Distance relative to globe surface

CesiumGS · May 20, 2020 · 95697a4 · 95697a4
1 parent dcc548f
commit 95697a4
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Showing 4 changed files with 49 additions and 3 deletions.
diff --git a/Source/Renderer/AutomaticUniforms.js b/Source/Renderer/AutomaticUniforms.js
@@ -1896,5 +1896,19 @@ var AutomaticUniforms = {
       return uniformState.ellipsoid.oneOverRadii;
     },
   }),
+
+  /**
+   * An automatic GLSL uniform that stores the camera's height above the ellipsoid.
+   *
+   * @alias czm_cameraHeight
+   * @glslUniform
+   */
+  czm_cameraHeight: new AutomaticUniform({
+    size: 1,
+    datatype: WebGLConstants.FLOAT,
+    getValue: function (uniformState) {
+      return uniformState.cameraHeight;
+    },
+  }),
 };
 export default AutomaticUniforms;
diff --git a/Source/Renderer/UniformState.js b/Source/Renderer/UniformState.js
@@ -141,6 +141,7 @@ function UniformState() {
   this._cameraDirection = new Cartesian3();
   this._cameraRight = new Cartesian3();
   this._cameraUp = new Cartesian3();
+  this._cameraHeight = 0.0;
   this._frustum2DWidth = 0.0;
   this._eyeHeight2D = new Cartesian2();
   this._pixelRatio = 1.0;
@@ -1010,6 +1011,18 @@ Object.defineProperties(UniformState.prototype, {
       return defaultValue(this._ellipsoid, Ellipsoid.WGS84);
     },
   },
+
+  /**
+   * The camera's height above the ellipsoid.
+   *
+   * @memberof UniformState.prototype
+   * #@type {Number}
+   */
+  cameraHeight: {
+    get: function () {
+      return this._cameraHeight;
+    },
+  },
 });
 
 function setView(uniformState, matrix) {
@@ -1060,6 +1073,7 @@ function setCamera(uniformState, camera) {
   Cartesian3.clone(camera.directionWC, uniformState._cameraDirection);
   Cartesian3.clone(camera.rightWC, uniformState._cameraRight);
   Cartesian3.clone(camera.upWC, uniformState._cameraUp);
+  uniformState._cameraHeight = camera.positionCartographic.height;
   uniformState._encodedCameraPositionMCDirty = true;
 }
 

diff --git a/Source/Shaders/GlobeFS.glsl b/Source/Shaders/GlobeFS.glsl
@@ -116,13 +116,13 @@ varying vec3 v_mieColor;
 #endif
 
 #ifdef UNDERGROUND_COLOR
-float interpolateByDistance(vec4 nearFarScalar)
+float interpolateByDistance(vec4 nearFarScalar, float distance)
 {
     float startDistance = nearFarScalar.x;
     float startValue = nearFarScalar.y;
     float endDistance = nearFarScalar.z;
     float endValue = nearFarScalar.w;
-    float t = clamp((v_distance - startDistance) / (endDistance - startDistance), 0.0, 1.0);
+    float t = clamp((distance - startDistance) / (endDistance - startDistance), 0.0, 1.0);
     return mix(startValue, endValue, t);
 }
 #endif
@@ -456,7 +456,9 @@ void main()
     // !gl_FrontFacing doesn't work as expected on Mac/Intel so use the more verbose form instead. See https://github.com/CesiumGS/cesium/pull/8494.
     if (gl_FrontFacing == false)
     {
-        float blendAmount = interpolateByDistance(u_undergroundColorByDistance);
+        float distanceFromEllipsoid = max(czm_cameraHeight, 0.0);
+        float distance = max(v_distance - distanceFromEllipsoid, 0.0);
+        float blendAmount = interpolateByDistance(u_undergroundColorByDistance, distance);
         vec4 undergroundColor = vec4(u_undergroundColor.rgb, u_undergroundColor.a * blendAmount);
         finalColor = alphaBlend(undergroundColor, finalColor);
     }

diff --git a/Specs/Renderer/AutomaticUniformSpec.js b/Specs/Renderer/AutomaticUniformSpec.js
@@ -1,5 +1,6 @@
 import { Cartesian2 } from "../../Source/Cesium.js";
 import { Cartesian3 } from "../../Source/Cesium.js";
+import { Cartographic } from "../../Source/Cesium.js";
 import { Color } from "../../Source/Cesium.js";
 import { defaultValue } from "../../Source/Cesium.js";
 import { DirectionalLight } from "../../Source/Cesium.js";
@@ -73,6 +74,7 @@ describe(
         ),
         rightWC: defaultValue(right, Cartesian3.clone(Cartesian3.UNIT_X)),
         upWC: defaultValue(up, Cartesian3.clone(Cartesian3.UNIT_Y)),
+        positionCartographic: new Cartographic(0.0, 0.0, 10.0),
       };
     }
 
@@ -2169,6 +2171,20 @@ describe(
         fragmentShader: fs,
       }).contextToRender();
     });
+
+    it("has czm_cameraHeight", function () {
+      var frameState = createFrameState(context, createMockCamera());
+      context.uniformState.update(frameState);
+
+      var fs =
+        "void main() { " +
+        "  gl_FragColor = vec4(czm_cameraHeight == 10.0); " +
+        "}";
+      expect({
+        context: context,
+        fragmentShader: fs,
+      }).contextToRender();
+    });
   },
   "WebGL"
 );