billboard being incorrectly culled

1. Run the below code.
2. Gecoder to Matagorda Island and double click on the only placemark in the upper right (also Matagorda Island)
3. Rotate the camera up and down and the billboard will blink on and off.

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));

[emackey]

So perhaps every Primitive with depth testing disabled should end up in the front most Frustum.

My current thinking on this topic is that all 2D primitives end up in their own render pass, with some kind of single-3D-point depth test to determine visibility status of the primitive. The primitive would exist outside of any 3D frustums and would not have per-fragment depth testing. See thread: https://github.com/AnalyticalGraphicsInc/cesium/issues/2694#issuecomment-338168783

[emackey]

In the above screenshot, I suspect all of those yellow points are actually sticking into the globe. Cesium does a good job keeping things like billboards from “sticking into the globe”, but the globe-depth tricks break down across frustum boundaries. So for the clipped yellow dots above, the yellow fragments are being rendered into a rear frustum, and the globe imagery is being rendered into a closer frustum, and there’s a depth buffer clear in between. There’s no easy way to allow the points to show through the globe at the boundary, because they are legitimately occluded.