Add snippet for Jetpack Scenecore material overrides in XR (#759)

* Add snippet for Jetpack Scenecore material overrides in XR

---------

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: amyZepp

xr/src/main/java/com/example/xr/scenecore/MaterialOverride.kt

@@ -0,0 +1,84 @@
+/*
+ * Copyright 2025 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.example.xr.scenecore
+
+import androidx.xr.runtime.Session
+import androidx.xr.runtime.math.Vector4
+import androidx.xr.scenecore.AlphaMode
+import androidx.xr.scenecore.GltfModelEntity
+import androidx.xr.scenecore.KhronosPbrMaterial
+import androidx.xr.scenecore.Texture
+import kotlin.io.path.Path
+
+private class MaterialOverride(val xrSession: Session) {
+    private suspend fun createMaterial() {
+        // [START androidxr_scenecore_material_override_createMaterial]
+        val pbrMaterial = KhronosPbrMaterial.create(
+            session = xrSession,
+            alphaMode = AlphaMode.OPAQUE
+        )
+        // [END androidxr_scenecore_material_override_createMaterial]
+    }
+
+    private fun setBaseColor(pbrMaterial: KhronosPbrMaterial) {
+        // [START androidxr_scenecore_material_override_setBaseColor]
+        pbrMaterial.setBaseColorFactor(
+            Vector4(
+                x = 0.5f,
+                y = 0.0f,
+                z = 0.5f,
+                w = 0.0f
+            )
+        )
+        // [END androidxr_scenecore_material_override_setBaseColor]
+    }
+
+    private suspend fun createTexture() {
+        // [START androidxr_scenecore_material_override_createTexture]
+        val texture = Texture.create(
+            session = xrSession,
+            path = Path("textures/texture_file.png")
+        )
+        // [END androidxr_scenecore_material_override_createTexture]
+    }
+
+    private fun setOcclusionTexture(pbrMaterial: KhronosPbrMaterial, texture: Texture) {
+        // [START androidxr_scenecore_material_override_setOcclusionTexture]
+        pbrMaterial.setOcclusionTexture(
+            texture = texture,
+            strength = 1.0f
+        )
+        // [END androidxr_scenecore_material_override_setOcclusionTexture]
+    }
+
+    private fun setMaterialOverride(gltfModelEntity: GltfModelEntity, pbrMaterial: KhronosPbrMaterial) {
+        // [START androidxr_scenecore_material_override_setMaterialOverride]
+        gltfModelEntity.setMaterialOverride(
+            material = pbrMaterial,
+            nodeName = "Node Name"
+        )
+        // [END androidxr_scenecore_material_override_setMaterialOverride]
+    }
+
+    private fun clearMaterialOverride(gltfModelEntity: GltfModelEntity) {
+        // [START androidxr_scenecore_material_override_clearMaterialOverride]
+        gltfModelEntity.clearMaterialOverride(
+            nodeName = "Node Name"
+        )
+        // [END androidxr_scenecore_material_override_clearMaterialOverride]
+    }
+}