Added STK atmosphere improvements

CHANGES.md

@@ -8,6 +8,7 @@ Change Log
 * Fixed issue where the `Model` glTF cache loses reference to the model's buffer data. [#5720](https://github.com/AnalyticalGraphicsInc/cesium/issues/5720)
 * Fixed some issues with `disableDepthTestDistance` [#5501](https://github.com/AnalyticalGraphicsInc/cesium/issues/5501) [#5331](https://github.com/AnalyticalGraphicsInc/cesium/issues/5331) [#5621](https://github.com/AnalyticalGraphicsInc/cesium/issues/5621)
 * Added several new Bing Maps styles: `CANVAS_DARK`, `CANVAS_LIGHT`, and `CANVAS_GRAY`.
+* Added small improvements to the atmosphere.
 
 ### 1.36 - 2017-08-01
 

Source/Shaders/SkyAtmosphereFS.glsl

@@ -37,6 +37,8 @@
 uniform vec3 u_hsbShift; // Hue, saturation, brightness
 #endif
 
+uniform vec4 u_cameraAndRadiiAndDynamicAtmosphereColor; // Camera height, outer radius, inner radius, dynamic atmosphere color flag
+
 const float g = -0.95;
 const float g2 = g * g;
 
@@ -73,5 +75,12 @@ void main (void)
     l = min(l, czm_luminance(rgb));
 #endif
 
-    gl_FragColor = vec4(rgb, min(smoothstep(0.0, 0.1, l), 1.0) * smoothstep(0.0, 1.0, czm_morphTime));
+    // Alter alpha based on how close the viewer is to the ground (1.0 = on ground, 0.0 = at edge of atmosphere)
+    float atmosphereAlpha = clamp((u_cameraAndRadiiAndDynamicAtmosphereColor.y - length(czm_viewerPositionWC)) / (u_cameraAndRadiiAndDynamicAtmosphereColor.y - u_cameraAndRadiiAndDynamicAtmosphereColor.z), 0.0, 1.0);
+
+    // Alter alpha based on time of day (0.0 = night , 1.0 = day)
+    float nightAlpha = (u_cameraAndRadiiAndDynamicAtmosphereColor.w > 0.0) ? clamp(dot(normalize(czm_viewerPositionWC), normalize(czm_sunPositionWC)), 0.0, 1.0) : 1.0;
+    atmosphereAlpha *= pow(nightAlpha, 0.5);
+
+    gl_FragColor = vec4(rgb, mix(rgb.b, 1.0, atmosphereAlpha) * smoothstep(0.0, 1.0, czm_morphTime));
 }

Source/Shaders/SkyAtmosphereVS.glsl

@@ -2,11 +2,11 @@
  * @license
  * Copyright (c) 2000-2005, Sean O'Neil (s_p_oneil@hotmail.com)
  * All rights reserved.
- * 
+ *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
- * 
+ *
  * * Redistributions of source code must retain the above copyright notice,
  *   this list of conditions and the following disclaimer.
  * * Redistributions in binary form must reproduce the above copyright notice,
@@ -15,7 +15,7 @@
  * * Neither the name of the project nor the names of its contributors may be
  *   used to endorse or promote products derived from this software without
  *   specific prior written permission.
- * 
+ *
  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
@@ -29,10 +29,10 @@
  *
  * Modifications made by Analytical Graphics, Inc.
  */
- 
+
  // Code:  http://sponeil.net/
  // GPU Gems 2 Article:  http://http.developer.nvidia.com/GPUGems2/gpugems2_chapter16.html
-  
+
 attribute vec4 position;
 
 uniform vec4 u_cameraAndRadiiAndDynamicAtmosphereColor; // Camera height, outer radius, inner radius, dynamic atmosphere color flag
@@ -49,7 +49,7 @@ const vec3 InvWavelength = vec3(
     9.473284437923038, // Green = 1.0 / Math.pow(0.570, 4.0)
     19.643802610477206); // Blue = 1.0 / Math.pow(0.475, 4.0)
 const float rayleighScaleDepth = 0.25;
-          
+
 const int nSamples = 2;
 const float fSamples = 2.0;