Added UI option to generate tangents

Author: david-lively

Editor/Cesium3DTilesetEditor.cs

@@ -35,6 +35,7 @@ public class Cesium3DTilesetEditor : Editor
         //private SerializedProperty _useLodTransitions;
         //private SerializedProperty _lodTransitionLength;
         private SerializedProperty _generateSmoothNormals;
+        private SerializedProperty _generateTangents;
 
         private SerializedProperty _pointCloudShading;
 
@@ -84,6 +85,9 @@ private void OnEnable()
             //    this.serializedObject.FindProperty("_lodTransitionLength");
             this._generateSmoothNormals =
                 this.serializedObject.FindProperty("_generateSmoothNormals");
+            this._generateTangents =
+                this.serializedObject.FindProperty("_generateTangents");
+
             this._ignoreKhrMaterialsUnlit = this.serializedObject.FindProperty("_ignoreKhrMaterialsUnlit");
 
             this._pointCloudShading = this.serializedObject.FindProperty("_pointCloudShading");
@@ -428,6 +432,12 @@ private void DrawRenderProperties()
                 );
             EditorGUILayout.PropertyField(this._generateSmoothNormals, generateSmoothNormalsContent);
 
+            var generateTangentsContent = new GUIContent(
+                "Generate Tangents",
+                "Whether to generate per-vertex tangets if they are missing in the source glTF."
+            );
+            EditorGUILayout.PropertyField(this._generateTangents, generateTangentsContent);
+
             var ignoreKhrMaterialsUnlitContent = new GUIContent(
                 "Ignore KHR_materials_unlit",
                 "Whether to ignore the KHR_materials_unlit extension on the glTF tiles in "+

Editor/ConfigureReinterop.cs

@@ -252,4 +252,4 @@ public void ExposeToCPP()
             var exceptionMessage = exception.Message;
         }
     }
-}
+}

Runtime/Cesium3DTileset.cs

@@ -587,6 +587,31 @@ public bool generateSmoothNormals
             }
         }
 
+        [SerializeField]
+        private bool _generateTangents = false;
+
+        /// <summary>
+        /// Whether to generate per-vertex tangents when tangents are missing in the glTF.
+        /// </summary>
+        /// <remarks>
+        /// The glTF 2.0 specification suggests that tangents should be generated when they 
+        /// are missing. 
+        /// "When tangents are not specified, client implementations SHOULD calculate tangents using 
+        /// default MikkTSpace algorithms with the specified vertex positions, normals, and texture 
+        /// coordinates associated with the normal texture."
+        /// </remarks>
+        /// <seealso cref="https://registry.khronos.org/glTF/specs/2.0/glTF-2.0.html"/>
+
+        public bool generateTangents
+        {
+            get => _generateTangents;
+            set
+            {
+                this._generateSmoothNormals = value;
+                this.RecreateTileset();
+            }
+        }
+
         [SerializeField]
         private bool _ignoreKhrMaterialsUnlit = false;
 

Runtime/ConfigureReinterop.cs

@@ -279,6 +279,7 @@ public void ExposeToCPP()
             //tileset.useLodTransitions = tileset.useLodTransitions;
             //tileset.lodTransitionLength = tileset.lodTransitionLength;
             tileset.generateSmoothNormals = tileset.generateSmoothNormals;
+            tileset.generateTangents = tileset.generateTangents;
             tileset.ignoreKhrMaterialsUnlit = tileset.ignoreKhrMaterialsUnlit;
             tileset.createPhysicsMeshes = tileset.createPhysicsMeshes;
             tileset.suspendUpdate = tileset.suspendUpdate;
@@ -949,3 +950,4 @@ Cesium3DTilesetLoadFailureDetails tilesetDetails
         }
     }
 }
+

Runtime/Resources/CesiumDefaultTilesetMaterial.mat

@@ -100,7 +100,7 @@ Material:
     - _AlphaCutoffEnable: 1
     - _AlphaDstBlend: 0
     - _AlphaSrcBlend: 1
-    - _AlphaToMask: 0
+    - _AlphaToMask: 1
     - _AlphaToMaskInspectorValue: 0
     - _BUILTIN_AlphaClip: 1
     - _BUILTIN_Blend: 0