DDMS和豌豆荚 ScreenCapture流程

chipset: MSM8x25Q

codebase:  Android4.1

Screencap和screenshot大同小异，不过前者是直接用build好的一个可执行文件来操作的，文件位于/system/bin/screencap。看下code:

int main(int argc, char** argv)
{
    const char* pname = argv[0];
    bool png = false;
    int c;
    while ((c = getopt(argc, argv, "ph")) != -1) {
        switch (c) {
            case 'p':
                png = true;
                break;
            case '?':
            case 'h':
                usage(pname);
                return 1;
        }
    }
    argc -= optind;
    argv += optind;

    int fd = -1;
    if (argc == 0) {
        fd = dup(STDOUT_FILENO);
} else if (argc == 1) {
		/*获取参数argv[0]，为要保存screencap的path*/
        const char* fn = argv[0];
        fd = open(fn, O_WRONLY | O_CREAT | O_TRUNC, 0664);
        if (fd == -1) {
            fprintf(stderr, "Error opening file: %s (%s)\n", fn, strerror(errno));
            return 1;
        }
        const int len = strlen(fn);
		/*path file是否为png*/
        if (len >= 4 && 0 == strcmp(fn+len-4, ".png")) {
            png = true;
        }
    }
    
    if (fd == -1) {
        usage(pname);
        return 1;
    }

    void const* mapbase = MAP_FAILED;
    ssize_t mapsize = -1;

    void const* base = 0;
    uint32_t w, h, f;
    size_t size = 0;
ScreenshotClient screenshot;
/*最终通过SF的update去重画*/
if (screenshot.update() == NO_ERROR) {
		/*获得显示buffer的address*/
        base = screenshot.getPixels();
        w = screenshot.getWidth();
        h = screenshot.getHeight();
        f = screenshot.getFormat();
        size = screenshot.getSize();
        ALOGE("screencap w:%d, h:%d, f:%d, size:%d", w, h, f, size);
} else {
		/*上面用SF更新buffer失败的话就直接从fb中获得。*/
        const char* fbpath = "/dev/graphics/fb0";
        int fb = open(fbpath, O_RDONLY);
        if (fb >= 0) {
            struct fb_var_screeninfo vinfo;
            if (ioctl(fb, FBIOGET_VSCREENINFO, &vinfo) == 0) {
                uint32_t bytespp;
                if (vinfoToPixelFormat(vinfo, &bytespp, &f) == NO_ERROR) {
                    size_t offset = (vinfo.xoffset + vinfo.yoffset*(((vinfo.xres + 31) >> 5) << 5)) * bytespp;
                    w = ((vinfo.xres + 31) >> 5) << 5;
                    h = vinfo.yres;
                    size = w*h*bytespp;
                    ALOGE("screencap offset:%d, w:%d, h:%d, size:%d", offset, w, h, size);
                    mapsize = offset + size;
                    mapbase = mmap(0, mapsize, PROT_READ, MAP_PRIVATE, fb, 0);
                    if (mapbase != MAP_FAILED) {
                        base = (void const *)((char const *)mapbase + offset);
                    }
                }
            }
            close(fb);
        }
    }

if (base) {
	/*如果是png格式就需要压缩、编码*/
        if (png) {
            SkBitmap b;
            b.setConfig(flinger2skia(f), w, h);
            b.setPixels((void*)base);
            SkDynamicMemoryWStream stream;
            SkImageEncoder::EncodeStream(&stream, b,
                    SkImageEncoder::kPNG_Type, SkImageEncoder::kDefaultQuality);
            SkData* streamData = stream.copyToData();
            write(fd, streamData->data(), streamData->size());
            streamData->unref();
        } else {
		/*将宽、高，数据格式以及显示数据写到fd中*/
            write(fd, &w, 4);
            write(fd, &h, 4);
            write(fd, &f, 4);
            write(fd, base, size);
        }
    }
    close(fd);
    if (mapbase != MAP_FAILED) {
        munmap((void *)mapbase, mapsize);
    }
    return 0;
}

整个流程比较简单，不过要注意从fb中直接获取，对于当camera preview或者video playback

的数据时YUV的情况，screencap就不能显示了。

screenshot.update()是利用OpenGL来重新render，看下这部分：
status_t ScreenshotClient::update() {
    sp<ISurfaceComposer> s(ComposerService::getComposerService());
    if (s == NULL) return NO_INIT;
mHeap = 0;
/*s是指SurfacFlinger*/
    return s->captureScreen(0, &mHeap,
            &mWidth, &mHeight, &mFormat, 0, 0,
            0, -1UL);
}
status_t SurfaceFlinger::captureScreen(DisplayID dpy,
        sp<IMemoryHeap>* heap,
        uint32_t* width, uint32_t* height, PixelFormat* format,
        uint32_t sw, uint32_t sh,
        uint32_t minLayerZ, uint32_t maxLayerZ)
{


    // only one display supported for now
    if (CC_UNLIKELY(uint32_t(dpy) >= DISPLAY_COUNT))
        return BAD_VALUE;


    if (!GLExtensions::getInstance().haveFramebufferObject())
        return INVALID_OPERATION;

    class MessageCaptureScreen : public MessageBase {
        SurfaceFlinger* flinger;
        DisplayID dpy;
        sp<IMemoryHeap>* heap;
        uint32_t* w;
        uint32_t* h;
        PixelFormat* f;
        uint32_t sw;
        uint32_t sh;
        uint32_t minLayerZ;
        uint32_t maxLayerZ;
        status_t result;
    public:
        MessageCaptureScreen(SurfaceFlinger* flinger, DisplayID dpy,
                sp<IMemoryHeap>* heap, uint32_t* w, uint32_t* h, PixelFormat* f,
                uint32_t sw, uint32_t sh,
                uint32_t minLayerZ, uint32_t maxLayerZ)
            : flinger(flinger), dpy(dpy),
              heap(heap), w(w), h(h), f(f), sw(sw), sh(sh),
              minLayerZ(minLayerZ), maxLayerZ(maxLayerZ),
              result(PERMISSION_DENIED)
        {
        }
        status_t getResult() const {
            return result;
        }
        virtual bool handler() {
            Mutex::Autolock _l(flinger->mStateLock);

            // if we have secure windows, never allow the screen capture
            if (flinger->mSecureFrameBuffer)
                return true;

            result = flinger->captureScreenImplLocked(dpy,
                    heap, w, h, f, sw, sh, minLayerZ, maxLayerZ);

            return true;
        }
    };

    sp<MessageBase> msg = new MessageCaptureScreen(this,
            dpy, heap, width, height, format, sw, sh, minLayerZ, maxLayerZ);
	/*会调用自己的handle()函数*/
    status_t res = postMessageSync(msg);
    if (res == NO_ERROR) {
        res = static_cast<MessageCaptureScreen*>( msg.get() )->getResult();
    }
    return res;
}
status_t SurfaceFlinger::captureScreenImplLocked(DisplayID dpy,
        sp<IMemoryHeap>* heap,
        uint32_t* w, uint32_t* h, PixelFormat* f,
        uint32_t sw, uint32_t sh,
        uint32_t minLayerZ, uint32_t maxLayerZ)
{
    ATRACE_CALL();

    status_t result = PERMISSION_DENIED;

    // only one display supported for now
    if (CC_UNLIKELY(uint32_t(dpy) >= DISPLAY_COUNT))
        return BAD_VALUE;

	
    if (!GLExtensions::getInstance().haveFramebufferObject())
        return INVALID_OPERATION;

    // get screen geometry
    const DisplayHardware& hw(graphicPlane(dpy).displayHardware());
    const uint32_t hw_w = hw.getWidth();
    const uint32_t hw_h = hw.getHeight();

	/*ap申请的宽高是否合法*/
    if ((sw > hw_w) || (sh > hw_h))
        return BAD_VALUE;

    sw = (!sw) ? hw_w : sw;
    sh = (!sh) ? hw_h : sh;
    const size_t size = sw * sh * 4;

    //ALOGD("screenshot: sw=%d, sh=%d, minZ=%d, maxZ=%d",
    //        sw, sh, minLayerZ, maxLayerZ);

    // make sure to clear all GL error flags
    while ( glGetError() != GL_NO_ERROR ) ;

    // create a FBO
GLuint name, tname;
/*创建Renderbuffer对象*/
glGenRenderbuffersOES(1, &tname);
/*将Renderbuffer绑定到opengl库中*/
glBindRenderbufferOES(GL_RENDERBUFFER_OES, tname);
/*Renderbuffer本身不含有内存空间，需要分配*/
    glRenderbufferStorageOES(GL_RENDERBUFFER_OES, GL_RGBA8_OES, sw, sh);

	/*创建非屏幕显示的framebuffer 对象*/
glGenFramebuffersOES(1, &name);
/* 将Framebuffer绑定到Opengl库中*/
glBindFramebufferOES(GL_FRAMEBUFFER_OES, name);
/*将Renderbuffer链接到Framebuffer中*/
    glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES,
            GL_COLOR_ATTACHMENT0_OES, GL_RENDERBUFFER_OES, tname);

/*在上面的操作之后，对应的操作都是重定向到framebuffer对象中，而不是可见屏幕。*/

    GLenum status = glCheckFramebufferStatusOES(GL_FRAMEBUFFER_OES);

    if (status == GL_FRAMEBUFFER_COMPLETE_OES) {

        // invert everything, b/c glReadPixel() below will invert the FB
        glViewport(0, 0, sw, sh);
        glMatrixMode(GL_PROJECTION);
        glPushMatrix();
        glLoadIdentity();
        glOrthof(0, hw_w, hw_h, 0, 0, 1);
        glMatrixMode(GL_MODELVIEW);

        // redraw the screen entirely...
        glClearColor(0,0,0,1);
        glClear(GL_COLOR_BUFFER_BIT);

        const LayerVector& layers(mDrawingState.layersSortedByZ);
        const size_t count = layers.size();
        for (size_t i=0 ; i<count ; ++i) {
            const sp<LayerBase>& layer(layers[i]);
            const uint32_t flags = layer->drawingState().flags;
            if (!(flags & ISurfaceComposer::eLayerHidden)) {
                const uint32_t z = layer->drawingState().z;
                if (z >= minLayerZ && z <= maxLayerZ) {
                    layer->drawForSreenShot();
                }
            }
        }

        // check for errors and return screen capture
        if (glGetError() != GL_NO_ERROR) {
            // error while rendering
            result = INVALID_OPERATION;
        } else {
            // allocate shared memory large enough to hold the
            // screen capture
            sp<MemoryHeapBase> base(
                    new MemoryHeapBase(size, 0, "screen-capture") );
            void* const ptr = base->getBase();
            if (ptr) {
                // capture the screen with glReadPixels()
                ScopedTrace _t(ATRACE_TAG, "glReadPixels");
                glReadPixels(0, 0, sw, sh, GL_RGBA, GL_UNSIGNED_BYTE, ptr);
                if (glGetError() == GL_NO_ERROR) {
                    *heap = base;
                    *w = sw;
                    *h = sh;
                    *f = PIXEL_FORMAT_RGBA_8888;
                    result = NO_ERROR;
                }
            } else {
                result = NO_MEMORY;
            }
        }
        glViewport(0, 0, hw_w, hw_h);
        glMatrixMode(GL_PROJECTION);
        glPopMatrix();
        glMatrixMode(GL_MODELVIEW);
    } else {
        result = BAD_VALUE;
    }

    // release FBO resources
    glBindFramebufferOES(GL_FRAMEBUFFER_OES, 0);
    glDeleteRenderbuffersOES(1, &tname);
    glDeleteFramebuffersOES(1, &name);

    hw.compositionComplete();

    // ALOGD("screenshot: result = %s", result<0 ? strerror(result) : "OK");

    return result;
}

其中的layer->drawForSreenShot();会调用layerbase.cpp中的函数，然后相应地调用各种type的layer的ondraw函数，

一般情况下都是调用layer.cpp中的ondraw函数，最终调用drawWithOpenGL来render。

所以如果发现画面180°旋转的问题， 我们就可以在drawWithOpenGL这个函数里直接对mVertices做手脚了！

对于Framebuffer object,可参考如下文章,，解释的很好：

http://www.imobilebbs.com/wordpress/archives/3051

20130208