Account for ground albedo

Apps/Sandcastle/gallery/glTF PBR Extensions.html

@@ -135,7 +135,7 @@
  imageBasedLighting.sphericalHarmonicCoefficients = undefined;
  imageBasedLighting.specularEnvironmentMaps = undefined;
  imageBasedLighting.imageBasedLightingFactor = Cesium.Cartesian2.ONE;
- scene.light.intensity = 1.0;
+ scene.light.intensity = 2.0;
  },
  },
  {

packages/engine/Source/Scene/DynamicEnvironmentMapManager.js

@@ -40,6 +40,7 @@ import ConvolveSpecularMapVS from "../Shaders/ConvolveSpecularMapVS.js";
  * @property {number} [brightness=1.0] The brightness of light emitted from the environment. 1.0 uses the unmodified emitted environment color. Less than 1.0 makes the light darker while greater than 1.0 makes it brighter.
  * @property {number} [saturation=1.0] The saturation of the light emitted from the environment. 1.0 uses the unmodified emitted environment color. Less than 1.0 reduces the saturation while greater than 1.0 increases it.
  * @property {Color} [groundColor=DynamicEnvironmentMapManager.AVERAGE_EARTH_GROUND_COLOR] Solid color used to represent the ground.
+ * @property {number} [groundAlbedo=0.31] The percentage of light reflected from the ground. The average earth albedo is 0.31.
  */
 
 /**
@@ -186,6 +187,13 @@ function DynamicEnvironmentMapManager(options) {
  options.groundColor,
  DynamicEnvironmentMapManager.AVERAGE_EARTH_GROUND_COLOR,
  );
+
+ /**
+ * The percentage of light reflected from the ground. The average earth albedo is 0.31.
+ * @type {number}
+ * @default 0.31
+ */
+ this.groundAlbedo = defaultValue(options.groundAlbedo, 0.31);
 }
 
 Object.defineProperties(DynamicEnvironmentMapManager.prototype, {
@@ -480,7 +488,8 @@ function updateRadianceMap(manager, frameState) {
  u_faceDirection: () => CubeMap.getDirection(face, scratchCartesian),
  u_positionWC: () => position,
  u_brightnessSaturationGammaIntensity: () => adjustments,
- u_groundColor: () => manager.groundColor,
+ u_groundColor: () =>
+ manager.groundColor.withAlpha(manager.groundAlbedo),
  },
  persists: true,
  owner: manager,
@@ -827,11 +836,11 @@ DynamicEnvironmentMapManager.prototype.destroy = function () {
 };
 
 /**
- * Average hue of ground color on earth, a warm gray.
+ * Average hue of ground color on earth, a warm green-gray.
  * @type {Color}
  */
 DynamicEnvironmentMapManager.AVERAGE_EARTH_GROUND_COLOR = Object.freeze(
- Color.fromCssColorString("#423c35"),
+ Color.fromCssColorString("#717145"),
 );
 
 export default DynamicEnvironmentMapManager;

packages/engine/Source/Shaders/ComputeRadianceMapFS.glsl

@@ -6,7 +6,7 @@ uniform vec3 u_faceDirection; // Current cubemap face
 uniform vec3 u_positionWC;
 uniform mat4 u_enuToFixedFrame;
 uniform vec4 u_brightnessSaturationGammaIntensity;
-uniform vec4 u_groundColor;
+uniform vec4 u_groundColor; // alpha component represent albedo
 
 vec4 getCubeMapDirection(vec2 uv, vec3 faceDir) {
  vec2 scaledUV = uv * 2.0 - 1.0;
@@ -69,19 +69,22 @@ void main() {
  vec4 sceneSkyBoxColor = czm_textureCube(czm_environmentMap, lookupDirection);
  vec3 skyBackgroundColor = mix(czm_backgroundColor.rgb, sceneSkyBoxColor.rgb, sceneSkyBoxColor.a);
 
- // Interpolate the ground color based on distance and sun exposure
+ // Apply intensity to sky light
+ float intensity = u_brightnessSaturationGammaIntensity.w;
+ vec4 adjustedSkyColor = skyColor;
+ adjustedSkyColor.rgb = skyColor.rgb * intensity;
+
+ // Compute ground color based on amount of reflected light
+ vec3 groundColor = u_groundColor.rgb * u_groundColor.a * adjustedSkyColor.rgb;
+
+ // Interpolate the ground color based on angle of sun exposure and distance from the ground
  vec3 up = normalize(u_positionWC);
- float occlusion = max(dot(lightDirectionWC, up), 0.15); // Ensure a low-level of ambiant light reflected from the ground.
- vec3 groundColor = mix(vec3(0.0), u_groundColor.rgb, occlusion * u_groundColor.a * (1.0 - d / radius));
+ float occlusion = max(dot(lightDirectionWC, up), 0.15);
+ groundColor = mix(vec3(0.0), u_groundColor.rgb, occlusion * (1.0 - d / radius));
 
  // Only show the stars when not obscured by the ellipsoid
  vec3 backgroundColor = czm_branchFreeTernary(czm_isEmpty(intersection), skyBackgroundColor, groundColor);
 
- // Apply intensity to sky only
- float intensity = u_brightnessSaturationGammaIntensity.w;
- vec4 adjustedSkyColor = skyColor;
- adjustedSkyColor.rgb = skyColor.rgb * intensity;
-
  vec4 color = vec4(mix(backgroundColor, adjustedSkyColor.rgb, adjustedSkyColor.a), 1.0);
 
  float brightness = u_brightnessSaturationGammaIntensity.x;