text: #include <utility>
  
  /*
   * Copyright (C) 2018 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_BACKEND_PRIVATE_COMMANDSTREAM_H
  #define TNT_FILAMENT_BACKEND_PRIVATE_COMMANDSTREAM_H
  
  #include "private/backend/CircularBuffer.h"
  
  #include <backend/BufferDescriptor.h>
  #include <backend/Handle.h>
  #include <backend/PipelineState.h>
  #include <backend/PixelBufferDescriptor.h>
  #include <backend/PresentCallable.h>
  #include <backend/TargetBufferInfo.h>
  
  #include "private/backend/Program.h"
  #include "private/backend/SamplerGroup.h"
  
  // FIXME: we'd like to not need this header here.
  #include "private/backend/Driver.h"
  
  #include <backend/DriverEnums.h>
  
  
  #include <utils/compiler.h>
  
  #include <functional>
  #include <tuple>
  #include <thread>
  #include <utility>
  
  #include <cassert>
  #include <cstddef>
  #include <cstdint>
  
  // Set to true to print every commands out on log.d. This requires RTTI and DEBUG
  #define DEBUG_COMMAND_STREAM false
  
  namespace filament {
  namespace backend {
  
  class Driver;
  class CommandBase;
  
  /*
   * Dispatcher is a data structure containing only function pointers.
   * Each function pointer targets code that unpacks the arguments to the driver's method and
   * calls it.
   *
   * Dispatcher's function pointers are populated during initialization and no CommandStream calls
   * can be made before that.
   *
   * When a command is inserted into the stream, the corresponding function pointer is copied
   * directly into CommandBase from Dispatcher.
   */
  class Dispatcher {
  public:
      using Execute = void (*)(Driver& driver, CommandBase* self, intptr_t* next);
  #define DECL_DRIVER_API_SYNCHRONOUS(RetType, methodName, paramsDecl, params)
  #define DECL_DRIVER_API(methodName, paramsDecl, params)                     Execute methodName##_;
  #define DECL_DRIVER_API_RETURN(RetType, methodName, paramsDecl, params)     Execute methodName##_;
  #include "DriverAPI.inc"
  };
  
  // ------------------------------------------------------------------------------------------------
  
  class CommandBase {
      static constexpr size_t FILAMENT_OBJECT_ALIGNMENT = alignof(std::max_align_t);
  
  protected:
      using Execute = Dispatcher::Execute;
  
      constexpr explicit CommandBase(Execute execute) noexcept : mExecute(execute) {}
  
  public:
      // alignment of all Commands in the CommandStream
      static constexpr size_t align(size_t v) {
          return (v + (FILAMENT_OBJECT_ALIGNMENT - 1)) & -FILAMENT_OBJECT_ALIGNMENT;
      }
  
      // executes this command and returns the next one
      inline CommandBase* execute(Driver& driver) {
          // it is important to return the next command offset by output parameter instead
          // of return value -- it allows the compiler to perform the tail call optimization.
          intptr_t next;
          mExecute(driver, this, &next);
          return reinterpret_cast<CommandBase*>(reinterpret_cast<intptr_t>(this) + next);
      }
  
      inline ~CommandBase() noexcept = default;
  
  private:
      Execute mExecute;
  };
  
  // ------------------------------------------------------------------------------------------------
  
  template<typename T, typename Type, typename D, typename ... ARGS>
  constexpr decltype(auto) invoke(Type T::* m, D&& d, ARGS&& ... args) {
      static_assert(std::is_base_of<T, std::decay_t<D>>::value,
              "member function and object not related");
      return (std::forward<D>(d).*m)(std::forward<ARGS>(args)...);
  }
  
  template<typename M, typename D, typename T, std::size_t... I>
  constexpr decltype(auto) trampoline(M&& m, D&& d, T&& t, std::index_sequence<I...>) {
      return invoke(std::forward<M>(m), std::forward<D>(d), std::get<I>(std::forward<T>(t))...);
  }
  
  template<typename M, typename D, typename T>
  constexpr decltype(auto) apply(M&& m, D&& d, T&& t) {
      return trampoline(std::forward<M>(m), std::forward<D>(d), std::forward<T>(t),
              std::make_index_sequence< std::tuple_size<std::remove_reference_t<T>>::value >{});
  }
  
  /*
   * CommandType<> is just a wrapper class to specialize on a pointer-to-member of Driver
   * (i.e. a method pointer to a method of Driver of a particular type -- but not the
   * method itself). We only do that so we can identify the parameters of that method.
   * We won't call through that pointer though.
   */
  template<typename... ARGS>
  struct CommandType;
  
  template<typename... ARGS>
  struct CommandType<void (Driver::*)(ARGS...)> {
  
      /*
       * Command is templated on a specific method of Driver, using CommandType's template
       * parameter.
       * Note that we're never calling this method (which is why it doesn't appear in the
       * template parameter below). The actual call is made through Command::execute().
       */
      template<void(Driver::*)(ARGS...)>
      class Command : public CommandBase {
          // We use a std::tuple<> to record the arguments passed to the constructor
          using SavedParameters = std::tuple<std::remove_reference_t<ARGS>...>;
          SavedParameters mArgs;
  
          void log() noexcept;
          template<std::size_t... I> void log(std::index_sequence<I...>) noexcept;
  
      public:
          template<typename M, typename D>
          static inline void execute(M&& method, D&& driver, CommandBase* base, intptr_t* next) noexcept {
              Command* self = static_cast<Command*>(base);
              *next = align(sizeof(Command));
  #if DEBUG_COMMAND_STREAM
                  // must call this before invoking the method
                  self->log();
  #endif
              apply(std::forward<M>(method), std::forward<D>(driver), std::move(self->mArgs));
              self->~Command();
          }
  
          // A command can be moved
          inline Command(Command&& rhs) noexcept = default;
  
          template<typename... A>
          inline explicit constexpr Command(Execute execute, A&& ... args)
                  : CommandBase(execute), mArgs(std::forward<A>(args)...) {
          }
  
          // placement new declared as "throw" to avoid the compiler's null-check
          inline void* operator new(std::size_t size, void* ptr) {
              assert_invariant(ptr);
              return ptr;
          }
      };
  };
  
  // convert an method of "class Driver" into a Command<> type
  #define COMMAND_TYPE(method) CommandType<decltype(&Driver::method)>::Command<&Driver::method>
  
  // ------------------------------------------------------------------------------------------------
  
  class CustomCommand : public CommandBase {
      std::function<void()> mCommand;
      static void execute(Driver&, CommandBase* base, intptr_t* next) noexcept;
  public:
      inline CustomCommand(CustomCommand&& rhs) = default;
      inline explicit CustomCommand(std::function<void()> cmd)
              : CommandBase(execute), mCommand(std::move(cmd)) { }
  };
  
  // ------------------------------------------------------------------------------------------------
  
  class NoopCommand : public CommandBase {
      intptr_t mNext;
      static void execute(Driver&, CommandBase* self, intptr_t* next) noexcept {
          *next = static_cast<NoopCommand*>(self)->mNext;
      }
  public:
      inline constexpr explicit NoopCommand(void* next) noexcept
              : CommandBase(execute), mNext(size_t((char *)next - (char *)this)) { }
  };
  
  // ------------------------------------------------------------------------------------------------
  
  #if !defined(NDEBUG) || (FILAMENT_DEBUG_COMMANDS >= FILAMENT_DEBUG_COMMANDS_ENABLE)
      // For now, simply pass the method name down as a string and throw away the parameters.
      // This is good enough for certain debugging needs and we can improve this later.
      #define DEBUG_COMMAND_BEGIN(methodName, sync, ...) mDriver->debugCommandBegin(this, sync, #methodName)
      #define DEBUG_COMMAND_END(methodName, sync) mDriver->debugCommandEnd(this, sync, #methodName)
  #else
      #define DEBUG_COMMAND_BEGIN(methodName, sync, ...)
      #define DEBUG_COMMAND_END(methodName, sync)
  #endif
  
  class CommandStream {
      // Dispatcher could be a value (instead of pointer), which saves a load when writing commands
      // at the expense of a larger CommandStream object (about ~400 bytes)
      Dispatcher* mDispatcher = nullptr;
      Driver* mDriver = nullptr;
      CircularBuffer* UTILS_RESTRICT mCurrentBuffer = nullptr;
  
  #ifndef NDEBUG
      // just for debugging...
      std::thread::id mThreadId{};
  #endif
  
      bool mUsePerformanceCounter = false;
  
      template<typename T>
      struct AutoExecute {
          T closure;
          inline AutoExecute(T&& closure) : closure(std::forward<T>(closure)) {}
          inline ~AutoExecute() { closure(); }
      };
  
  public:
  #define DECL_DRIVER_API(methodName, paramsDecl, params)                                         \
      inline void methodName(paramsDecl) {                                                        \
          DEBUG_COMMAND_BEGIN(methodName, false, params);                                         \
          using Cmd = COMMAND_TYPE(methodName);                                                   \
          void* const p = allocateCommand(CommandBase::align(sizeof(Cmd)));                       \
          new(p) Cmd(mDispatcher->methodName##_, APPLY(std::move, params));                       \
          DEBUG_COMMAND_END(methodName, false);                                                   \
      }
  
  #define DECL_DRIVER_API_SYNCHRONOUS(RetType, methodName, paramsDecl, params)                    \
      inline RetType methodName(paramsDecl) {                                                     \
          DEBUG_COMMAND_BEGIN(methodName, true, params);                                          \
          AutoExecute callOnExit([=](){                                                           \
              DEBUG_COMMAND_END(methodName, true);                                                \
          });                                                                                     \
          return apply(&Driver::methodName, *mDriver, std::forward_as_tuple(params));             \
      }
  
  #define DECL_DRIVER_API_RETURN(RetType, methodName, paramsDecl, params)                         \
      inline RetType methodName(paramsDecl) {                                                     \
          DEBUG_COMMAND_BEGIN(methodName, false, params);                                         \
          RetType result = mDriver->methodName##S();                                              \
          using Cmd = COMMAND_TYPE(methodName##R);                                                \
          void* const p = allocateCommand(CommandBase::align(sizeof(Cmd)));                       \
          new(p) Cmd(mDispatcher->methodName##_, RetType(result), APPLY(std::move, params));      \
          DEBUG_COMMAND_END(methodName, false);                                                   \
          return result;                                                                          \
      }
  
  #include "DriverAPI.inc"
  
  public:
      CommandStream() noexcept = default;
      CommandStream(Driver& driver, CircularBuffer& buffer) noexcept;
  
      // This is for debugging only. Currently CircularBuffer can only be written from a
      // single thread. In debug builds we assert this condition.
      // Call this first in the render loop.
      inline void debugThreading() noexcept {
  #ifndef NDEBUG
          mThreadId = std::this_thread::get_id();
  #endif
      }
  
      void execute(void* buffer);
  
      /*
       * queueCommand() allows to queue a lambda function as a command.
       * This is much less efficient than using the Driver* API.
       */
      void queueCommand(std::function<void()> command);
  
      /*
       * Allocates memory associated to the current CommandStreamBuffer.
       * This memory will be automatically freed after this command buffer is processed.
       * IMPORTANT: Destructors ARE NOT called
       */
      inline void* allocate(size_t size, size_t alignment = 8) noexcept;
  
      /*
       * Helper to allocate an array of trivially destructible objects
       */
      template<typename PodType,
              typename = typename std::enable_if<std::is_trivially_destructible<PodType>::value>::type>
      inline PodType* allocatePod(
              size_t count = 1, size_t alignment = alignof(PodType)) noexcept;
  
  private:
      inline void* allocateCommand(size_t size) {
          assert_invariant(mThreadId == std::this_thread::get_id());
          return mCurrentBuffer->allocate(size);
      }
  };
  
  void* CommandStream::allocate(size_t size, size_t alignment) noexcept {
      // make sure alignment is a power of two
      assert_invariant(alignment && !(alignment & alignment-1));
  
      // pad the requested size to accommodate NoopCommand and alignment
      const size_t s = CustomCommand::align(sizeof(NoopCommand) + size + alignment - 1);
  
      // allocate space in the command stream and insert a NoopCommand
      char* const p = (char *)allocateCommand(s);
      new(p) NoopCommand(p + s);
  
      // calculate the "user" data pointer
      void* data = (void *)((uintptr_t(p) + sizeof(NoopCommand) + alignment - 1) & ~(alignment - 1));
      assert_invariant(data >= p + sizeof(NoopCommand));
      return data;
  }
  
  template<typename PodType, typename>
  PodType* CommandStream::allocatePod(size_t count, size_t alignment) noexcept {
      return static_cast<PodType*>(allocate(count * sizeof(PodType), alignment));
  }
  
  } // namespace backend
  } // namespace filament
  
  #endif // TNT_FILAMENT_BACKEND_PRIVATE_COMMANDSTREAM_H
  