Android SurfaceFlinger中的Layer,LayerDim,LayerBlur,LayerBuffer

http://blog.csdn.net/DroidPhone/archive/2010/11/11/6002237.aspx

应用程序中不同类型的Surface,在FrameWorks本地层的SurfaceFlinger中，分别对应着不同的Layer类，本文主要是讨论这几种Layer的实现和差异。

阅读本文之前，最好对SurfaceFlinger这个系统服务有所了解，可以参阅我的以下两篇文章：

• Android SurfaceFlinger中的SharedClient -- 客户端（Surface）和服务端（Layer）之间的显示缓冲区管理
• Android SurfaceFlinger中的工作线程：threadLoop()

视觉效果

下面几张图片分别表示了不同Layer产生的视觉效果：

• Layer对应普通的窗口
• LayerDim 会使他后面的窗口产生一个变暗的透明效果
• LayerBlur在LayerDim的基础上，背景会产生模糊的效果

创建Layer

默认地，创建普通的窗口Surface，在SurfaceFlinger中会创建Layer类，如果想创建LayerDim或LayerBlur，应用程序需要在绑定View之前设置一下窗口的标志位：

创建LayerDim效果：

 

@Override
protected void onCreate(Bundle icicle) {
    // Be sure to call the super class.
    super.onCreate(icicle);

    // Have the system blur any windows behind this one.
    getWindow().setFlags(WindowManager.LayoutParams.FLAG_DIM_BEHIND,
            WindowManager.LayoutParams.FLAG_DIM_BEHIND);
    ......
    setContentView(......);
}

@Override protected void onCreate(Bundle icicle) { // Be sure to call the super class. super.onCreate(icicle); // Have the system blur any windows behind this one. getWindow().setFlags(WindowManager.LayoutParams.FLAG_DIM_BEHIND, WindowManager.LayoutParams.FLAG_DIM_BEHIND); ...... setContentView(......); }

 

创建LayerBlur效果：

 

@Override
protected void onCreate(Bundle icicle) {
    // Be sure to call the super class.
    super.onCreate(icicle);

    // Have the system blur any windows behind this one.
    getWindow().setFlags(WindowManager.LayoutParams.FLAG_BLUR_BEHIND,
            WindowManager.LayoutParams.FLAG_BLUR_BEHIND);
    ......
    setContentView(......);
}

@Override protected void onCreate(Bundle icicle) { // Be sure to call the super class. super.onCreate(icicle); // Have the system blur any windows behind this one. getWindow().setFlags(WindowManager.LayoutParams.FLAG_BLUR_BEHIND, WindowManager.LayoutParams.FLAG_BLUR_BEHIND); ...... setContentView(......); }

 

相应地，在SufaceFlinger中，会根据Java层传入的标志，创建不同的Layer:

 

sp<ISurface> SurfaceFlinger::createSurface(ClientID clientId, int pid,
        const String8& name, ISurfaceFlingerClient::surface_data_t* params,
        DisplayID d, uint32_t w, uint32_t h, PixelFormat format,
        uint32_t flags)
{
    sp<LayerBaseClient> layer;
    sp<LayerBaseClient::Surface> surfaceHandle;
    ......
    switch (flags & eFXSurfaceMask) {
        case eFXSurfaceNormal:
            if (UNLIKELY(flags & ePushBuffers)) {
                layer = createPushBuffersSurfaceLocked(client, d, id,
                        w, h, flags);
            } else {
                layer = createNormalSurfaceLocked(client, d, id,
                        w, h, flags, format);
            }
            break;
        case eFXSurfaceBlur:
            layer = createBlurSurfaceLocked(client, d, id, w, h, flags);
            break;
        case eFXSurfaceDim:
            layer = createDimSurfaceLocked(client, d, id, w, h, flags);
            break;
    }

    if (layer != 0) {
        layer->setName(name);
        setTransactionFlags(eTransactionNeeded);
        surfaceHandle = layer->getSurface();
        ........
    }

    return surfaceHandle;
}

sp<ISurface> SurfaceFlinger::createSurface(ClientID clientId, int pid, const String8& name, ISurfaceFlingerClient::surface_data_t* params, DisplayID d, uint32_t w, uint32_t h, PixelFormat format, uint32_t flags) { sp<LayerBaseClient> layer; sp<LayerBaseClient::Surface> surfaceHandle; ...... switch (flags & eFXSurfaceMask) { case eFXSurfaceNormal: if (UNLIKELY(flags & ePushBuffers)) { layer = createPushBuffersSurfaceLocked(client, d, id, w, h, flags); } else { layer = createNormalSurfaceLocked(client, d, id, w, h, flags, format); } break; case eFXSurfaceBlur: layer = createBlurSurfaceLocked(client, d, id, w, h, flags); break; case eFXSurfaceDim: layer = createDimSurfaceLocked(client, d, id, w, h, flags); break; } if (layer != 0) { layer->setName(name); setTransactionFlags(eTransactionNeeded); surfaceHandle = layer->getSurface(); ........ } return surfaceHandle; }

 

Layer类的静态结构

下面的图展示了Layer类之间的继承关系：

• 所有的Layer都继承了LayerBaseClient，SurfaceFlinger统一通过LayerBaseClient类访问其他的派生Layer类
• LayerBaseClient的内嵌类Surface继承了ISurface接口，ISurface用于和SurfaceFlinger的客户端交互
• Layer和LayerBuffer都有各自的内嵌类：SurfaceLayer、SurfaceLayerBuffer，继承了LayerBaseClient的内嵌类Surface
•  LayerBuffer还有另外的内嵌类：Source，并且派生出另外两个内嵌类：BufferSource、OverlaySource

ISurface接口

 ISurface接口其实非常简单，只有几个函数：

• requestBuffer()        // Layer类使用，用于申请frontbuffer、backbuffer，初始化或size变化时调用
• registerBuffers()      // LayerBuffer类使用，用于注册IMemoryHeap接口
• unregisterBuffers()  // LayerBuffer类使用，用于注销IMemoryHeap接口
• postBuffer()             // post用于刷新的图像数据
• createOverlay()       // 用于创建Overlay表面

LayerBaseClient的派生类中，会有一个内嵌类，继承LayerBaseClient::Surface，然后根据需要会实现该接口的相应函数。

Layer类

Layer类是使用最多的一个，普通的应用程序窗口都会对应一个Layer类，Layer类的内嵌类SurfaceLayer继承了ISurface接口，创建Layer类时，将会返回一个ISurface接口给创建者。并且，Layer类在创建时会建立两个GraphicBuffer对象，这两个Buffer在不同的时刻分别被作为frontbuffer和backbuffer，frontbuffer用于本窗口的画图操作，backbuffer用于所有窗口的混合操作。但是两个GraphicBuffer对象在创建时并没有真正地分配内存，而是在第一次lockBuffer时才正式通过ISurface接口的requestBuffer方法申请内存，当窗口的大小发生变化时，也要重新分配适合窗口大小的内存。Layer类的主要成员函数如下：

• createSurface()  返回ISurface接口
• setBuffers()  创建两个GraphicBuffer对象，创建ISurface接口的实现类SurfaceLayer
• onDraw()  把frontbuffer中的图像数据通过OpenGL混合到OpenGL的主表面中
• doTransaction()  检测并处理窗口大小变化
• lockPageFlip()  获取frontbuffer，并且生成frontbuffer的OpenGL贴图
• finishPageFlip()  unlock frontbuffer，此后该buffer会queue到空闲列表中，下次可以作为backbuffer使用

LayerDim和LayerBlur

LayerDim和LayerBlur，他们的显示内容是固定不变的（透明的黑色），所以不需要分配两个GraphicBuffer对象，因此它们也没有继承自LayerBaseClient::Surface的内嵌类，而是直接使用LayerBaseClient::Surface类作为它们的ISurface接口。以LayerDim为例跟踪一下它的Draw过程：

• 创建LayerDim时，在LayerDim.initDimmer()中生成纯黑的OpenGL贴图

 

void LayerDim::initDimmer(SurfaceFlinger* flinger, uint32_t w, uint32_t h)
{
    sTexId = -1;
    sImage = EGL_NO_IMAGE_KHR;
    ......
    if (LIKELY(flags & DisplayHardware::DIRECT_TEXTURE)) {
        /* 申请GraphicBuffer */
        sp<GraphicBuffer> buffer = new GraphicBuffer(w, h, PIXEL_FORMAT_RGB_565,
                 GraphicBuffer::USAGE_SW_WRITE_OFTEN |
                 GraphicBuffer::USAGE_HW_TEXTURE);

        android_native_buffer_t* clientBuf = buffer->getNativeBuffer();
       /* 申请OpenGL贴图 */
        glGenTextures(1, &sTexId);
        glBindTexture(GL_TEXTURE_2D, sTexId);

        EGLDisplay dpy = eglGetCurrentDisplay();
        sImage = eglCreateImageKHR(dpy, EGL_NO_CONTEXT,
                EGL_NATIVE_BUFFER_ANDROID, (EGLClientBuffer)clientBuf, 0);
        glEGLImageTargetTexture2DOES(GL_TEXTURE_2D, (GLeglImageOES)sImage);
        ......
        // initialize the texture with zeros
        GGLSurface t;
        buffer->lock(&t, GRALLOC_USAGE_SW_WRITE_OFTEN);
        memset(t.data, 0, t.stride * t.height * 2);
        buffer->unlock();
        sUseTexture = true;
    }
}

void LayerDim::initDimmer(SurfaceFlinger* flinger, uint32_t w, uint32_t h) { sTexId = -1; sImage = EGL_NO_IMAGE_KHR; ...... if (LIKELY(flags & DisplayHardware::DIRECT_TEXTURE)) { /* 申请GraphicBuffer */ sp<GraphicBuffer> buffer = new GraphicBuffer(w, h, PIXEL_FORMAT_RGB_565, GraphicBuffer::USAGE_SW_WRITE_OFTEN | GraphicBuffer::USAGE_HW_TEXTURE); android_native_buffer_t* clientBuf = buffer->getNativeBuffer(); /* 申请OpenGL贴图 */ glGenTextures(1, &sTexId); glBindTexture(GL_TEXTURE_2D, sTexId); EGLDisplay dpy = eglGetCurrentDisplay(); sImage = eglCreateImageKHR(dpy, EGL_NO_CONTEXT, EGL_NATIVE_BUFFER_ANDROID, (EGLClientBuffer)clientBuf, 0); glEGLImageTargetTexture2DOES(GL_TEXTURE_2D, (GLeglImageOES)sImage); ...... // initialize the texture with zeros GGLSurface t; buffer->lock(&t, GRALLOC_USAGE_SW_WRITE_OFTEN); memset(t.data, 0, t.stride * t.height * 2); buffer->unlock(); sUseTexture = true; } }

 

• 在OnDraw()中把第一步生成的贴图混合到OpenGL的主表面中

 

void LayerDim::onDraw(const Region& clip) const
{
    const State& s(drawingState());
    Region::const_iterator it = clip.begin();
    Region::const_iterator const end = clip.end();
    if (s.alpha>0 && (it != end)) {
        const DisplayHardware& hw(graphicPlane(0).displayHardware());
        ......
        /* 设置透明值 */
        glColor4x(0, 0, 0, alpha);

#if defined(DIM_WITH_TEXTURE) && defined(EGL_ANDROID_image_native_buffer)
        if (sUseTexture) {
            glBindTexture(GL_TEXTURE_2D, sTexId);
            glEnable(GL_TEXTURE_2D);
            glTexEnvx(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);
            const GLshort texCoords[4][2] = {
                    { 0,  0 },
                    { 0,  1 },
                    { 1,  1 },
                    { 1,  0 }
            };
            glMatrixMode(GL_TEXTURE);
            glLoadIdentity();
            glEnableClientState(GL_TEXTURE_COORD_ARRAY);
            glTexCoordPointer(2, GL_SHORT, 0, texCoords);
        } else
#endif
        {
            glDisable(GL_TEXTURE_2D);
        }

        GLshort w = sWidth;
        GLshort h = sHeight;
        const GLshort vertices[4][2] = {
                { 0, 0 },
                { 0, h },
                { w, h },
                { w, 0 }
        };
        glVertexPointer(2, GL_SHORT, 0, vertices);

        while (it != end) {
            const Rect& r = *it++;
            const GLint sy = fbHeight - (r.top + r.height());
            glScissor(r.left, sy, r.width(), r.height());
            glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
        }
    }
    glDisableClientState(GL_TEXTURE_COORD_ARRAY);
}

void LayerDim::onDraw(const Region& clip) const { const State& s(drawingState()); Region::const_iterator it = clip.begin(); Region::const_iterator const end = clip.end(); if (s.alpha>0 && (it != end)) { const DisplayHardware& hw(graphicPlane(0).displayHardware()); ...... /* 设置透明值 */ glColor4x(0, 0, 0, alpha); #if defined(DIM_WITH_TEXTURE) && defined(EGL_ANDROID_image_native_buffer) if (sUseTexture) { glBindTexture(GL_TEXTURE_2D, sTexId); glEnable(GL_TEXTURE_2D); glTexEnvx(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE); const GLshort texCoords[4][2] = { { 0, 0 }, { 0, 1 }, { 1, 1 }, { 1, 0 } }; glMatrixMode(GL_TEXTURE); glLoadIdentity(); glEnableClientState(GL_TEXTURE_COORD_ARRAY); glTexCoordPointer(2, GL_SHORT, 0, texCoords); } else #endif { glDisable(GL_TEXTURE_2D); } GLshort w = sWidth; GLshort h = sHeight; const GLshort vertices[4][2] = { { 0, 0 }, { 0, h }, { w, h }, { w, 0 } }; glVertexPointer(2, GL_SHORT, 0, vertices); while (it != end) { const Rect& r = *it++; const GLint sy = fbHeight - (r.top + r.height()); glScissor(r.left, sy, r.width(), r.height()); glDrawArrays(GL_TRIANGLE_FAN, 0, 4); } } glDisableClientState(GL_TEXTURE_COORD_ARRAY); }

 

 

 

LayerBuffer

《未完待续》