Add Force Double Sided toggle to Cesium3DTileset

CHANGES.md

@@ -2,6 +2,10 @@
 
 ## ? - ?
 
+##### Additions :tada:
+
+- Added a `Force Double Sided` toggle to `Cesium3DTileset`. When enabled, all tile primitives are rendered with back-face culling disabled, regardless of the glTF material's `doubleSided` flag or the cull state of a user-supplied `Opaque Material`.
+
 ##### Fixes :wrench:
 
 - The native Android library (`libCesiumForUnityNative.so`) is now built with 16 KB ELF segment alignment, enabling compatibility with Android 15+ devices that use 16 KB memory pages.

Source/Editor/Cesium3DTilesetEditor.cs

@@ -36,6 +36,7 @@ public class Cesium3DTilesetEditor : Editor
         //private SerializedProperty _useLodTransitions;
         //private SerializedProperty _lodTransitionLength;
         private SerializedProperty _generateSmoothNormals;
+        private SerializedProperty _forceDoubleSided;
 
         private SerializedProperty _pointCloudShading;
 
@@ -85,6 +86,8 @@ private void OnEnable()
             //    this.serializedObject.FindProperty("_lodTransitionLength");
             this._generateSmoothNormals =
                 this.serializedObject.FindProperty("_generateSmoothNormals");
+            this._forceDoubleSided =
+                this.serializedObject.FindProperty("_forceDoubleSided");
             this._ignoreKhrMaterialsUnlit = this.serializedObject.FindProperty("_ignoreKhrMaterialsUnlit");
 
             this._pointCloudShading = this.serializedObject.FindProperty("_pointCloudShading");
@@ -429,6 +432,14 @@ private void DrawRenderProperties()
                 "rendered with smooth normals instead when the original glTF is missing normals.");
             EditorGUILayout.PropertyField(this._generateSmoothNormals, generateSmoothNormalsContent);
 
+            GUIContent forceDoubleSidedContent = new GUIContent(
+                "Force Double Sided",
+                "Disable back-face culling on every tile material, ignoring the " +
+                "glTF doubleSided flag. Use this when you assign a custom Opaque " +
+                "Material with double-sided rendering and don't want Cesium to " +
+                "overwrite that setting per tile.");
+            EditorGUILayout.PropertyField(this._forceDoubleSided, forceDoubleSidedContent);
+
             var ignoreKhrMaterialsUnlit = new GUIContent(
                 "Ignore KHR_materials_unlit",
                 "Whether to ignore the KHR_materials_unlit extension on the glTF tiles in "+

Source/Runtime/Cesium3DTileset.cs

@@ -589,6 +589,29 @@ public bool generateSmoothNormals
             }
         }
 
+        [SerializeField]
+        private bool _forceDoubleSided = false;
+
+        /// <summary>
+        /// When enabled, all tile primitives are rendered with back-face culling
+        /// disabled, regardless of the glTF material's doubleSided flag or the
+        /// settings on a user-supplied opaqueMaterial.
+        /// </summary>
+        /// <remarks>
+        /// Useful when assigning a custom Material whose Render Face is set to
+        /// Both - Cesium would otherwise overwrite the material's cull state from
+        /// the glTF on every tile load.
+        /// </remarks>
+        public bool forceDoubleSided
+        {
+            get => this._forceDoubleSided;
+            set
+            {
+                this._forceDoubleSided = value;
+                this.RecreateTileset();
+            }
+        }
+
         [SerializeField]
         private bool _ignoreKhrMaterialsUnlit = false;
 

Source/Runtime/ConfigureReinterop.cs

@@ -295,6 +295,7 @@ public void ExposeToCPP()
             //tileset.useLodTransitions = tileset.useLodTransitions;
             //tileset.lodTransitionLength = tileset.lodTransitionLength;
             tileset.generateSmoothNormals = tileset.generateSmoothNormals;
+            tileset.forceDoubleSided = tileset.forceDoubleSided;
             tileset.ignoreKhrMaterialsUnlit = tileset.ignoreKhrMaterialsUnlit;
             tileset.createPhysicsMeshes = tileset.createPhysicsMeshes;
             tileset.suspendUpdate = tileset.suspendUpdate;

native~/src/Runtime/UnityPrepareRendererResources.cpp

@@ -1586,6 +1586,21 @@ void* UnityPrepareRendererResources::prepareInMainThread(
               materialProperties);
         }
 
+        if (tilesetComponent.forceDoubleSided()) {
+          material.SetFloat(
+              materialProperties.getDoubleSidedEnableID(),
+              1.0f);
+          material.SetFloat(
+              materialProperties.getCullID(),
+              float(UnityEngine::Rendering::CullMode::Off));
+          material.SetFloat(
+              materialProperties.getCullModeID(),
+              float(UnityEngine::Rendering::CullMode::Off));
+          material.SetFloat(
+              materialProperties.getBuiltInCullModeID(),
+              float(UnityEngine::Rendering::CullMode::Off));
+        }
+
         if (primitiveInfo.containsPoints) {
           CesiumForUnity::CesiumPointCloudRenderer pointCloudRenderer =
               primitiveGameObject