Introduce BufferObject API.

NOTE: after Metal and Vulkan support lands, we can potentially simplify
the Driver API by removing some of the old VertexBuffer entry points.

This introduces a new API-level object called `BufferObject`, and a new
backend-level object called `HwBufferObject`. This encapsulates a single
VBO. It's especially useful when clients need to share data between
multiple VertexBuffer objects. (e.g. for morphing).

In the future, buffer objects could perhaps be used for non-vertex data
(e.g. for compute).

The existing `VertexBuffer` class can now be configured to use buffer
objects by calling `enableBufferObjects` on the builder. By default its
API is unchanged. If buffer objects are enabled, then clients should use
`setBufferObjectAt` (which takes a buffer object) rather than
`setBufferAt` (which takes CPU data).

OpenGL is the trickiest backend for this, due to existence of VAOs.
The implementation in this PR uses a version-tracking scheme to
figure out when to update the VAO.

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

@@ -0,0 +1,99 @@
+/*
+ * Copyright (C) 2021 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
+ *
+ *      http://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.
+ */
+
+#include <jni.h>
+
+#include <functional>
+#include <stdlib.h>
+#include <string.h>
+
+#include <filament/BufferObject.h>
+
+#include <backend/BufferDescriptor.h>
+
+#include "common/CallbackUtils.h"
+#include "common/NioUtils.h"
+
+using namespace filament;
+using namespace backend;
+
+extern "C" JNIEXPORT jlong JNICALL
+Java_com_google_android_filament_BufferObject_nCreateBuilder(JNIEnv *env, jclass type) {
+    return (jlong) new BufferObject::Builder();
+}
+
+extern "C" JNIEXPORT void JNICALL
+Java_com_google_android_filament_BufferObject_nDestroyBuilder(JNIEnv *env, jclass type,
+        jlong nativeBuilder) {
+    BufferObject::Builder* builder = (BufferObject::Builder *) nativeBuilder;
+    delete builder;
+}
+
+extern "C" JNIEXPORT void JNICALL
+Java_com_google_android_filament_BufferObject_nBuilderSize(JNIEnv *env, jclass type,
+        jlong nativeBuilder, jint byteCount) {
+    BufferObject::Builder* builder = (BufferObject::Builder *) nativeBuilder;
+    builder->size((uint32_t) byteCount);
+}
+
+extern "C" JNIEXPORT void JNICALL
+Java_com_google_android_filament_BufferObject_nBuilderBindingType(JNIEnv *env, jclass type,
+        jlong nativeBuilder, jint bindingType) {
+    using BindingType = BufferObject::BindingType;
+    BufferObject::Builder* builder = (BufferObject::Builder *) nativeBuilder;
+    BindingType types[] = {BindingType::VERTEX};
+    builder->bindingType(types[bindingType]);
+}
+
+extern "C" JNIEXPORT jlong JNICALL
+Java_com_google_android_filament_BufferObject_nBuilderBuild(JNIEnv *env, jclass type,
+        jlong nativeBuilder, jlong nativeEngine) {
+    BufferObject::Builder* builder = (BufferObject::Builder *) nativeBuilder;
+    Engine *engine = (Engine *) nativeEngine;
+    return (jlong) builder->build(*engine);
+}
+
+extern "C" JNIEXPORT jint JNICALL
+Java_com_google_android_filament_BufferObject_nGetByteCount(JNIEnv *env, jclass type,
+        jlong nativeBufferObject) {
+    BufferObject *bufferObject = (BufferObject *) nativeBufferObject;
+    return (jint) bufferObject->getByteCount();
+}
+
+extern "C" JNIEXPORT int JNICALL
+Java_com_google_android_filament_BufferObject_nSetBuffer(JNIEnv *env, jclass type,
+        jlong nativeBufferObject, jlong nativeEngine, jobject buffer, int remaining,
+        jint destOffsetInBytes, jint count,
+        jobject handler, jobject runnable) {
+    BufferObject *bufferObject = (BufferObject *) nativeBufferObject;
+    Engine *engine = (Engine *) nativeEngine;
+
+    AutoBuffer nioBuffer(env, buffer, count);
+    void* data = nioBuffer.getData();
+    size_t sizeInBytes = nioBuffer.getSize();
+    if (sizeInBytes > (remaining << nioBuffer.getShift())) {
+        // BufferOverflowException
+        return -1;
+    }
+
+    auto* callback = JniBufferCallback::make(engine, env, handler, runnable, std::move(nioBuffer));
+
+    BufferDescriptor desc(data, sizeInBytes, &JniBufferCallback::invoke, callback);
+
+    bufferObject->setBuffer(*engine, std::move(desc), (uint32_t) destOffsetInBytes);
+
+    return 0;
+}