Google Filament 渲染引擎(2)-Backend 核心类先容

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Google Filament 渲染引擎(2)-Backend 核心类先容


阅读分析:


  • 本文基于 filament 版本: v1.58.0
  • 文本更加论述 Backend 内部核心类的关系, 示例代码作了非常多的删减和简化
文本将以创建纹理为例, 论述 Backend 内部的流程。后端图形接口以 OpenGL 为例。
核心类的功能概览:


  • Dispatcher: 本质上只是一个函数指针的集合，用于将命令与驱动接口的方法绑定。在初始化阶段，这些函数指针就被填充好。
  • Driver: 负责管理底层驱动的状态，以及与硬件交互的详细实现。
  • CommandStream: 负责接收命令，并将其发送到驱动。
  • Command: 命令对象，包含了详细的命令类型和参数, 负责命令的封装和执行.
  • Engine: 负责管理资源的创建和烧毁，以及命令的提交。
一、底层驱动初始化

  1. // --------------------------------- step1: 创建 Driver ----------------------------------
  2. Backend mBackend = Backend::OPENGL;
  3. // 根据类型选择平台, 以 PlatformCocoaGL 为例
  4. PlatformCocoaGL platform = filament::backend::PlatformFactory::create(&mBackend);
  6. // 根据平台创建驱动, 这里 driver 的类型是 OpenGLDriver
  7. Driver* driver = platform->createDriver();
  9. // --------------------------------- step2: 创建 CommandStream ----------------------------------
  10. using DriverApi = filament::backend::CommandStream;
  11. // 这里完成 底层驱动 绑定到 CommandStream 的 Dispatcher 上
  12. DriverApi* driverApi = new DriverApi(*driver);
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二、创建纹理

应用层创建代码:
  1. filament::Texture* texture = Texture::Builder()
  2.     .levels(1)
  3.     .sampler(Texture::Sampler::SAMPLER_EXTERNAL)
  4.     .build(*mEngine);
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  1. Texture* Texture::Builder::build(Engine& engine) {
  2.     // 调用 Engine 的 createTexture 方法
  3.     return downcast(engine).createTexture(*this);
  4. }
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三、核心类

1、Engine

  1. // ====> 模板展开后的 createTexture 函数
  2. FTexture* FEngine::createTexture(const Texture::Builder& builder) noexcept {
  3.     // 展开 create 模板调用
  4.     FTexture* p = mHeapAllocator.make<FTexture>(*this, builder);
  5.     if (p) {
  6.         mTextures.insert(p);
  7.     }
  8.     return p;
  9. }
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  1. FTexture::FTexture() {
  2.     backend::Handle<backend::HwTexture> mHandle;
  4.     // driver 的实际类型是 CommandStream
  5.     FEngine::DriverApi& driver = engine.getDriverApi();
  6.     mHandle = driver.createTexture(
  7.                 mTarget, mLevelCount, mFormat, mSampleCount, mWidth, mHeight, mDepth, mUsage);
  8. }
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2、CommandStream

  1. // 构造函数:
  2. CommandStream::CommandStream(Driver& driver, CircularBuffer& buffer) noexcept
  3.         : mDriver(driver),
  4.           mCurrentBuffer(buffer),
  5.           mDispatcher(driver.getDispatcher())
  6. {
  8. }
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  1. // 纹理创建函数
  2.   inline backend::TextureHandle createTexture(
  3.     backend::SamplerType target,
  4.     uint8_t levels,
  5.     backend::TextureFormat format,
  6.     uint8_t samples,
  7.     uint32_t width,
  8.     uint32_t height,
  9.     uint32_t depth,
  10.     backend::TextureUsage usage) {
  12.     // 分配结构体内存
  13.     backend::TextureHandle result = this->mDriver.createTextureS();
  15.     // 定义命令类型
  16.     using Cmd = CommandType<decltype(&Driver::createTextureR)>::Command<&Driver::createTextureR>;
  18.     // 分配命令缓冲区内存
  19.     void* const p = this->allocateCommand(CommandBase::align(sizeof(Cmd)));
  21.     // 在分配的内存上构造命令对象
  22.     new (p) Cmd(
  23.         // 真正需要执行的命令
  24.         this->mDispatcher.createTexture_,
  25.         backend::TextureHandle(result),
  26.         std::move(target),
  27.         std::move(levels),
  28.         std::move(format),
  29.         std::move(samples),
  30.         std::move(width),
  31.         std::move(height),
  32.         std::move(depth),
  33.         std::move(usage)
  34.     );
  35.     return result;
  36.   }
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3、Command

  1. // 特化模板类 Command
  2. template<>
  3. class Command<&filament::backend::Driver::createTextureR> : public filament::backend::CommandBase {
  4.     using SavedParameters = std::tuple<
  5.         std::remove_reference_t<filament::backend::Handle<filament::backend::HwTexture>>,
  6.         std::remove_reference_t<filament::backend::SamplerType>,
  7.         std::remove_reference_t<unsigned char>,
  8.         std::remove_reference_t<filament::backend::TextureFormat>,
  9.         std::remove_reference_t<unsigned char>,
  10.         std::remove_reference_t<unsigned int>,
  11.         std::remove_reference_t<unsigned int>,
  12.         std::remove_reference_t<unsigned int>,
  13.         std::remove_reference_t<filament::backend::TextureUsage>
  14.     >;
  16.     SavedParameters mArgs;
  18.     void log() noexcept;
  19.     template <std::size_t ...I>
  20.     void log(std::index_sequence<I...>) noexcept;
  22. public:
  23.     template <typename M, typename D>
  24.     static inline void execute(M &&method, D &&driver, filament::backend::CommandBase *base, intptr_t *next);
  26.     inline Command(Command<&filament::backend::Driver::createTextureR> &&rhs) noexcept = default;
  28.     template <typename ...A>
  29.     inline constexpr explicit Command(filament::backend::Execute execute, A &&...args);
  31.     template<>
  32.     inline constexpr explicit Command<filament::backend::Handle<filament::backend::HwTexture>,
  33.                                       filament::backend::SamplerType,
  34.                                       unsigned char,
  35.                                       filament::backend::TextureFormat,
  36.                                       unsigned char,
  37.                                       unsigned int,
  38.                                       unsigned int,
  39.                                       unsigned int,
  40.                                       filament::backend::TextureUsage>(
  41.         filament::backend::Execute execute,
  42.         filament::backend::Handle<filament::backend::HwTexture> &&arg1,
  43.         filament::backend::SamplerType &&arg2,
  44.         unsigned char &&arg3,
  45.         filament::backend::TextureFormat &&arg4,
  46.         unsigned char &&arg5,
  47.         unsigned int &&arg6,
  48.         unsigned int &&arg7,
  49.         unsigned int &&arg8,
  50.         filament::backend::TextureUsage &&arg9
  51.     ) : filament::backend::CommandBase(execute),
  52.         mArgs(std::forward<filament::backend::Handle<filament::backend::HwTexture>>(arg1),
  53.               std::forward<filament::backend::SamplerType>(arg2),
  54.               std::forward<unsigned char>(arg3),
  55.               std::forward<filament::backend::TextureFormat>(arg4),
  56.               std::forward<unsigned char>(arg5),
  57.               std::forward<unsigned int>(arg6),
  58.               std::forward<unsigned int>(arg7),
  59.               std::forward<unsigned int>(arg8),
  60.               std::forward<filament::backend::TextureUsage>(arg9)) {
  61.     }
  63.     static inline void *operator new(std::size_t, void *ptr) {
  64.         if (__builtin_expect(!(ptr), false)) {
  65.             utils::panic(__func__, "root/filament/filament/backend/include/private/backend/CommandStream.h", 159, "ptr");
  66.         }
  67.         return ptr;
  68.     }
  69. };
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4、Driver

1)命令的绑定

  1. Dispatcher OpenGLDriver::getDispatcher() const noexcept {
  2.     auto dispatcher = ConcreteDispatcher<OpenGLDriver>::make();
  3.     return dispatcher;
  4. }
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2)分配结构体内存

  1. struct GLTexture : public HwTexture {
  2.     using HwTexture::HwTexture;
  3.     struct GL {
  4.         GL() noexcept : imported(false), external(false), sidecarSamples(1), reserved1(0) {}
  5.         GLuint id = 0;          // texture or renderbuffer id
  6.         GLenum target = 0;
  7.         GLenum internalFormat = 0;
  8.         GLuint sidecarRenderBufferMS = 0;  // multi-sample sidecar renderbuffer
  10.         // texture parameters go here too
  11.         GLfloat anisotropy = 1.0;
  12.         int8_t baseLevel = 127;
  13.         int8_t maxLevel = -1;
  14.         uint8_t reserved0 = 0;
  15.         bool imported           : 1;
  16.         bool external           : 1;
  17.         uint8_t sidecarSamples  : 3;
  18.         uint8_t reserved1       : 3;
  19.         std::array<TextureSwizzle, 4> swizzle{
  20.                 TextureSwizzle::CHANNEL_0,
  21.                 TextureSwizzle::CHANNEL_1,
  22.                 TextureSwizzle::CHANNEL_2,
  23.                 TextureSwizzle::CHANNEL_3
  24.         };
  25.     } gl;
  26.     mutable Handle<GLTextureRef> ref;
  27.     OpenGLPlatform::ExternalTexture* externalTexture = nullptr;
  28. };
  30. // 分配内存并构造一个 filament::backend::GLTexture 对象
  31. template<> Handle<GLTexture> initHandle<filament::backend::GLTexture, <>>() {
  32.     return this->mHandleAllocator.allocateAndConstruct<filament::backend::GLTexture>();
  33. }
  35. Handle<HwTexture> OpenGLDriver::createTextureS() noexcept {
  36.     return this->initHandle<GLTexture>();
  37. }
复制代码
3)使用 OpenGL API 创建纹理

  1. void OpenGLDriver::createTextureR(Handle<HwTexture> th, SamplerType target, uint8_t levels,
  2.         TextureFormat format, uint8_t samples, uint32_t w, uint32_t h, uint32_t depth,
  3.         TextureUsage usage) {
  4.     auto &gl = this->mContext;
  5.     glTexStorage2D(t->gl.target, GLsizei(t->levels), t->gl.internalFormat, GLsizei(width), GLsizei(height));
  6.     // ...
  7. }
复制代码
5、Dispatcher

  1. using Execute = void (*)(Driver& driver, CommandBase* self, intptr_t* next);
  2. Execute createTexture_;
复制代码
  1. // 这里完成 底层驱动 绑定到 Dispatcher 上
  2. template <typename ConcreteDriver> class ConcreteDispatcher {
  3.     static void createTexture(Driver &driver, CommandBase *base, intptr_t *next) {
  4.         using Cmd = CommandType<decltype(&Driver::createTextureR)>::Command<&Driver::createTextureR>;
  5.         ConcreteDriver &concreteDriver = static_cast<ConcreteDriver &>(driver);
  6.         Cmd::execute(& ConcreteDriver::createTextureR, concreteDriver, base, next);
  7.     }
  8. }
  9. template <typename ConcreteDriver> Dispatcher ConcreteDispatcher<ConcreteDriver>::make() {
  10.     Dispatcher dispatcher;
  11.     dispatcher.createTexture_ = &ConcreteDispatcher<T>::createTexture;
  12.     // ...
  13.     return dispatcher;
  14. }
复制代码
四、总结

这表明 Engine -> CommandStream -> Dispatcher 形成了调用链，每一层都负责不同的任务，Engine 负责 API 层接口，CommandStream 负责命令封装，Dispatcher 负责命令派发, Driver 负责最终执行。
五、辅助工具

1)Engine

命令出处：
   cmake-build-debug/compile_commands.json
  预处置惩罚命令:
  1. // root/filament:
  2. clang++ -E \
  3. -I../libs/filabridge/include \
  4. -I../third_party/robin-map \
  5. -I../libs/utils/include \
  6. -I../libs/filaflat/include \
  7. -I../libs/math/include \
  8. -I../cmake-build-debug/filament/ \
  9. -I./include \
  10. -I./backend/include \
  11. -I./src/details \
  12. -I./components \
  13. -I./src \
  14. ./src/details/Engine.cpp -o 123.cpp
复制代码
编译模板睁开:
  1. // root/filament:
  2. clang++ \
  3. -Xclang -ast-print -fsyntax-only -std=c++17 \
  4. root/filament/filament/src/Engine.cpp > record_layouts.txt 2>&1 \
  5. -Iroot/filament/filament/include \
  6. -Iroot/filament/cmake-build-debug/filament \
  7. -Iroot/filament/filament/src \
  8. -Iroot/filament/filament/backend/include \
  9. -Iroot/filament/libs/math/include \
  10. -Iroot/filament/libs/utils/include \
  11. -Iroot/filament/third_party/robin-map/tnt/.. \
  12. -Iroot/filament/libs/bluevk/include \
  13. -Iroot/filament/third_party/vkmemalloc/tnt/../include \
  14. -Iroot/filament/third_party/smol-v/tnt/../source \
  15. -Iroot/filament/libs/filaflat/include \
  16. -Iroot/filament/libs/filabridge/include \
  17. -Iroot/filament/libs/ibl/include \
  18. -Iroot/filament/libs/matdbg/include \
  19. -Iroot/filament/third_party/civetweb/tnt/../include \
  20. -Iroot/filament/libs/filamat/include \
  21. -Iroot/filament/cmake-build-debug/shaders \
  22. -Iroot/filament/cmake-build-debug/include \
  23. -Iroot/filament/third_party/glslang/glslang/tnt/../Include \
  24. -Iroot/filament/third_party/glslang/glslang/tnt/../Public \
  25. -Iroot/filament/third_party/glslang/glslang/tnt/../MachineIndependent \
  26. -Iroot/filament/third_party/glslang/glslang/tnt/../.. \
  27. -Iroot/filament/third_party/glslang/SPIRV/tnt/.. \
  28. -Iroot/filament/third_party/glslang/SPIRV/tnt/../.. \
  29. -Iroot/filament/third_party/spirv-tools/include \
  30. -Iroot/filament/third_party/spirv-headers/include \
  31. -Iroot/filament/third_party/spirv-cross/tnt/..
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2)CommandStream

预处置惩罚命令:
  1. // root/filament/backend:
  2. g++ -E -I../../libs/utils/include -I../../libs/math/include -I../include -I./include  ./src/CommandStream.cpp -o CommandStream.i
复制代码
3)Driver

  1. clang++ \
  2. -Xclang -ast-print -fsyntax-only -std=c++17 \
  3. root/filament/backend/src/opengl/OpenGLDriver.cpp > record_layouts.txt 2>&1 \
  4. -Iroot/filament/include \
  5. -Iroot/cmake-build-debug/filament \
  6. -Iroot/filament/src \
  7. -Iroot/filament/backend/include \
  8. -Iroot/filament/backend/src \
  9. -Iroot/cmake-build-debug/filament/backend \
  10. -Iroot/libs/math/include \
  11. -Iroot/libs/utils/include \
  12. -Iroot/third_party/robin-map/tnt/.. \
  13. -Iroot/libs/bluegl/include \
  14. -Iroot/libs/bluevk/include \
  15. -Iroot/third_party/vkmemalloc/tnt/../include \
  16. -Iroot/third_party/smol-v/tnt/../source \
  17. -Iroot/third_party/spirv-headers/include
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