how to use schema.json in gltf2.0

[chen21439]

[featureIdTexture.schema.json.](https://github.com/CesiumGS/glTF/tree/3d-tiles-next/extensions/2.0/Vendor/EXT_mesh_features)

for example in the document,it use shema.json to generate featureId for each vertex,i want to know waht software can do this ,can you give me more information @javagl

[javagl]

As far as I know, there is no software that can assign feature IDs to vertices directly. (I have heard rumors that Blender can assign ~"per-vertex attributes", but this would not be exported to glTF by default). You have to know which vertex should receive which ID, and assign this information to the vertices when you are creating the glTF.

I'm also not aware of any open-source software or library that can (officially) generate glTFs that have this extension. I recently added support for this extension in 3d-tiles-tools, and an example for assigning feature IDs to vertices is shown in the ExtMeshFeaturesDemo.ts. But this is not part of any official API, and it may be changed arbitrarily or even removed at any time. Maybe there will be broader support for this extension in the future.

[chen21439]

@javagl thank you for you reply,i pull the 3d-tiles-tools and run the ExtMeshFeaturesDemo.ts but it throw a error

in method savePixelsInternal

const data = putPixelData(pixels, new Uint8Array(width * height * channels));

the data is empty

[javagl]

From a quick glance, this error seems to come from the ndarray library. What happens when you run this test:

import { savePixels } from "ndarray-pixels";
import NdArray from "ndarray";

async function runTest() {
  const sizeX = 3;
  const sizeY = 3;
  const pixels = NdArray(new Uint8Array(sizeX * sizeY), [sizeX, sizeY]);
  for (let x = 0; x < pixels.shape[0]; x++) {
    for (let y = 0; y < pixels.shape[1]; y++) {
      pixels.set(x, y, x * sizeY + y);
    }
  }
  console.log("pixels ", pixels);
  const image = await savePixels(pixels, "image/png");
  console.log("image ", image);
}

runTest();

[chen21439]

@javagl it shows that

[chen21439]

i think the problem occur in ndarray-pixels-node.cjs putPixelData()

[javagl]

There seems to be a difference between a JavaScript and a TypeScript context. I haven't understood all the details here yet, but opened donmccurdy/ndarray-pixels#156

As a quick fix, you could change the code that fills the pixels, to anticipate that there are 4 channels (and the values are written into channel 3):

  // Create an image with integer values that serve as feature IDs
  const sizeX = 3;
  const sizeY = 3;
  const pixels = NdArray(new Uint8Array(sizeX * sizeY * 4), [sizeX, sizeY, 4]);
  for (let x = 0; x < pixels.shape[0]; x++) {
    for (let y = 0; y < pixels.shape[1]; y++) {
      pixels.set(x, y, 3, x * sizeY + y);
    }
  }

(I haven't tested it thoroughly, but it should solve the issue for now).

But note that the example only generates "some dummy data", only for testing the implementation of the extension. I have also opened CesiumGS/3d-tiles-tools#62 to track the process to create an extended/updated/fixed demo.

[javagl]

I assume that this can be closed for now.

But a small aside: Somone wrote a nice summary of how to add metadata information to models in Blender at https://community.cesium.com/t/gltf2-0-in-ue5-2-metadata-ext-structural-metadata-ext-mesh-features/26873/8 . There may be some manual steps involved, but it will certainly provide a good starting point.