Use clamped material.emissiveIntensity at GLTF export

[SBRK]

Related issue: Fixed #22000

Description

With the recent change that exported emissive without multiplying by emissiveIntensity, materials that had an emissiveIntensity between 0 and 1 would come out too bright on exported gltf.
Clamping the emissiveIntensity between 0 and 1 before multiplying by it ensures the output GLTF complies with specs and emissiveFactor r g b components are between 0 and 1

[WestLangley]

That is not what I tried to suggest :-) . See #22000 (comment).

First scale the color by intensity.

If any RGB component exceeds 1, scale the color by ( 1 / max-component ) and throw a warning.

I think that is the best temporary workaround until the glTF specification is updated.

[SBRK]

@WestLangley but if we do that, then we might end up with a color that is much different than the original, right ? (in most cases, just white)

[SBRK]

Ok scrap my previous comment, I see what you mean. If one component exceeds 1, then scale ALL components by (1 / max component). It will indeed keep the right hue and scale closer to the intended emissiveIntensity than if we just clamp it before scaling

[WestLangley]

Right. Something like this:

const emissive = material.emissive.clone().multiplyScalar( material.emissiveIntensity );

const maxEmissiveComponent = Math.max( emissive.r, emissive.g, emissive.b );

if ( maxEmissiveComponent > 1 ) {

	emissive.multiplyScalar( 1 / maxEmissiveComponent );

	console.warn( 'THREE.GLTFExporter: Some emissive components exceed 1; emissive has been limited' );

}

if ( maxEmissiveComponent > 0 ) {

	materialDef.emissiveFactor = emissive.toArray();

}

[mrdoob]

@SBRK I think @WestLangley's suggestion is more readable 👍

[SBRK]

You're right. I implemented his suggestion

[mrdoob]

Thanks!