Merge pull request #3965 from likangning93/vanishingAtmosphere

Vanishing atmosphere when looking up #3347

CHANGES.md

@@ -25,6 +25,7 @@ Change Log
 * Fixed a bug that would cause a crash is the camera was on the IDL in 2D. [#3951](https://github.com/AnalyticalGraphicsInc/cesium/issues/3951)
 * Added `Scene.nearToFarDistance2D` that determines the size of each frustum of the multifrustum in 2D.
 * Added support for rendering models in 2D and Columbus view.
+* Fixed a bug that was causing the atmosphere to disappear when only atmosphere is visible. [#3347](https://github.com/AnalyticalGraphicsInc/cesium/issues/3347) 
 
 ### 1.21 - 2016-05-02
 

Source/Scene/Scene.js

@@ -571,6 +571,7 @@ define([
 
             isSunVisible : false,
             isMoonVisible : false,
+            isReadyForAtmosphere : false,
             isSkyAtmosphereVisible : false,
 
             clearGlobeDepth : false,
@@ -1238,7 +1239,7 @@ define([
 
         // Determine visibility of celestial and terrestrial environment effects.
         var environmentState = scene._environmentState;
-        environmentState.isSkyAtmosphereVisible = defined(environmentState.skyAtmosphereCommand) && defined(scene.globe) && scene.globe._surface._tilesToRender.length > 0;
+        environmentState.isSkyAtmosphereVisible = defined(environmentState.skyAtmosphereCommand) && environmentState.isReadyForAtmosphere;
         environmentState.isSunVisible = isVisible(environmentState.sunDrawCommand, cullingVolume, occluder);
         environmentState.isMoonVisible = isVisible(environmentState.moonCommand, cullingVolume, occluder);
 
@@ -1919,6 +1920,7 @@ define([
         var environmentState = scene._environmentState;
         var renderPass = frameState.passes.render;
         environmentState.skyBoxCommand = (renderPass && defined(scene.skyBox)) ? scene.skyBox.update(frameState) : undefined;
+        environmentState.isReadyForAtmosphere = defined(scene.skyAtmosphere) && (environmentState.isReadyForAtmosphere || (defined(scene.globe) && scene.globe._surface._tilesToRender.length > 0));
         environmentState.skyAtmosphereCommand = (renderPass && defined(scene.skyAtmosphere)) ? scene.skyAtmosphere.update(frameState) : undefined;
         var sunCommands = (renderPass && defined(scene.sun)) ? scene.sun.update(scene) : undefined;
         environmentState.sunDrawCommand = defined(sunCommands) ? sunCommands.drawCommand : undefined;