt,
    pixels: _texture.levels.first,
  );

  return Scene()
    ..add(
      MeshNode(
        DeviceMesh.upload(context.device, CuboidShape().build()),
        Material(albedo: albedo, roughness: 0.7),
        name: 'block',
      ),
    )
    ..add(
      LightNode(name: 'sun', intensity: 3.0)
        ..setLocalForward(Vector3(-0.4, -1.0, -0.3)),
    );
}

@override
void verify(Scene scene, FrameResult frame) {
  if (_texture.pixelWidth != 8 || _texture.pixelHeight != 8) {
    throw StateError('this fixture is always 8x8');
  }
  if (_texture.vkFormat != VkFormat.r8g8b8a8UNorm) {
    throw StateError('a Basis file should transcode to plain RGBA8');
  }
  // The top-left quadrant is a flat, near-pure red.
  final topLeft = _texture.levels.first.getUint32(0, Endian.little);
  final red = topLeft & 0xff;
  final green = (topLeft >> 8) & 0xff;
  if (red < 240 || green > 15) {
    throw StateError('the top-left quadrant should transcode close to red');
  }
  if (frame.drawCalls < 1) {
    throw StateError('the block was not drawn');
  }
}
82}