Merge pull request #8470 from AnalyticalGraphicsInc/terrain-back-face-culling

Looks good to me, thanks @lilleyse

Author: IanLilleyT

CHANGES.md

@@ -9,6 +9,9 @@ Change Log
 * Fixed primitive culling when below the ellipsoid but above terrain. [#8398](https://github.com/AnalyticalGraphicsInc/cesium/pull/8398)
 * Improved the translucency calculation for the Water material type. [#8455](https://github.com/AnalyticalGraphicsInc/cesium/pull/8455)
 
+##### Additions :tada:
+* Added `Globe.backFaceCulling` to support viewing terrain from below the surface. [#8470](https://github.com/AnalyticalGraphicsInc/cesium/pull/8470)
+
 ### 1.64.0 - 2019-12-02
 
 ##### Fixes :wrench:

Source/Scene/Globe.js

@@ -250,6 +250,14 @@ import TileSelectionResult from './TileSelectionResult.js';
          */
         this.atmosphereBrightnessShift = 0.0;
 
+        /**
+         * Whether to cull back-facing terrain. Set this to false when viewing terrain from below the surface.
+         *
+         * @type {Boolean}
+         * @default true
+         */
+        this.backFaceCulling = true;
+
         this._oceanNormalMap = undefined;
         this._zoomedOutOceanSpecularIntensity = undefined;
     }
@@ -739,7 +747,7 @@ import TileSelectionResult from './TileSelectionResult.js';
             tileProvider.saturationShift = this.atmosphereSaturationShift;
             tileProvider.brightnessShift = this.atmosphereBrightnessShift;
             tileProvider.fillHighlightColor = this.fillHighlightColor;
-
+            tileProvider.backFaceCulling = this.backFaceCulling;
             surface.beginFrame(frameState);
         }
     };

Source/Scene/GlobeSurfaceTileProvider.js

@@ -4,6 +4,7 @@ import Cartesian2 from '../Core/Cartesian2.js';
 import Cartesian3 from '../Core/Cartesian3.js';
 import Cartesian4 from '../Core/Cartesian4.js';
 import Cartographic from '../Core/Cartographic.js';
+import clone from '../Core/clone.js';
 import Color from '../Core/Color.js';
 import ColorGeometryInstanceAttribute from '../Core/ColorGeometryInstanceAttribute.js';
 import combine from '../Core/combine.js';
@@ -100,13 +101,17 @@ import TileSelectionResult from './TileSelectionResult.js';
         this.saturationShift = 0.0;
         this.brightnessShift = 0.0;
 
+        this.backFaceCulling = true;
+
         this._quadtree = undefined;
         this._terrainProvider = options.terrainProvider;
         this._imageryLayers = options.imageryLayers;
         this._surfaceShaderSet = options.surfaceShaderSet;
 
         this._renderState = undefined;
         this._blendRenderState = undefined;
+        this._disableCullingRenderState = undefined;
+        this._disableCullingBlendRenderState = undefined;
 
         this._errorEvent = new Event();
 
@@ -405,6 +410,16 @@ import TileSelectionResult from './TileSelectionResult.js';
             });
         }
 
+        if (!this.backFaceCulling && !defined(this._disableCullingRenderState)) {
+            var rs = clone(this._renderState, true);
+            rs.cull.enabled = false;
+            this._disableCullingRenderState = RenderState.fromCache(rs);
+
+            rs = clone(this._blendRenderState, true);
+            rs.cull.enabled = false;
+            this._disableCullingBlendRenderState = RenderState.fromCache(rs);
+        }
+
         // If this frame has a mix of loaded and fill tiles, we need to propagate
         // loaded heights to the fill tiles.
         if (this._hasFillTilesThisFrame && this._hasLoadedTilesThisFrame) {
@@ -1652,8 +1667,8 @@ import TileSelectionResult from './TileSelectionResult.js';
         var imageryIndex = 0;
         var imageryLen = tileImageryCollection.length;
 
-        var firstPassRenderState = tileProvider._renderState;
-        var otherPassesRenderState = tileProvider._blendRenderState;
+        var firstPassRenderState = tileProvider.backFaceCulling ? tileProvider._renderState : tileProvider._disableCullingRenderState;
+        var otherPassesRenderState = tileProvider.backFaceCulling ? tileProvider._blendRenderState : tileProvider._disableCullingBlendRenderState;
         var renderState = firstPassRenderState;
 
         var initialColor = tileProvider._firstPassInitialColor;

Specs/Scene/GlobeSpec.js

@@ -259,4 +259,19 @@ describe('Scene/Globe', function() {
             });
         });
     });
+
+    it('applies back face culling', function() {
+        scene.camera.setView({ destination : new Rectangle(0.0001, 0.0001, 0.0025, 0.0025) });
+
+        return updateUntilDone(globe).then(function() {
+            globe.backFaceCulling = true;
+            scene.render();
+            var command = scene.frameState.commandList[0];
+            expect(command.renderState.cull.enabled).toBe(true);
+            globe.backFaceCulling = false;
+            scene.render();
+            command = scene.frameState.commandList[0];
+            expect(command.renderState.cull.enabled).toBe(false);
+        });
+    });
 }, 'WebGL');