Experimental KTX support

[javagl]

Builds upon #39

Merged with a more recent state, now based on #61

[javagl]

This now includes the state from #61 (so that one should probably be merged first), and a fix to resolve the main issue that prevented this from being merged:

The KtxUtility class offers the functionality that one would like to have in order to convert "any" input image data (PNG or JPG) into a KTX image, and that is

const ktxBuffer = await KtxUtility.convertImageData(pngOrJpgBuffer, options);

Under the hood, this uses the Basis Encoder from https://github.com/BinomialLLC/basis_universal/tree/ad9386a4a1cf2a248f7bbd45f543a7448db15267/webgl/encoder , which is built into a JS+WASM bundle and included here in the ./src/ktx/external directory. As described in the /src/ktx/external/README.md, the latest state of the Basis Encoder caused a runtime error when generating UASTC. This appears to be fixed with updated linker flags (details in the README.md).

I tested this by creating a glTF asset with different encodings of the same texture. Here's an example with the DuckCM.png from the Duck sample model:

DuckCompare.zip

Dragging-and-dropping this into https://gltf.report/ and selecting the 'Textures' tab shows an overview of the textures, their encodings, and their memory requirements:

I also tested this with a 2048x2048 texture (although certain settings cause the encoding to become pretty slow then...), and it seems to work as expected.

[javagl]

The last commit adds a convenience layer around the KTX encoding, so that it is possible to encode all textures in glTF tiles with something like

import { TileContentProcessing } from "./src/tilesetProcessing/TileContentProcessing";
import { TileContentProcessorsTextures } from "./src/tilesetProcessing/TileContentProcessorsTextures";

import { KtxEtc1sOptions } from "./src/ktx/KtxEtc1sOptions";
import { KtxUastcOptions } from "./src/ktx/KtxUastcOptions";

async function runDemo() {
  const tilesetSourceName = "./data/input/tileset.json";
  const tilesetTargetName = "./data/output/tileset.json";
  const overwrite = true;

  // Create a `TileContentProcessor` that encodes textures
  // to KTX, with the given options for ETC1S or UASTC
  const etc1sOptions: KtxEtc1sOptions = {
    compressionLevel: 2,
    qualityLevel: 96,
  };
  const uastcOptions: KtxUastcOptions = {};
  const tileContentProcessor = TileContentProcessorsTextures.encodeToKtx(
    etc1sOptions,
    uastcOptions
  );

  // Process the tileset source, and write it to the tileset target,
  // applying each `TileContentProcessor` to all tile contents
  await TileContentProcessing.process(
    tilesetSourceName,
    tilesetTargetName,
    overwrite,
    tileContentProcessor
  );
}

runDemo();

The functionality for encoding textures may still be added at the command line.