Missing notification of changed 3d Tile Style

[SunBlack]

Example:

var tileset = new Cesium3DTileset({url : 'data'});
tileset.style = new Cesium3DTileStyle({
	color: 'vec4(1.0, 0.0, 0.0, 1.0)'
});
setTimeout(function() {
	tileset.style.color = new Expression('vec4(0.0, 1.0, 0.0, 1.0)');
}, 10000);

Expected: Color of displayed changes from red to green.
Got: Only new loaded data are displayed green.

Current workaround:

setTimeout(function() {
	tileset.style = new Cesium3DTileStyle({
		color: 'vec4(0.0, 1.0, 0.0, 1.0)'
	});
}, 10000);

How this can be fixed: In case a value is changed there should be triggered an event to make style dirty. On this way all shader will be recompiled. In some cases, e.g. pointSize it is not necessary to recompile shader, because the size of points are stored in a uniform (I have no idea when the uniform currently will be ever adjusted).

[lilleyse]

Another workaround is to call tileset.makeStyleDirty().

[pjcozzi]

Calling tileset.makeStyleDirty() is not a workaround; it is the right way to do this.

Otherwise, styling would be too slow since each feature would have to evaluate the style each frame.

[pjcozzi]

@lilleyse consider adding this to a Sandcastle example in #5308. I had it at one point but looks like it was removed.

[SunBlack]

I was thinking about a signal which Cesium3DTileStyle send to all Cesium3DTileset which are using this style. On this way Cesium3DTileset don't need to check if a style has been changed.

[pjcozzi]

@SunBlack feel free to explore and open a PR for discussion. It's been awhile since I designed this but I might have also ruled that out for complexity or performance, but it could be worth reevaluating.