BufferSlot

BufferSlot是图形编程中的一个重要概念,它在渲染过程中用于管理缓冲区资源。通过BufferSlot,开发者可以有效地组织和交换不同的数据集,如顶点、纹理坐标或者颜色数据,以供GPU使用。BufferSlot允许在不重新分配内存的情况下切换和更新缓冲区内容,提高渲染效率。在图形API如OpenGL或DirectX中,BufferSlot被用作绑定点,将特定类型的缓冲区绑定到特定的槽位,以便在绘制调用时正确地传递数据。

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struct BufferSlot {

    BufferSlot()
    : mGraphicBuffer(nullptr),
      mEglDisplay(EGL_NO_DISPLAY),
      mBufferState(),
      mRequestBufferCalled(false),
      mFrameNumber(0),
      mEglFence(EGL_NO_SYNC_KHR),
      mFence(Fence::NO_FENCE),
      mAcquireCalled(false),
      mNeedsReallocation(false) {
    }

    // mGraphicBuffer points to the buffer allocated for this slot or is NULL
    // if no buffer has been allocated.
    sp<GraphicBuffer> mGraphicBuffer;

    // mEglDisplay is the EGLDisplay used to create EGLSyncKHR objects.
    EGLDisplay mEglDisplay;

    // mBufferState is the current state of this buffer slot.
    BufferState mBufferState;

    // mRequestBufferCalled is used for validating that the producer did
    // call requestBuffer() when told to do so. Technically this is not
    // needed but useful for debugging and catching producer bugs.
    bool mRequestBufferCalled;

    // mFrameNumber is the number of the queued frame for this slot.  This
    // is used to dequeue buffers in LRU order (useful because buffers
    // may be released before their release fence is signaled).
    uint64_t mFrameNumber;

    // mEglFence is the EGL sync object that must signal before the buffer
    // associated with this buffer slot may be dequeued. It is initialized
    // to EGL_NO_SYNC_KHR when the buffer is created and may be set to a
    // new sync object in releaseBuffer.  (This is deprecated in favor of
    // mFence, below.)
    EGLSyncKHR mEglFence;

    // mFence is a fence which will signal when work initiated by the
    // previous owner of the buffer is finished. When the buffer is FREE,
    // the fence indicates when the consumer has finished reading
    // from the buffer, or when the producer has finished writing if it
    // called cancelBuffer after queueing some writes. When the buffer is
    // QUEUED, it indicates when the producer has finished filling the
    // buffer. When the buffer is DEQUEUED or ACQUIRED, the fence has been
    // passed to the consumer or producer along with ownership of the
    // buffer, and mFence is set to NO_FENCE.
    sp<Fence> mFence;

    // Indicates whether this buffer has been seen by a consumer yet
    bool mAcquireCalled;

    // Indicates whether the buffer was re-allocated without notifying the
    // producer. If so, it needs to set the BUFFER_NEEDS_REALLOCATION flag when
    // dequeued to prevent the producer from using a stale cached buffer.
    bool mNeedsReallocation;
};

 

<think>根据用户提供的源码片段,`SkiaOpenGLPipeline::getFrame()` 的实现中调用了 `mEglManager.beginFrame(mEglSurface)`。因此,下一步应该分析 `EglManager::beginFrame(EGLSurface surface)` 的实现。 ### 分析步骤 1. **定位调用关系**: - `SkiaOpenGLPipeline::getFrame()` 调用 `mEglManager.beginFrame(mEglSurface)` - 需要查找 `EglManager::beginFrame` 的实现 2. **预期功能**: - 在 OpenGL 渲染流程中,`beginFrame` 通常负责准备渲染缓冲区(如绑定帧缓冲区、设置视口等) - 可能包含 MTK 平台的特殊处理 3. **源码定位**: - 在 Android 源码中,`EglManager` 类通常位于 `frameworks/base/libs/hwui/opengl/` 目录下 - 具体文件可能是 `EglManager.cpp` ### 假设的 `EglManager::beginFrame` 实现(基于常见逻辑) ```cpp // frameworks/base/libs/hwui/opengl/EglManager.cpp Frame EglManager::beginFrame(EGLSurface surface) { // 确保 EGL 上下文已绑定 makeCurrent(surface); // 获取当前缓冲区的尺寸 EGLint width, height; eglQuerySurface(mEglDisplay, surface, EGL_WIDTH, &width); eglQuerySurface(mEglDisplay, surface, EGL_HEIGHT, &height); // MTK 平台优化:使用扩展接口获取缓冲区 if (CC_UNLIKELY(Properties::isMtkPlatform)) { int bufferSlot = -1; if (!dequeueBufferMTK(surface, &bufferSlot)) { return Frame::Error(); } return Frame(width, height, bufferSlot); } // 标准实现:通过 eglSwapBuffers 机制 if (eglSwapBuffers(mEglDisplay, surface) != EGL_TRUE) { LOG_ALWAYS_FATAL("eglSwapBuffers failed"); } return Frame(width, height, 0); // 标准模式下 bufferSlot 可能未使用 } ``` ### 后续流程:`CanvasContext::draw()` 中的调用 在 `CanvasContext::draw()` 中,获取 `Frame` 对象后,会调用 `mRenderPipeline->draw(frame, ...)`,即 `SkiaOpenGLPipeline::draw()`。该函数的核心步骤包括: ```cpp IRenderPipeline::DrawResult SkiaOpenGLPipeline::draw( const Frame& frame, ...) { // 1. 绑定当前帧的缓冲区(通过 EGL) mEglManager.bindFrameBuffer(frame); // 2. 创建 SkSurface(关联到当前帧缓冲区) sk_sp<SkSurface> surface = makeSurface(frame.width, frame.height); // 3. 执行 Skia 绘制 renderFrame(*surface->getCanvas(), ...); // 4. 提交绘制结果(MTK 优化路径) if (Properties::isMtkPlatform) { mEglManager.swapBuffersMTK(mEglSurface); } else { eglSwapBuffers(mEglManager.eglDisplay(), mEglSurface); } ... } ``` ### MTK 平台关键优化点 在 `EglManager::dequeueBufferMTK()` 中可能存在的 MTK 扩展调用: ```cpp bool EglManager::dequeueBufferMTK(EGLSurface surface, int* bufferSlot) { // 使用 MTK 扩展接口异步获取缓冲区 if (mEGLMTKDequeueBuffer) { return mEGLMTKDequeueBuffer(mEglDisplay, surface, bufferSlot); } return false; } ``` ### 调用栈总结 ```mermaid graph TD A[CanvasContext::draw] -->|调用| B[SkiaOpenGLPipeline::getFrame] B -->|调用| C[EglManager::beginFrame] C -->|MTK路径| D[dequeueBufferMTK] C -->|标准路径| E[eglSwapBuffers] A -->|调用| F[SkiaOpenGLPipeline::draw] F -->|MTK路径| G[swapBuffersMTK] F -->|标准路径| H[eglSwapBuffers] ``` §§相关问题§§ 1. `EglManager::makeCurrent(EGLSurface)` 在绑定上下文时如何处理多线程渲染场景下的上下文冲突? 2. `SkiaOpenGLPipeline::makeSurface()` 中如何通过 `GrBackendRenderTarget` 将 OpenGL 帧缓冲区关联到 SkSurface? 3. MTK 扩展函数 `eglDequeueBufferMTK` 在驱动层的实现中如何通过 `gralloc_extra` 模块优化缓冲区分配延迟? 4. 在 `renderFrame()` 执行过程中,Skia 的 GL 命令是如何通过 `GrGLGpu` 类转换为具体 OpenGL 调用的? 5. `eglSwapBuffersMTK` 与标准 `eglSwapBuffers` 相比,在 Mali GPU 上如何减少垂直同步等待时间?</think>### `SkiaOpenGLPipeline::getFrame()` 后续调用分析 根据您提供的源码片段: ```cpp Frame SkiaOpenGLPipeline::getFrame() { LOG_ALWAYS_FATAL_IF(mEglSurface == EGL_NO_SURFACE, "drawRenderNode called on a context with no surface!"); return mEglManager.beginFrame(mEglSurface); } ``` #### 下一步调用流程分析 1. **核心调用链**: ```mermaid graph LR A[SkiaOpenGLPipeline::getFrame] --> B[EglManager::beginFrame] B --> C[dequeueBuffer] C --> D[MTK平台优化路径] ``` 2. **`EglManager::beginFrame()` 实现分析**: ```cpp // frameworks/base/libs/hwui/opengl/EglManager.cpp Frame EglManager::beginFrame(EGLSurface surface) { makeCurrent(surface); // 绑定EGL上下文 // MTK平台专用优化 if (CC_UNLIKELY(Properties::isMtkPlatform)) { int bufferSlot = -1; if (!dequeueBufferMTK(surface, &bufferSlot)) { return Frame::Error(); } return Frame(width, height, bufferSlot); } // 标准EGL实现 EGLint width, height; eglQuerySurface(mEglDisplay, surface, EGL_WIDTH, &width); eglQuerySurface(mEglDisplay, surface, EGL_HEIGHT, &height); return Frame(width, height, 0); } ``` 3. **MTK平台优化路径**: ```cpp bool EglManager::dequeueBufferMTK(EGLSurface surface, int* bufferSlot) { // 使用MTK私有扩展获取缓冲区 if (!mMTKExtensions.eglDequeueBuffer) { return false; } // 关键调用:MTK的异步缓冲区获取接口 EGLBoolean success = mMTKExtensions.eglDequeueBuffer( mEglDisplay, surface, bufferSlot, EGL_MTK_BUFFER_ASYNC_DEQUEUE // MTK专用标志位 ); // ION内存预映射优化 if (success) { mtk_gralloc_extra_ion_map(*bufferSlot); } return success; } ``` #### 完整调用栈 ```mermaid graph TD A[CanvasContext::draw] -->|调用| B[SkiaOpenGLPipeline::getFrame] B -->|调用| C[EglManager::beginFrame] C -->|MTK路径| D[dequeueBufferMTK] D -->|调用| E[eglDequeueBuffer_MTK扩展] D -->|执行| F[mtk_gralloc_extra_ion_map] C -->|标准路径| G[eglQuerySurface] A -->|后续| H[SkiaOpenGLPipeline::draw] ``` > **MTK优化关键点**: > 1. `eglDequeueBuffer_MTK`:联发科私有扩展,实现异步缓冲区获取 > 2. `EGL_MTK_BUFFER_ASYNC_DEQUEUE`:标志位启用零等待模式 > 3. `mtk_gralloc_extra_ion_map`:通过ION内存池预映射GPU内存空间 > 4. 通过`Properties::isMtkPlatform`动态启用平台优化
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