add GPU morpher + Dart API

ios/src/morph/GPUMorphHelper.h

@@ -0,0 +1,87 @@
+/*
+ * 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 "FFilamentAsset.h"
+#include "FFilamentInstance.h"
+#include "filament/Texture.h"
+#include "filament/Engine.h"
+#include <math/vec4.h>
+
+#include <tsl/robin_map.h>
+
+#include <vector>
+
+using namespace filament;
+
+struct cgltf_node;
+struct cgltf_mesh;
+struct cgltf_primitive;
+
+namespace gltfio {
+
+  ///
+  /// A GPUMorphHelper instance can be created per mesh (this avoids creating textures for meshes that do not require animation).
+  /// For each primitive in the mesh, a texture is created to store the target positions and normals.
+  /// The texture is laid out as x * 1 * z, where z is the number of morph targets and x is the number of vertices for the primitive.
+  /// A MaterialInstance is created for each primitive, then applied to the entity identified by entityName.
+  ///
+    class GPUMorphHelper {
+    public:
+        using Entity = utils::Entity;
+
+        GPUMorphHelper(FFilamentAsset *asset, const char* meshName, const char* entityName, const char* materialInstanceName);
+
+        ~GPUMorphHelper();
+
+        void applyWeights(float const *weights, size_t count, int primitiveIndex) noexcept;
+
+    private:
+        struct GltfTarget {
+            const void *bufferObject;
+            uint32_t bufferSize;
+            int morphTargetIndex;
+            cgltf_attribute_type type;
+        };
+
+        struct GltfPrimitive {
+            filament::VertexBuffer *vertexBuffer;
+            Texture* texture;
+            std::vector <GltfTarget> targets; // TODO: flatten this?
+            const char* materialName;
+            cgltf_size numTargets = 0;
+            cgltf_size numVertices = 0;
+            MaterialInstance* materialInstance = nullptr;
+        };
+
+        struct TableEntry {
+            std::vector <GltfPrimitive> primitives; // TODO: flatten this?
+        };
+
+        int numAttributes = 2; // position & normal
+
+        uint32_t* indicesBuffer = nullptr;
+
+        void addPrimitive(cgltf_mesh const *mesh, int primitiveIndex, TableEntry *entry);
+
+        void createTextures();
+
+
+        cgltf_mesh const* targetMesh;
+
+        tsl::robin_map <Entity, TableEntry> mMorphTable;
+        FFilamentAsset *mAsset;
+    };
+}