Add JNI for TransformManager.getChildCount(), TransformManager.getChildren() and Scene.hasEntity() (#6007)

* Add JNI for TransformManager.getChildCount(), TransformManager.getChildren() and scene.hasEntity()

* Update RELEASE_NOTES.md

* Fixes

* Change getChildren to take a nullable array

* Remove no params TransformManager.getChildren()

* Update RELEASE_NOTES.md

Co-authored-by: Ben Doherty <benjdoherty15@gmail.com>
Co-authored-by: Ben Doherty <bendoherty@google.com>

RELEASE_NOTES.md

@@ -5,6 +5,7 @@ A new header is inserted each time a *tag* is created.
 
 ## main branch
 
+- Java: add methods for TransformManager.getChildCount(), TransformManager.getChildren() and Scene.hasEntity()
 - engine: Fix stencil buffer writes with OpenGL backend.
 
 ## v1.27.0

android/filament-android/src/main/cpp/Scene.cpp

@@ -83,3 +83,11 @@ Java_com_google_android_filament_Scene_nGetLightCount(JNIEnv *env, jclass type,
     Scene* scene = (Scene*) nativeScene;
     return (jint) scene->getLightCount();
 }
+
+extern "C" JNIEXPORT jboolean JNICALL
+Java_com_google_android_filament_Scene_nHasEntity(JNIEnv *env, jclass type, jlong nativeScene,
+        jint entityId) {
+    Scene* scene = (Scene*) nativeScene;
+    Entity entity = Entity::import(entityId);
+    return (jboolean) scene->hasEntity(entity);
+}

android/filament-android/src/main/cpp/TransformManager.cpp

@@ -110,6 +110,26 @@ Java_com_google_android_filament_TransformManager_nGetParent(JNIEnv*, jclass,
     return tm->getParent((TransformManager::Instance) i).getId();
 }
 
+extern "C" JNIEXPORT jint JNICALL
+Java_com_google_android_filament_TransformManager_nGetChildCount(JNIEnv*, jclass,
+        jlong nativeTransformManager, jint i) {
+    TransformManager* tm = (TransformManager*) nativeTransformManager;
+    return tm->getChildCount((TransformManager::Instance) i);
+}
+
+extern "C" JNIEXPORT void JNICALL
+Java_com_google_android_filament_TransformManager_nGetChildren(JNIEnv* env,
+        jclass, jlong nativeTransformManager, jint i,
+        jintArray outEntities_, jint count) {
+    TransformManager* tm = (TransformManager*) nativeTransformManager;
+    jint* entities = env->GetIntArrayElements(outEntities_, nullptr);
+    // This is very very gross, we just pretend Entity is just like an jint
+    // (which it is), but still.
+    tm->getChildren((TransformManager::Instance) i,
+            reinterpret_cast<Entity *>(entities), (size_t) count);
+    env->ReleaseIntArrayElements(outEntities_, entities, JNI_ABORT);
+}
+
 extern "C" JNIEXPORT void JNICALL
 Java_com_google_android_filament_TransformManager_nSetTransform(JNIEnv* env,
         jclass, jlong nativeTransformManager, jint i,

android/filament-android/src/main/java/com/google/android/filament/Scene.java

@@ -163,6 +163,15 @@ public class Scene {
         return nGetLightCount(getNativeObject());
     }
 
+    /**
+     * Returns true if the given entity is in the Scene.
+     *
+     * @return Whether the given entity is in the Scene.
+     */
+    public boolean hasEntity(@Entity int entity) {
+        return nHasEntity(getNativeObject(), entity);
+    }
+
     public long getNativeObject() {
         if (mNativeObject == 0) {
             throw new IllegalStateException("Calling method on destroyed Scene");
@@ -182,4 +191,5 @@ public class Scene {
     private static native void nRemoveEntities(long nativeScene, int[] entities);
     private static native int nGetRenderableCount(long nativeScene);
     private static native int nGetLightCount(long nativeScene);
+    private static native boolean nHasEntity(long nativeScene, int entity);
 }

android/filament-android/src/main/java/com/google/android/filament/TransformManager.java

@@ -16,6 +16,7 @@
 
 package com.google.android.filament;
 
+import androidx.annotation.IntRange;
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import androidx.annotation.Size;
@@ -199,6 +200,36 @@ import androidx.annotation.Size;
         return nGetParent(mNativeObject, i);
     }
 
+    /**
+     * Returns the number of children of an {@link EntityInstance}.
+     *
+     * @param i the {@link EntityInstance} of the transform component to query.
+     * @return The number of children of the queried component.
+     */
+    public int getChildCount(@EntityInstance int i) {
+        return nGetChildCount(mNativeObject, i);
+    }
+
+    /**
+     * Gets a list of children for a transform component.
+     *
+     * @param i           the {@link EntityInstance} of the transform component to get the children
+     *                    from.
+     * @param outEntities array to receive the result sized to the maximum number of children to
+     *                    retrieve. If <code>null</code> is given, a new suitable array sized to
+     *                    {@link #getChildCount(int)} is allocated.
+     * @return Array of retrieved children {@link Entity}.
+     */
+    public @Entity @NonNull int[] getChildren(@EntityInstance int i, @Nullable int[] outEntities) {
+        if (outEntities == null) {
+            outEntities = new int[getChildCount(i)];
+        }
+        if (outEntities.length > 0) {
+            nGetChildren(mNativeObject, i, outEntities, outEntities.length);
+        }
+        return outEntities;
+    }
+
     /**
      * Sets a local transform of a transform component.
      * <p>This operation can be slow if the hierarchy of transform is too deep, and this
@@ -360,6 +391,8 @@ import androidx.annotation.Size;
     private static native void nDestroy(long nativeTransformManager, int entity);
     private static native void nSetParent(long nativeTransformManager, int i, int newParent);
     private static native int nGetParent(long nativeTransformManager, int i);
+    private static native int nGetChildCount(long nativeTransformManager, int i);
+    private static native void nGetChildren(long nativeEntityManager, int i, int[] outEntities, int count);
     private static native void nSetTransform(long nativeTransformManager, int i, float[] localTransform);
     private static native void nSetTransformFp64(long nativeTransformManager, int i, double[] localTransform);
     private static native void nGetTransform(long nativeTransformManager, int i, float[] outLocalTransform);