Three drops indices when converting from a Geometry > BufferGeometry

Description of the problem

Every face in a Geometry has a materialIndex. When Three converts from a Geometry to a BufferGeometry…

var bufferGeometry = THREE.BufferGeometry.new().fromGeometry(geometry);

…there’s an intermediary step where a DirectGeometry is used…

fromGeometry: function ( geometry ) {
    geometry.__directGeometry = new DirectGeometry().fromGeometry( geometry );

Note that a DirectGeometry defines an indices array, then does nothing with it.

So it’s not surprising when BufferGeometry checks the intermediary directGeometry.indices.length, it won’t ever be populated.

When the BufferGeometry comes out the other end, it has no indices. bufferGeometry.getIndex() is null.

It looks like DirectGeometry’s ability to handle indices was removed two years ago.

Here’s a CodePen demonstrating the problem. Check the logs. The merged geometry should have indices returned, but it doesn’t. https://codepen.io/andrewray/pen/gRyrzR?editors=0010

Three.js version

• Dev
• r85

Browser

• All of them

OS

• All of them

[WestLangley]

@Bryce-Summers If you mean the option to return indexed BufferGeometry, no, because in most cases it is not reasonable, and it adds a lot of additional logic to the loader.

BTW, would returning non-indexed BufferGeoemtry and simply adding an attribute originalIndex solve your problem?

[mrdoob]

Every face in a Geometry has a materialIndex. When Three converts from a Geometry to a BufferGeometry…

materialIndex and indices are different things though. materialIndex refers to multi-materials. indices refer to attribute indices.

Note that a DirectGeometry defines an indices array, then does nothing with it.

Good catch!

It looks like DirectGeometry’s ability to handle indices was removed two years ago.

It was also added some weeks before that. Basically, I was trying to keep indices somehow but it was not really possible so I removed it.