Implement a "black board" for the framegraph

FrameGraph always keeps a default Blackboard, but additional ones 
can be created if needed.

A blackboard is just a registry of FrameGraphHandles, queryable by name.

filament/CMakeLists.txt

@@ -44,6 +44,7 @@ set(SRCS
         src/components/LightManager.cpp
         src/components/RenderableManager.cpp
         src/components/TransformManager.cpp
+        src/fg/Blackboard.cpp
         src/fg/FrameGraph.cpp
         src/fg/FrameGraphHandle.cpp
         src/fg/fg/RenderTarget.cpp
@@ -90,6 +91,7 @@ set(PRIVATE_HDRS
         src/components/LightManager.h
         src/components/RenderableManager.h
         src/components/TransformManager.h
+        src/fg/Blackboard.h
         src/fg/FrameGraph.h
         src/fg/FrameGraphPass.h
         src/fg/FrameGraphPassResources.h

filament/src/fg/Blackboard.cpp

@@ -0,0 +1,35 @@
+/*
+ * Copyright (C) 2020 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 "Blackboard.h"
+
+using namespace utils;
+
+namespace filament {
+
+FrameGraphHandle Blackboard::getHandle(utils::StaticString const& name) const noexcept {
+    auto it = mMap.find(name);
+    if (it != mMap.end()) {
+        return it.value();
+    }
+    return {};
+}
+
+void Blackboard::remove(utils::StaticString const& name) noexcept {
+    mMap.erase(name);
+}
+
+} // namespace filament

filament/src/fg/Blackboard.h

@@ -0,0 +1,55 @@
+/*
+ * Copyright (C) 2020 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.
+ */
+
+#ifndef TNT_FILAMENT_FG_BLACKBOARD_H
+#define TNT_FILAMENT_FG_BLACKBOARD_H
+
+#include "FrameGraphHandle.h"
+
+#include <utils/CString.h>
+
+#include <tsl/robin_map.h>
+
+namespace filament {
+
+class Blackboard {
+    using Container = tsl::robin_map<utils::StaticString, FrameGraphHandle>;
+
+public:
+    auto& operator [](utils::StaticString const& name) noexcept {
+        return mMap.insert_or_assign(name, FrameGraphHandle{}).first.value();
+    }
+
+    template<typename T>
+    void put(utils::StaticString const& name, FrameGraphId<T> handle) noexcept {
+        mMap.insert_or_assign(name, handle);
+    }
+
+    template<typename T>
+    FrameGraphId<T> get(utils::StaticString&& name) const noexcept {
+        return static_cast<FrameGraphId<T>>(getHandle(std::forward<utils::StaticString>(name)));
+    }
+
+    void remove(utils::StaticString const& name) noexcept;
+
+private:
+    FrameGraphHandle getHandle(utils::StaticString const& name) const noexcept;
+    Container mMap;
+};
+
+} // namespace filament
+
+#endif //TNT_FILAMENT_FG_BLACKBOARD_H

filament/src/fg/FrameGraph.h

@@ -18,6 +18,7 @@
 #define TNT_FILAMENT_FRAMEGRAPH_H
 
 
+#include "Blackboard.h"
 #include "FrameGraphPass.h"
 #include "FrameGraphHandle.h"
 #include "FrameGraphPassResources.h"
@@ -147,6 +148,9 @@ public:
     FrameGraph& operator = (FrameGraph const&) = delete;
     ~FrameGraph();
 
+    Blackboard& getBlackboard() noexcept { return mBlackboard; }
+    Blackboard const& getDefaultBlackboard() const noexcept { return mBlackboard; }
+
     struct Empty{};
 
     /*
@@ -322,6 +326,7 @@ private:
 
     FrameGraphHandle moveResource(FrameGraphHandle from, FrameGraphHandle to);
 
+    Blackboard mBlackboard;
     fg::ResourceAllocatorInterface& mResourceAllocator;
     details::LinearAllocatorArena mArena;
     Vector<fg::PassNode> mPassNodes;                    // list of frame graph passes

filament/src/fg/FrameGraphHandle.h

@@ -34,6 +34,7 @@ struct RenderTarget;
 struct RenderTargetResource;
 } // namespace fg
 
+class Blackboard;
 class FrameGraph;
 class FrameGraphPassResources;
 
@@ -64,6 +65,7 @@ class FrameGraphId;
 class FrameGraphHandle {
     template<typename T>
     friend class FrameGraphId;
+    friend class Blackboard;
     friend class FrameGraph;
     friend class FrameGraphPassResources;
     friend struct fg::PassNode;