WebGLRenderer: Enable rendering without index and position attribute

[Mugen87]

Fixes #10751

We only use dataCount in order to determine drawEnd if an index or a position attribute is present. Otherwise, it will use Infinity inside the Math.min statement.

Like mentioned in the issue, it's necessary to specify drawRange (or group) if a geometry consists only of custom attributes.

[WestLangley]

If you are not going to use dataCount, there is no need to compute it in the previous lines.

Is this PR equivalent to just initializing dataCount to Infinity?

[Mugen87]

If we initialize dataCount to Infinity, then we might have problems with such setups: #8395 (comment)

If you are not going to use dataCount, there is no need to compute it in the previous lines.

How would you write it differently? If index is null and position is undefined, the value of dataCount ist still 0.

[WestLangley]

How would you write it differently?

By initializing dataCount to infinity and removing the remainder of your changes. I think it is the same.

I'm not sure if there is a downside to supporting this feature, however....

[Mugen87]

By initializing dataCount to infinity and removing the remainder of your changes. I think it is the same.

Yes, you're right. I've checked #8395 again. I was just concerned about empty Geometry objects. But when they are converted to BufferGeometry, they have at least a position attribute.

[mrdoob]

Thanks!