Darken fog when terrain lighting is enabled.

[bagnell]

Darkens the fog when viewer.scene.globe.enableLighting = true. Here is a Sandcastle example for testing:

var viewer = new Cesium.Viewer('cesiumContainer');

viewer.terrainProvider = new Cesium.CesiumTerrainProvider({
    url : 'https://assets.agi.com/stk-terrain/v1/tilesets/world/tiles',
    requestVertexNormals : true
});

viewer.scene.globe.enableLighting = true;

var camera = viewer.scene.camera;
camera.position = new Cesium.Cartesian3(305111.15252842277, 5635080.182335396, 2980739.393793938);
camera.direction = new Cesium.Cartesian3(-0.8922165975346716, 0.21339304915721466, -0.39801124312642266);
camera.up = new Cesium.Cartesian3(0.012013291290700188, 0.8922235826513757, 0.4514341141219929);
camera.right = Cesium.Cartesian3.cross(camera.direction, camera.up, new Cesium.Cartesian3());
viewer.clock.currentTime = new Cesium.JulianDate(2458052, 45720.28193048129);

CC @emackey

[cesium-concierge]

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[bagnell]

[pjcozzi]

Here and where ever else just

fogColor *= darken;

?

[emackey]

This is an awesome change, much needed! I agree with Cozzi's optimization and added an additional suggestion below. I use enableLighting in a number of apps that will see automatic benefit from this.

[emackey]

0.1 is a magic number that may not be ideal for all cases. Is it possible to add a user configuration setting for this? It won't need to change at runtime, I imagine any app that wanted to tweak it would just set their preferred value prior to initializing a viewer. But I think app authors will want control over this minimum terrain brightness value.

[bagnell]

@pjcozzi @emackey This is ready for another look.

[pjcozzi]

Thanks @bagnell! @emackey please merge when ready.

[emackey]

Awesome. Thanks for viewer.scene.fog.minimumBrightness.

/ping @abwood