[Bug] GLTF: Handle URI shader

[Niklas Kraßnig]

Hi,

this tileset from the city of Vienna contains shaders that are base64 Uri encoded. When you try to execute the code below it crashes:

Sadly you don't see the stack trace that caused the error, so I tried to debug it. In @loaders.gl\gltf\src\lib\extensions\deprecated\KHR_techniques_webgl.ts in the function resolveTechniques() (link) there is a TODO: handle URI shader which is not yet implemented.

Here is a quick fix that happens to work on this specific scenario:

shaders.forEach(shader => {
  if (Number.isFinite(shader.bufferView)) {
    shader.code = textDecoder.decode(gltfScenegraph.getTypedArrayForBufferView(shader.bufferView));
  } else if (typeof shader.uri === 'string' && shader.uri.startsWith('data:application/octet-stream;base64,')) {
    const base64 = shader.uri.substring('data:application/octet-stream;base64,'.length);
    shader.code = atob(base64);
  } else {
    throw new Error('KHR_techniques_webgl: no shader code');
  }
});

This solution has some limitations as outlined in the MDN Base64.

Here is a minimal script to reproduce the error:

import { Tiles3DLoader } from "@loaders.gl/3d-tiles";
import { load } from "@loaders.gl/core";
import { Tileset3D } from "@loaders.gl/tiles";
import { WebMercatorViewport } from "@deck.gl/core/typed";

main();
async function main() {
	// tilset of vienna
	const tilesetJson = await load('https://www.wien.gv.at/stadtplan3d/datasource-data/5fd17961-5606-47c0-a955-e56deb6bf388/tileset.json', Tiles3DLoader);
	const tileset3d = new Tileset3D(tilesetJson, {
		onTileLoad: tile => {
			console.info('tile loaded: ', tile);
		},
		onTileError: error => {
			console.warn('tile erred: ', error);
		}
	});

	// center of the city, Stephansdom
	tileset3d.selectTiles(new WebMercatorViewport({
		width: 1000,
		height: 1000,
		latitude: 48.20877518529593,
		longitude: 16.372505487554207,
		zoom: 18
	}));
}

Note: For this script to work you need to first disable CORS.

[Ib Green]

Yes, we have decided to not support the KHR_techniques_webgl WebGL extension (that extension was never ratified and supporting it has many issues).

I realize that there is some vestigial code still in there, ideally it should be removed and a better error message produced, and docs could be clearer.