Apply styles to photogrammetry

[lilleyse]

Fixes #7149

Styles now work for tilesets that don't have features. All property expressions (e.g. ${Height}) evaluate to undefined.

@OmarShehata can you review?

tileset.style = new Cesium.Cesium3DTileStyle({
    color : 'rgba(255, 0, 0, 0.5)'
});

[cesium-concierge]

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[pjcozzi]

@lilleyse does this require a spec update - either normative or implementation note?

[lilleyse]

After reading the styling page, yes it does require normative update. I opened a spec PR here: CesiumGS/3d-tiles#352.

[OmarShehata]

This is awesome @lilleyse ! I can run my original transparency demo from the forum thread now. All tests are passing, and works in Chrome, Edge and IE11.

The only thing I feel uneasy about is:

function evaluateTilesetTime(feature) {
    if (!defined(feature)) {
        return 0.0;
    }
    return feature.content.tileset.timeSinceLoad;
}

Since that means photogrammetry wouldn't be able to use time-based styles, and it would be kind of opaque to the user why this doesn't work. This built in time variable is only documented in the spec, and it would be strange to add to add this CesiumJS specific implementation issue there.

I guess getting that to work would require passing in the original tileset to the evaluate function? Is that a difficult refactor? It might be worth at least opening up an issue for.

[lilleyse]

We could add more info to this issue #5550.

Basically tiles3d_tileset_time only actually works for point clouds right now.

[OmarShehata]

Oh! Yeah I think in that case, just update that issue saying that it also won't work when there are no features, and I think this is good to merge.

I can bump the forum thread once it's merged.

[lilleyse]

I updated #5550.

[OmarShehata]

You have to merge this yourself by the way @lilleyse .

[mramato]

@ggetz please do a final review and merge. Thanks.

[ggetz]

Why is this an exception? It looks like we determine the behavior in the previous test for what do when printing an undefined property.

[lilleyse]

Oh just an exception in reference to the name of the test "evaluates variable to undefined if feature is undefined"

[ggetz]

Looks good other than that one comment.