[BUG] Transparent individual pointcloud classes don't get rendered as transparent

[airnez]

Context

I am using classified pointclouds provided as 3D Tiles.
I am setting a custom classificationScheme to choose color and opacity for each individual pointcloud class.
Setting colors works fine. Reducing opacity will however fade the point color to white instead of making it transparent.
On the screenshot bellow the buildings are excpected to look half-transparent red but appear pink and opaque instead.

Steps to Reproduce

1. Render a classified point cloud 3D Tile source (https://raw.githubusercontent.com/iTowns/iTowns2-sample-data/master/pointclouds/pnts-sete-2021-0756_6256/tileset.json)
2. Set a custom classification scheme with a transparent class (here buildings are set red and half-transparent and the rest is black) :

layer.classification = {
                    6: { visible: true, color: new THREE.Color(1, 0, 0), opacity: 0.5 },
                    DEFAULT: { visible: true, color: new THREE.Color(0, 0, 0), opacity: 1 }
}

Expected Behavior

The classified points should be rendered as transparent.

Actual Behavior

The classified point are getting whiter.

Possible Cause/Fix/Solution

It seems that the point material transparent property is not set correctly. Thus it renders the color alpha as color intensity instead of transparency. This happens because the layer opacity is set to 1. Even if we try to set the whole layer material transparent, the transparent property getter overwrites the value depending on the opacity. See here :

itowns/src/Layer/ReferencingLayerProperties.js

Lines 48 to 56 in 48fb9df

	Object.defineProperty(material, 'transparent', {
	get: () => {
	if (transparent != material.layer.opacity < 1.0) {
	material.needsUpdate = true;
	transparent = material.layer.opacity < 1.0;
	}
	return transparent;
	},
	});

[ftoromanoff]

Linked with your issue, I noticed a similar bug on PointCloudLayer (entwine and Potree).
I started a PR #2327 to fix that issue, but currently I only look up for PointCloud and not yet other 3D Layer type (as 3D tiles you are refering to here)

[ftoromanoff]

The last commits of the PR #2327 should fix it. @airnez You can try to see if it is what you wanted ?
It might get reworked, but it might be good to know if the issue you pointed out is resolved like that.

[airnez]

I tested your fix, and I couldn't make it work for 3dTiles. I suspect that the problem is linked to the fact that the 3dTiles pointsMaterial is instanciated here :

itowns/src/Provider/3dTilesProvider.js

Lines 34 to 50 in 14891fd

	function pntsParse(data, layer) {
	return PntsParser.parse(data, layer.registeredExtensions).then((result) => {
	const material = layer.material ?
	layer.material.clone() :
	new PointsMaterial({
	size: 0.05,
	mode: layer.pntsMode,
	shape: layer.pntsShape,
	classification: layer.classification,
	sizeMode: layer.pntsSizeMode,
	minAttenuatedSize: layer.pntsMinAttenuatedSize,
	maxAttenuatedSize: layer.pntsMaxAttenuatedSize,
	});
	// refer material properties in the layer so when layers opacity and visibility is updated, the material is
	// automatically updated
	ReferLayerProperties(material, layer);

It seems that something like what you implemented here is needed : https://github.com/ftoromanoff/itowns/blob/41fbaa3780245939b50cbc8b19cc79287de8aa2f/src/Layer/PointCloudLayer.js#L197

[ftoromanoff]

Should be fixed now.
I indeed did a last little change that i forgot to apply on 3dTilesLayer...

[airnez]

Tested, it seems fixed ! Thank you @ftoromanoff