简介： CSDN博客专家，专注Android/Linux系统，分享多mic语音方案、音视频、编解码等技术，与大家一起成长！

优质专栏：Audio工程师进阶系列【原创干货持续更新中……】🚀

人生格言： 人生从来没有捷径，只有行动才是治疗恐惧和懒惰的唯一良药.

更多原创,欢迎关注：Android系统攻城狮

1.前言

本篇目的：Android图形系统中，HWC特别的复杂，特别是HWComposer、ComposerImpl、Composer、Hwc2::Composer之间的关系，有种剪不断理还乱的感觉，通过几个演化例子，看清楚它本来的面目。

2.HWComposer、ComposerImpl、Composer、Hwc2::Composer定义与实现

1.HWComposer实现

frameworks/native/services/surfaceflinger/DisplayHardware/HWComposer.h

<1>.android::HWComposer定义

namespace Hwc2 {
   
class Composer;
}

namespace android {
   
class HWComposer {
   
	virtual ~HWComposer();
    virtual void setCallback(HWC2::ComposerCallback*) = 0;
    ....
};
}

<2>.impl::HWComposer定义(继承自android::HWComposer)

namespace impl {
   

class HWComposer final : public android::HWComposer {
   
public:
    explicit HWComposer(std::unique_ptr<Hwc2::Composer> composer);
    explicit HWComposer(const std::string& composerServiceName);

    ~HWComposer() override;
};
}

<3>.impl::HWComposer实现

frameworks/native/services/surfaceflinger/DisplayHardware/HWComposer.cpp

namespace impl {
   
	HWComposer::HWComposer(std::unique_ptr<Hwc2::Composer> composer)
      : mComposer(std::move(composer)),
        mMaxVirtualDisplayDimension(static_cast<size_t>(sysprop::max_virtual_display_dimension(0))),
        mUpdateDeviceProductInfoOnHotplugReconnect(
                sysprop::update_device_product_info_on_hotplug_reconnect(false)) {
   }

HWComposer::HWComposer(const std::string& composerServiceName)
      : HWComposer(std::make_unique<Hwc2::impl::Composer>(composerServiceName)) {
   }

HWComposer::~HWComposer() {
   
    mDisplayData.clear();
}
}

HWComposer构造函数通过它的委托构造函数，通过std::make_uniqueHwc2::impl::Composer(composerServiceName)实例画，那么Hwc2::impl::Composer的实现在哪呢？

2.ComposerImpl实现（Hwc2::Composer是它的别名）

hardware/interfaces/graphics/composer/2.1/utils/hal/include/composer-hal/2.1/Composer.h

<1>.Composer定义，它是ComposerImpl的别名

using Composer = detail::ComposerImpl<IComposer, ComposerHal>;
template <typename Interface, typename Hal>
class ComposerImpl : public Interface {
   
   public:
    static std::unique_ptr<ComposerImpl> create(std::unique_ptr<Hal> hal) {