Fix billboard and label clamping

[mramato]

Turns out that billboard and label clamping were fundamentally broken because the QuadtreePrimitive was processing the tile queue in the wrong order. It was always pulling new tiles from the back of the array rather than the front, which meant that data would get processed in the wrong order causing old tiles to take precedence over newer tiles.

Additionally, there was a bad if block in Label.js which caused the initial position of the individual label billboards to not be properly set when clamping was on, instead we should always set the positions before calling _updateClamping (if needed).

Fixes #4396 and #4062

I already talked to @bagnell about this and he agreed it was a straight up bug. I would love to add unit tests for these, but I'm not sure what the best strategy would be.

There are still several other clamping related issues that I'm looking into; but I wanted to keep these PRs small for easier review.

[hpinkos]

Am i doing something wrong? #4026 doesn't seem to be fixed. The billboards look all over the place to me.

var viewer = new Cesium.Viewer('cesiumContainer', {
    baseLayerPicker: false,
    terrainProvider: new Cesium.CesiumTerrainProvider({
        url : 'https://assets.agi.com/stk-terrain/world',
        requestWaterMask : true,
        requestVertexNormals : true
    })
});
var options = {
    camera : viewer.scene.camera,
    canvas : viewer.scene.canvas,
    clampToGround: true
};
viewer.dataSources.add(Cesium.KmlDataSource.load('../../SampleData/kml/facilities/facilities.kml', options));

[hpinkos]

[mramato]

Works for me, are you waiting long enough, it can be slow?

[denverpierce]

I'm not seeing the floaters anymore, but clamping perf appears a lot worse on this, because billboard and labels are dropping below the terrain before jumping back up.

I tried to get a gif of it, but it ended up taking so long to represent it, the file ends up larger than 10mb.

[mramato]

I'm not seeing the floaters anymore, but clamping perf appears a lot worse on this, because billboard and labels are dropping below the terrain before jumping back up.

I tried to get a gif of it, but it ended up taking so long to represent it, the file ends up larger than 10mb.

Yes, performance appears a lot worse because it is now more correct and doing thing in the proper order. The next step is to fix the actual performance issues but that will happen in future PRs.

There's also still some clamp related bugs that need to be addressed independently, but this is definitely an important incremental improvements.

[hpinkos]

@denverpierce what seems to be happening for me is that clamping works for a little bit, then as i zoom in and out and click around to target different billboards it seems to stop working after a little bit.

@pjcozzi can you review and merge this?

[mramato]

I have another change that I'm going to PR into this branch because it may be a bit controversial.

[mramato]

I opened #4497, can people please try that out and let me know what you think.

[mramato]

Since #4497 has been retargeted, this is ready unless there are other comments.

[pjcozzi]

Will look at this shortly.

[pjcozzi]

For #4062, the labels didn't clamp to terrain for me:

[mramato]

Did you turn terrain on after you loaded the KML? If so they won't clamp because that's fixed with #4497

[mramato]

Actually, I think changing terrain is yet another unrelated clamping bug, I'm looking at that separately now.

[denverpierce]

Works for me, but when you switch terrain, depth testing comes on, and due to #4090 KML billboards are centered, so they occlude a bit.

Facilities isn't a great example, but here's how it looks when you turn on terrain with clamping in this branch:

[mramato]

Works for me, but when you switch terrain, depth testing comes on, and due to #4090 KML billboards are centered, so they occlude a bit.

Thanks for testing @denverpierce. I actually think this is a bug in the facilities.kml file itself, but I have to check. Also, did you turn terrain on after the fact? I think there is a separate bug where terrain needs to be turned on before the data is added but I'm not sure.

[bagnell]

This fixes #4396 and the misplaced glyphs of a label, but it does not fix #4062 completely.