概览

Android 中有多个窗口，每个窗口都是一个 Renderer，每个窗口渲染后把 buffer 传递给 Composer。由 Composer 来合成每个窗口的 buffer，最后发送给显示器显示。

Graphic data flow through Android

Renderer 和 Composer 通过 BufferQueue 交互，它是一个生产者消费者模式，Renderer 是生产者，Composer 是消费者。

BufferQueue communication process

• 生产者从 BufferQueue dequeue 一个 buffer，填充数据后通过 queue 把 buffer 还给 BufferQueue。
• 消费者从 BufferQueue acquire 一个 buffer，合成并送显完成后，通过 release 把 buffer 还给 BufferQueue。

该文档介绍 BufferQueue 如何管理 Buffer。

BufferQueue

commit 289ade165e60b5f71734d30e535f16eb1f4313ad
Author: Dan Stoza <[email protected]>
Date:   Fri Feb 28 11:17:17 2014 -0800

    Split BufferQueue into core + producer + consumer

    Change-Id: Idc39f1e511d68ce4f02202d35425a419bc0bcd92

 include/gui/BufferItem.h          | 103 +++++++++++++++++
 include/gui/BufferQueueConsumer.h | 148 ++++++++++++++++++++++++
 include/gui/BufferQueueCore.h     | 120 ++++++++++++++++++++
 include/gui/BufferQueueProducer.h | 165 +++++++++++++++++++++++++++
 include/gui/BufferSlot.h          | 136 ++++++++++++++++++++++
 libs/gui/Android.mk               |   5 +
 libs/gui/BufferItem.cpp           | 190 +++++++++++++++++++++++++++++++
 libs/gui/BufferQueueConsumer.cpp  | 398 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 libs/gui/BufferQueueCore.cpp      | 209 ++++++++++++++++++++++++++++++++++
 libs/gui/BufferQueueProducer.cpp  | 705 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 libs/gui/BufferSlot.cpp           |  15 +++
 11 files changed, 2194 insertions(+)

2014 年，Google 把 BufferQueue 拆分成了 BufferQueueCore、BufferQueueProducer 和 BufferQueueConsumer。

BufferQueueCore 管理 BufferSlot，它有一个成员 BufferQueueDefs::SlotsType，它是 BufferSlot 数组，BufferSlot 有成员 sp<GraphicBuffer>。BufferQueueProducer 和 BufferQueueConsumer 中有 BufferQueueDefs::SlotsType 引用，通过引用可以访问 BufferSlot。

typedef BufferSlot SlotsType[NUM_BUFFER_SLOTS];
BufferQueueDefs::SlotsType mSlots;

struct BufferSlot {
    sp<GraphicBuffer> mGraphicBuffer;
    BufferState mBufferState;
}

BufferSlot

BufferSlot，顾名思义是 buffer 插槽，它有成员 BufferState 和 sp<GraphicBuffer>。生产者和消费者获取 BufferSlot 并改变其状态。