Re-add terrain and atmosphere splitting (#103)

* Re-add terrain and atmosphere splitting
* Update terrain splitter code in surface shader set. (#104)
* use bit 33 for splitTerrain
* use bitwise operator

---------

Co-authored-by: Nanda <nanda.sankaran@gmail.com>

Author: zoran995

CHANGES.md

@@ -4,6 +4,7 @@
 
 - Added `token`, `mapServerData`, and `parameters` properties to `ArcGisMapServerImageryProvider.ConstructorOptions`.
 - Added `Ion.defaultTokenMessage` to customize the credit message shown on the map when using default Ion token.
+- Added split terrain feature.
 
 ## 1.139.1 - 2026-03-05
 

packages/engine/Source/Scene/Globe.js

@@ -27,6 +27,7 @@ import ImageryLayerCollection from "./ImageryLayerCollection.js";
 import QuadtreePrimitive from "./QuadtreePrimitive.js";
 import SceneMode from "./SceneMode.js";
 import ShadowMode from "./ShadowMode.js";
+import SplitDirection from "./SplitDirection.js";
 import CesiumMath from "../Core/Math.js";
 
 /**
@@ -370,6 +371,15 @@ function Globe(ellipsoid) {
    * @default 0.3
    */
   this.vertexShadowDarkness = 0.3;
+
+  /**
+   * The {@link SplitDirection} to apply, showing the terrain only on
+   * the left or right of the splitter control.
+   *
+   * @type {SplitDirection}
+   * @default {@link SplitDirection.NONE}
+   */
+  this.splitDirection = SplitDirection.NONE;
 }
 
 Object.defineProperties(Globe.prototype, {
@@ -1055,6 +1065,7 @@ Globe.prototype.beginFrame = function (frameState) {
     tileProvider.undergroundColorAlphaByDistance =
       this._undergroundColorAlphaByDistance;
     tileProvider.lambertDiffuseMultiplier = this.lambertDiffuseMultiplier;
+    tileProvider.splitDirection = this.splitDirection;
 
     surface.beginFrame(frameState);
   }

packages/engine/Source/Scene/GlobeSurfaceShaderSet.js

@@ -134,6 +134,7 @@ GlobeSurfaceShaderSet.prototype.getShaderProgram = function (options) {
   const hasExaggeration = options.hasExaggeration;
   const showUndergroundColor = options.showUndergroundColor;
   const translucent = options.translucent;
+  const splitTerrain = options.splitTerrain;
 
   let quantization = 0;
   let quantizationDefine = "";
@@ -197,7 +198,8 @@ GlobeSurfaceShaderSet.prototype.getShaderProgram = function (options) {
       (showUndergroundColor << 30) |
       (translucent << 31)) >>>
       0) +
-    (applyDayNightAlpha ? 0x100000000 : 0);
+    (applyDayNightAlpha ? 0x100000000 : 0) +
+    (splitTerrain ? 0x200000000 : 0);
 
   let currentClippingShaderState = 0;
   if (defined(clippingPlanes) && clippingPlanes.length > 0) {
@@ -382,6 +384,10 @@ GlobeSurfaceShaderSet.prototype.getShaderProgram = function (options) {
       vs.defines.push("EXAGGERATION");
     }
 
+    if (splitTerrain) {
+      fs.defines.push("SPLIT_TERRAIN");
+    }
+
     let computeDayColor =
       "\
     vec4 computeDayColor(vec4 initialColor, vec3 textureCoordinates, float nightBlend)\n\

packages/engine/Source/Scene/GlobeSurfaceTileProvider.js

@@ -47,6 +47,7 @@ import Primitive from "./Primitive.js";
 import QuadtreeTileLoadState from "./QuadtreeTileLoadState.js";
 import SceneMode from "./SceneMode.js";
 import ShadowMode from "./ShadowMode.js";
+import SplitDirection from "./SplitDirection.js";
 import TerrainFillMesh from "./TerrainFillMesh.js";
 import TerrainState from "./TerrainState.js";
 import TileBoundingRegion from "./TileBoundingRegion.js";
@@ -91,6 +92,7 @@ function GlobeSurfaceTileProvider(options) {
   this.showGroundAtmosphere = false;
   this.shadows = ShadowMode.RECEIVE_ONLY;
   this.vertexShadowDarkness = 0.3;
+  this.splitDirection = SplitDirection.NONE;
 
   /**
    * The color to use to highlight terrain fill tiles. If undefined, fill tiles are not
@@ -1859,6 +1861,9 @@ function createTileUniformMap(frameState, globeSurfaceTileProvider) {
     u_vertexShadowDarkness: function () {
       return this.properties.vertexShadowDarkness;
     },
+    u_terrainSplitDirection: function () {
+      return globeSurfaceTileProvider.splitDirection;
+    },
 
     // make a separate object so that changes to the properties are seen on
     // derived commands that combine another uniform map with this one.
@@ -2361,6 +2366,8 @@ function addDrawCommandsForTile(tileProvider, tile, frameState) {
   surfaceShaderSetOptions.clippedByBoundaries = surfaceTile.clippedByBoundaries;
   surfaceShaderSetOptions.hasGeodeticSurfaceNormals = hasGeodeticSurfaceNormals;
   surfaceShaderSetOptions.hasExaggeration = hasExaggeration;
+  surfaceShaderSetOptions.splitTerrain =
+    tileProvider.splitDirection !== SplitDirection.NONE;
 
   const tileImageryCollection = surfaceTile.imagery;
   let imageryIndex = 0;

packages/engine/Source/Scene/SkyAtmosphere.js

@@ -21,6 +21,7 @@ import Axis from "./Axis.js";
 import BlendingState from "./BlendingState.js";
 import CullFace from "./CullFace.js";
 import SceneMode from "./SceneMode.js";
+import SplitDirection from "./SplitDirection.js";
 
 /**
  * An atmosphere drawn around the limb of the provided ellipsoid. Based on
@@ -153,6 +154,16 @@ function SkyAtmosphere(ellipsoid) {
    */
   this.brightnessShift = 0.0;
 
+  /**
+   * The {@link SplitDirection} to apply, showing the atmosphere only on
+   * the left or right of the splitter control.
+   *
+   * @type {SplitDirection}
+   * @default {@link SplitDirection.NONE}
+   */
+  this.splitDirection = SplitDirection.NONE;
+  this._splitDirection = undefined;
+
   this._hueSaturationBrightness = new Cartesian3();
 
   // outer radius, inner radius, dynamic atmosphere color flag
@@ -197,6 +208,9 @@ function SkyAtmosphere(ellipsoid) {
     u_atmosphereMieAnisotropy: function () {
       return that.atmosphereMieAnisotropy;
     },
+    u_splitDirection: function () {
+      return that.splitDirection;
+    },
   };
 }
 
@@ -298,8 +312,15 @@ SkyAtmosphere.prototype.update = function (frameState, globe) {
     });
   }
 
+  // Note that the splitDirection flag requires _two_ bits.
+  const splitDirectionFlag =
+    this.splitDirection === 0 ? 0 : this.splitDirection < 0.0 ? 1 : 2;
+
   const flags =
-    colorCorrect | (perFragmentAtmosphere << 2) | (translucent << 3);
+    colorCorrect |
+    (perFragmentAtmosphere << 2) |
+    (translucent << 3) |
+    (splitDirectionFlag << 4);
 
   if (flags !== this._flags) {
     this._flags = flags;
@@ -318,6 +339,10 @@ SkyAtmosphere.prototype.update = function (frameState, globe) {
       defines.push("GLOBE_TRANSLUCENT");
     }
 
+    if (this.splitDirection !== SplitDirection.NONE) {
+      defines.push("SPLIT_ATMOSPHERE");
+    }
+
     const vs = new ShaderSource({
       defines: defines,
       sources: [AtmosphereCommon, SkyAtmosphereCommon, SkyAtmosphereVS],

packages/engine/Source/Shaders/GlobeFS.glsl

@@ -83,6 +83,10 @@ in vec2 v_clippingPosition;
 flat in int v_regionIndex;
 #endif
 
+#ifdef SPLIT_TERRAIN
+uniform float u_terrainSplitDirection;
+#endif
+
 #if defined(GROUND_ATMOSPHERE) || defined(FOG) && defined(DYNAMIC_ATMOSPHERE_LIGHTING) && (defined(ENABLE_VERTEX_LIGHTING) || defined(ENABLE_DAYNIGHT_SHADING))
 uniform float u_minimumBrightness;
 #endif
@@ -337,6 +341,15 @@ void main()
         }
 #endif
 
+#ifdef SPLIT_TERRAIN
+    float splitPosition = czm_splitPosition;
+    if (u_terrainSplitDirection < 0.0 && gl_FragCoord.x > splitPosition) {
+        discard;
+    } else if (u_terrainSplitDirection > 0.0 && gl_FragCoord.x < splitPosition) {
+        discard;
+    }
+#endif
+
 #ifdef ENABLE_CLIPPING_PLANES
     float clipDistance = clip(gl_FragCoord, u_clippingPlanes, u_clippingPlanesMatrix);
 #endif

packages/engine/Source/Shaders/SkyAtmosphereFS.glsl

@@ -2,6 +2,10 @@ in vec3 v_outerPositionWC;
 
 uniform vec3 u_hsbShift;
 
+#ifdef SPLIT_ATMOSPHERE
+uniform float u_splitDirection;
+#endif
+
 #ifndef PER_FRAGMENT_ATMOSPHERE
 in vec3 v_mieColor;
 in vec3 v_rayleighColor;
@@ -11,6 +15,15 @@ in float v_translucent;
 
 void main (void)
 {
+    #ifdef SPLIT_ATMOSPHERE
+        float splitPosition = czm_splitPosition;
+        if (u_splitDirection < 0.0 && gl_FragCoord.x > splitPosition) {
+            discard;
+        } else if (u_splitDirection > 0.0 && gl_FragCoord.x < splitPosition) {
+            discard;
+        }
+    #endif
+
     float lightEnum = u_radiiAndDynamicAtmosphereColor.z;
     vec3 lightDirection = czm_getDynamicAtmosphereLightDirection(v_outerPositionWC, lightEnum);