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import defined from "../Core/defined.js";
import DeveloperError from "../Core/DeveloperError.js";
import CesiumMath from "../Core/Math.js";
import SceneMode from "./SceneMode.js";
/**
* Blends the atmosphere to geometry far from the camera for horizon views. Allows for additional
* performance improvements by rendering less geometry and dispatching less terrain requests.
*
* @demo {@link https://sandcastle.cesium.com/index.html?src=Fog.html|Cesium Sandcastle Fog Demo}
*
* @alias Fog
* @constructor
*/
function Fog() {
/**
* <code>true</code> if fog is enabled, <code>false</code> otherwise.
* @type {boolean}
* @default true
* @example
* // Disable fog in the scene
* viewer.scene.fog.enabled = false;
*/
this.enabled = true;
/**
* <code>true</code> if fog is renderable in shaders, <code>false</code> otherwise.
* This allows to benefits from optimized tile loading strategy based on fog density without the actual visual rendering.
* @type {boolean}
* @default true
* @example
* // Use fog culling but don't render it
* viewer.scene.fog.enabled = true;
* viewer.scene.fog.renderable = false;
*/
this.renderable = true;
/**
* A scalar that determines the density of the fog. Terrain that is in full fog are culled.
* The density of the fog increases as this number approaches 1.0 and becomes less dense as it approaches zero.
* The more dense the fog is, the more aggressively the terrain is culled. For example, if the camera is a height of
* 1000.0m above the ellipsoid, increasing the value to 3.0e-3 will cause many tiles close to the viewer be culled.
* Decreasing the value will push the fog further from the viewer, but decrease performance as more of the terrain is rendered.
* @type {number}
* @default 0.0006
* @example
* // Double the default fog density
* viewer.scene.fog.density = 0.0012;
*/
this.density = 0.0006;
/**
* A scalar used in the function to adjust density based on the height of the camera above the terrain.
* @type {number}
* @default 0.001
*/
this.heightScalar = 0.001;
this._heightFalloff = 0.59;
/**
* The maximum height fog is applied. If the camera is above this height fog will be disabled.
* @type {number}
* @default 800000.0
*/
this.maxHeight = 800000.0;
/**
* A scalar that impacts the visual density of fog. This value does not impact the culling of terrain.
* Use in combination with the {@link Fog.density} to make fog appear more or less dense.
* @type {number}
* @default 0.15
* @experimental The value of this scalar may not be final and is subject to change.
* @example
* // Increase fog appearance effect
* viewer.scene.fog.visualDensityScalar = 0.6;
*/
this.visualDensityScalar = 0.15;
/**
* A factor used to increase the screen space error of terrain tiles when they are partially in fog. The effect is to reduce
* the number of terrain tiles requested for rendering. If set to zero, the feature will be disabled. If the value is increased
* for mountainous regions, less tiles will need to be requested, but the terrain meshes near the horizon may be a noticeably
* lower resolution. If the value is increased in a relatively flat area, there will be little noticeable change on the horizon.
* @type {number}
* @default 2.0
*/
this.screenSpaceErrorFactor = 2.0;
/**
* The minimum brightness of the fog color from lighting. A value of 0.0 can cause the fog to be completely black. A value of 1.0 will not affect
* the brightness at all.
* @type {number}
* @default 0.03
*/
this.minimumBrightness = 0.03;
}
Object.defineProperties(Fog.prototype, {
/**
* Exponent factor used in the function to adjust how density changes based on the height of the camera above the ellipsoid. Smaller values produce a more gradual transition as camera height increases.
* Value must be greater than 0.
* @memberof Fog.prototype
* @type {number}
* @default 0.59
*/
heightFalloff: {
get: function () {
return this._heightFalloff;
},
set: function (value) {
//>>includeStart('debug', pragmas.debug);
if (defined(value) && value < 0) {
throw new DeveloperError("value must be positive.");
}
//>>includeEnd('debug');
this._heightFalloff = value;
},
},
});
const scratchPositionNormal = new Cartesian3();
/**
* @param {FrameState} frameState
* @private
*/
Fog.prototype.update = function (frameState) {
const enabled = (frameState.fog.enabled = this.enabled);
if (!enabled) {
return;
}
frameState.fog.renderable = this.renderable;
const camera = frameState.camera;
const positionCartographic = camera.positionCartographic;
// Turn off fog in space.
if (
!defined(positionCartographic) ||
positionCartographic.height > this.maxHeight ||
frameState.mode !== SceneMode.SCENE3D
) {
frameState.fog.enabled = false;
frameState.fog.density = 0;
return;
}
const height = positionCartographic.height;
let density =
this.density *
this.heightScalar *
Math.pow(
Math.max(height / this.maxHeight, CesiumMath.EPSILON4),
-Math.max(this._heightFalloff, 0.0),
);
// Fade fog in as the camera tilts toward the horizon.
const positionNormal = Cartesian3.normalize(
camera.positionWC,
scratchPositionNormal,
);
const dot = Math.abs(Cartesian3.dot(camera.directionWC, positionNormal));
density *= 1.0 - dot;
frameState.fog.density = density;
frameState.fog.visualDensityScalar = this.visualDensityScalar;
frameState.fog.sse = this.screenSpaceErrorFactor;
frameState.fog.minimumBrightness = this.minimumBrightness;
};
export default Fog;
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