Extend Sytling to allow check for existing of a property

[SunBlack]

Currenlty you have to make sure a property exists if you use it in Cesium3DTileStyle. But if you have a generic UI sometimes you don't know if a Tileset as has property, because its depend on conent of each tile.

So following code can cause a crash if MYPORPERTY does not exists:

    var tileset = new Cesium3DTileset({url : 'data'});
    tileset.style = new Cesium3DTileStyle({
        "color" : {
            "conditions" : [
                ["(${MYPORPERTY} === 0)", "rgb(196, 196, 196)"],
                ["(${MYPORPERTY} === 1)", "rgb(128, 128, 128)"],
                ["true", "rgb(255, 255, 255)"],
            ]
        }
    });

So it would be nice if you could write something like this:

    var tileset = new Cesium3DTileset({url : 'data'});
    tileset.style = new Cesium3DTileStyle({
        "color" : {
            "conditions" : [
                ["(defined(${MYPORPERTY}) && ${MYPORPERTY} === 0)", "rgb(196, 196, 196)"],
                ["(defined(${MYPORPERTY}) && ${MYPORPERTY} === 1)", "rgb(128, 128, 128)"],
                ["true", "rgb(255, 255, 255)"],
            ]
        }
    });

In case this is to complex another suggestion would be to extent it to

var tileset = new Cesium3DTileset({url : 'data'});
tileset.style = new Cesium3DTileStyle({
	"color" : [
		{
			"required_properties" : [
				"MYPORPERTY", "MYPORPERTY2", 
			],
			"conditions" : [
				["(${MYPORPERTY} === 0 && ${MYPORPERTY2} === 0)", "rgb(196, 196, 196)"],
				["(${MYPORPERTY} === 0 && ${MYPORPERTY2} === 1)", "rgb(164, 164, 164)"],
				["(${MYPORPERTY} === 1 && ${MYPORPERTY2} === 0)", "rgb(128, 128, 128)"],
				["(${MYPORPERTY} === 1 && ${MYPORPERTY2} === 1)", "rgb(92, 92, 92)"],
				["true", "rgb(255, 255, 255)"],
			],
		},
		{
			"required_properties" : [
				"MYPORPERTY"
			],
			"conditions" : [
				["(${MYPORPERTY} === 0)", "rgb(196, 196, 196)"],
				["(${MYPORPERTY} === 1)", "rgb(128, 128, 128)"],
				["true", "rgb(255, 255, 255)"],
			],
		},
		{
			"rgb(255, 255, 255)"
		}
	}
});

[lilleyse]

Yes this is a good point for the point cloud styling engine, which won't work if a style references a non-existent property. We should be smarter about detecting non-existent properties ahead of time.

Adding defined may not be needed since {MYPORPERTY} !== undefined is valid. It might be a good idea though.

[pjcozzi]

CC #3241

Also added link from CesiumGS/3d-tiles#140 where it is suggested that undefined may be able to evaluate to 0 or false with the GLSL backend.

[VolodKu]

So what is the solution for this case?
It shows error below
Error generating style shader: undefined is not supported.

[VolodKu]

Before applying how can I check with undefined?
If you can provide, it's much appreciated.
Thanks