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Android Camera数据流分析全程记录（overlay方式二）

分类： Android平台

2014-03-20 17:17:24

原文地址： Android Camera数据流分析全程记录（overlay方式二） 作者：xinyuwuxian

 Android Camera数据流分析全程记录（overlay方式）

这篇文章接着上一篇文章继续：http://blog.chinaunix.net/uid-26765074-id-3568436.html
上一篇文章overlay这个过程已经走了一遍，但是根本是这个流程还没有走完，由上一篇文章知道，最后调用了postFrame方法，postFrame这个方法都实现了什么样的功能呢？？？他是怎样是的从driver获得的数据最终显示成图像的呢？？
这个问题我一直在寻求答案，不过很悲催啊？？这个postFrame方法我始终没有理解清楚，这里有多少说多少自己的看法，希望有大神能指点指点
这里就从postFrame入手了：
  1. status_t ANativeWindowDisplayAdapter::PostFrame(ANativeWindowDisplayAdapter::DisplayFrame &dispFrame)
  2. {
  3.     status_t ret = NO_ERROR;
  4.     uint32_t actualFramesWithDisplay = 0;
  5.     android_native_buffer_t *buffer = NULL;
  6.     GraphicBufferMapper &mapper = GraphicBufferMapper::get();
  7.     int i;

  9.     ///@todo Do cropping based on the stabilized frame coordinates
  10.     ///@todo Insert logic to drop frames here based on refresh rate of
  11.     ///display or rendering rate whichever is lower
  12.     ///Queue the buffer to overlay

  14.     if ( NULL == mANativeWindow ) {
  15.         return NO_INIT;
  16.     }

  18.     if (!mBuffers || !dispFrame.mBuffer) {
  19.         CAMHAL_LOGEA("NULL sent to PostFrame");
  20.         return BAD_VALUE;
  21.     }

  23.     for ( i = 0; i < mBufferCount; i++ )
  24.         {
  25.         if ( dispFrame.mBuffer == &mBuffers[i] )
  26.             {
  27.             break;
  28.         }
  29.     }


  32.     mFramesType.add( (int)mBuffers[i].opaque ,dispFrame.mType );

  34.     if ( mDisplayState == ANativeWindowDisplayAdapter::DISPLAY_STARTED &&
  35.                 (!mPaused || CameraFrame::CameraFrame::SNAPSHOT_FRAME == dispFrame.mType) &&
  36.                 !mSuspend)
  37.     {
  38.         Mutex::Autolock lock(mLock);
  39.         uint32_t xOff = (dispFrame.mOffset% PAGE_SIZE);
  40.         uint32_t yOff = (dispFrame.mOffset / PAGE_SIZE);

  42.         // Set crop only if current x and y offsets do not match with frame offsets
  43.         if((mXOff!=xOff) || (mYOff!=yOff))
  44.         {
  45.             CAMHAL_LOGDB("Offset %d xOff = %d, yOff = %d", dispFrame.mOffset, xOff, yOff);
  46.             uint8_t bytesPerPixel;
  47.             ///Calculate bytes per pixel based on the pixel format
  48.             if(strcmp(mPixelFormat, (const char *) CameraParameters::PIXEL_FORMAT_YUV422I) == 0)
  49.                 {
  50.                 bytesPerPixel = 2;
  51.                 }
  52.             else if(strcmp(mPixelFormat, (const char *) CameraParameters::PIXEL_FORMAT_RGB565) == 0)
  53.                 {
  54.                 bytesPerPixel = 2;
  55.                 }
  56.             else if(strcmp(mPixelFormat, (const char *) CameraParameters::PIXEL_FORMAT_YUV420SP) == 0)
  57.                 {
  58.                 bytesPerPixel = 1;
  59.                 }
  60.             else
  61.                 {
  62.                 bytesPerPixel = 1;
  63.             }

  65.             CAMHAL_LOGVB(" crop.left = %d crop.top = %d crop.right = %d crop.bottom = %d",
  66.                           xOff/bytesPerPixel, yOff , (xOff/bytesPerPixel)+mPreviewWidth, yOff+mPreviewHeight);
  67.             // We'll ignore any errors here, if the surface is
  68.             // already invalid, we'll know soon enough.
  69.             mANativeWindow->set_crop(mANativeWindow, xOff/bytesPerPixel, yOff,
  70.                                      (xOff/bytesPerPixel)+mPreviewWidth, yOff+mPreviewHeight);

  72.             ///Update the current x and y offsets
  73.             mXOff = xOff;
  74.             mYOff = yOff;
  75.         }
  76.         //这里说说自己对以上代码的理解，上面通过传入的displayFrame类型变量check，传入的配置是否与系统此时实际显示属性一致，不一致，则从新进行裁剪，配置显示大小，位置等
  77.         {
  78.             buffer_handle_t *handle = (buffer_handle_t *) mBuffers[i].opaque;
  79.             // unlock buffer before sending to display
  80.             mapper.unlock(*handle);
  81.             ret = mANativeWindow->enqueue_buffer(mANativeWindow, handle);//这里将buffer入栈，下面会分析道这个函数的由来
  82.         }
  83.         if ( NO_ERROR != ret ) {
  84.             CAMHAL_LOGE("Surface::queueBuffer returned error %d", ret);
  85.         }

  87.         mFramesWithCameraAdapterMap.removeItem((buffer_handle_t *) dispFrame.mBuffer->opaque);


  90.         // HWComposer has not minimum buffer requirement. We should be able to dequeue
  91.         // the buffer immediately
  92.         TIUTILS::Message msg;
  93.         mDisplayQ.put(&msg);


  96. #if PPM_INSTRUMENTATION || PPM_INSTRUMENTATION_ABS

  98.         if ( mMeasureStandby )
  99.             {
  100.             CameraHal::PPM("Standby to first shot: Sensor Change completed - ", &mStandbyToShot);
  101.             mMeasureStandby = false;
  102.             }
  103.         else if (CameraFrame::CameraFrame::SNAPSHOT_FRAME == dispFrame.mType)
  104.             {
  105.             CameraHal::PPM("Shot to snapshot: ", &mStartCapture);
  106.             mShotToShot = true;
  107.             }
  108.         else if ( mShotToShot )
  109.             {
  110.             CameraHal::PPM("Shot to shot: ", &mStartCapture);
  111.             mShotToShot = false;
  112.         }
  113. #endif

  115.     }
  116.     else
  117.     {
  118.         Mutex::Autolock lock(mLock);
  119.         buffer_handle_t *handle = (buffer_handle_t *) mBuffers[i].opaque;

  121.         // unlock buffer before giving it up
  122.         mapper.unlock(*handle);

  124.         // cancel buffer and dequeue another one
  125.         ret = mANativeWindow->cancel_buffer(mANativeWindow, handle);
  126.         if ( NO_ERROR != ret ) {
  127.             CAMHAL_LOGE("Surface::cancelBuffer returned error %d", ret);
  128.         }

  130.         mFramesWithCameraAdapterMap.removeItem((buffer_handle_t *) dispFrame.mBuffer->opaque);

  132.         TIUTILS::Message msg;
  133.         mDisplayQ.put(&msg);
  134.         ret = NO_ERROR;
  135.     }

  137.     return ret;
  138. }
我们还是着重分析一下这个方法吧：mANativeWindow->enqueue_buffer(mANativeWindow, handle)
首先要找的mANativewindow这个变量类型的定义，找了好久才找到的，悲催：system\core\include\system\Window.h
  1. struct ANativeWindow
  2. {
  3. #ifdef __cplusplus
  4.     ANativeWindow()
  5.         : flags(0), minSwapInterval(0), maxSwapInterval(0), xdpi(0), ydpi(0)
  6.     {
  7.         common.magic = ANDROID_NATIVE_WINDOW_MAGIC;
  8.         common.version = sizeof(ANativeWindow);
  9.         memset(common.reserved, 0, sizeof(common.reserved));
  10.     }

  12.     /* Implement the methods that sp<ANativeWindow> expects so that it
  13.        can be used to automatically refcount ANativeWindow's. */
  14.     void incStrong(const void* id) const {
  15.         common.incRef(const_cast<android_native_base_t*>(&common));
  16.     }
  17.     void decStrong(const void* id) const {
  18.         common.decRef(const_cast<android_native_base_t*>(&common));
  19.     }
  20. #endif

  22.     struct android_native_base_t common;

  24.     /* flags describing some attributes of this surface or its updater */
  25.     const uint32_t flags;

  27.     /* min swap interval supported by this updated */
  28.     const int minSwapInterval;

  30.     /* max swap interval supported by this updated */
  31.     const int maxSwapInterval;

  33.     /* horizontal and vertical resolution in DPI */
  34.     const float xdpi;
  35.     const float ydpi;

  37.     /* Some storage reserved for the OEM's driver. */
  38.     intptr_t oem[4];

  40.     /*
  41.      * Set the swap interval for this surface.
  42.      *
  43.      * Returns 0 on success or -errno on error.
  44.      */
  45.     int (*setSwapInterval)(struct ANativeWindow* window, int interval);

  47.     /*
  48.      * hook called by EGL to acquire a buffer. After this call, the buffer
  49.      * is not locked, so its content cannot be modified.
  50.      * this call may block if no buffers are available.
  51.      *
  52.      * Returns 0 on success or -errno on error.
  53.      */
  54.     int (*dequeueBuffer)(struct ANativeWindow* window, struct ANativeWindowBuffer** buffer);

  56.     /*
  57.      * hook called by EGL to lock a buffer. This MUST be called before modifying
  58.      * the content of a buffer. The buffer must have been acquired with
  59.      * dequeueBuffer first.
  60.      *
  61.      * Returns 0 on success or -errno on error.
  62.      */
  63.     int (*lockBuffer)(struct ANativeWindow* window, struct ANativeWindowBuffer* buffer);
  64.    /*
  65.     * hook called by EGL when modifications to the render buffer are done.
  66.     * This unlocks and post the buffer.
  67.     *
  68.     * Buffers MUST be queued in the same order than they were dequeued.
  69.     *
  70.     * Returns 0 on success or -errno on error.
  71.     */
  72.     int (*queueBuffer)(struct ANativeWindow* window, struct ANativeWindowBuffer* buffer);

  74.     /*
  75.      * hook used to retrieve information about the native window.
  76.      *
  77.      * Returns 0 on success or -errno on error.
  78.      */
  79.     int (*query)(const struct ANativeWindow* window, int what, int* value);

  81.     /*
  82.      * hook used to perform various operations on the surface.
  83.      * (*perform)() is a generic mechanism to add functionality to
  84.      * ANativeWindow while keeping backward binary compatibility.
  85.      *
  86.      * DO NOT CALL THIS HOOK DIRECTLY. Instead, use the helper functions
  87.      * defined below.
  88.      *
  89.      * (*perform)() returns -ENOENT if the 'what' parameter is not supported
  90.      * by the surface's implementation.
  91.      *
  92.      * The valid operations are:
  93.      * NATIVE_WINDOW_SET_USAGE
  94.      * NATIVE_WINDOW_CONNECT (deprecated)
  95.      * NATIVE_WINDOW_DISCONNECT (deprecated)
  96.      * NATIVE_WINDOW_SET_CROP
  97.      * NATIVE_WINDOW_SET_BUFFER_COUNT
  98.      * NATIVE_WINDOW_SET_BUFFERS_GEOMETRY (deprecated)
  99.      * NATIVE_WINDOW_SET_BUFFERS_TRANSFORM
  100.      * NATIVE_WINDOW_SET_BUFFERS_TIMESTAMP
  101.      * NATIVE_WINDOW_SET_BUFFERS_DIMENSIONS
  102.      * NATIVE_WINDOW_SET_BUFFERS_FORMAT
  103.      * NATIVE_WINDOW_SET_SCALING_MODE
  104.      * NATIVE_WINDOW_LOCK (private)
  105.      * NATIVE_WINDOW_UNLOCK_AND_POST (private)
  106.      * NATIVE_WINDOW_API_CONNECT (private)
  107.      * NATIVE_WINDOW_API_DISCONNECT (private)
  108.      *
  109.      */

  111.     int (*perform)(struct ANativeWindow* window, int operation, ... );

  113.     /*
  114.      * hook used to cancel a buffer that has been dequeued.
  115.      * No synchronization is performed between dequeue() and cancel(), so
  116.      * either external synchronization is needed, or these functions must be
  117.      * called from the same thread.
  118.      */
  119.     int (*cancelBuffer)(struct ANativeWindow* window, struct ANativeWindowBuffer* buffer);


  122.     void* reserved_proc[2];
  123. };
既然上面调用了这个对象的方法，那么必然你要找到他的方法是在什么地方实现的，怎么实现的
我们首先看看mANativewindow到底前身是什么，我们调用的这个方法到底是在哪里实现的，首先我们看一下他是从哪里引入进来的？？
  1. int ANativeWindowDisplayAdapter::setPreviewWindow(preview_stream_ops_t* window)
  2. {
  3.     LOG_FUNCTION_NAME;
  4.     ///Note that Display Adapter cannot work without a valid window object
  5.     if ( !window)
  6.         {
  7.         CAMHAL_LOGEA("NULL window object passed to DisplayAdapter");
  8.         LOG_FUNCTION_NAME_EXIT;
  9.         return BAD_VALUE;
  10.     }

  12.     if ( window == mANativeWindow ) {
  13.         return ALREADY_EXISTS;
  14.     }

  16.     ///Destroy the existing window object, if it exists
  17.     destroy();

  19.     ///Move to new window obj
  20.     mANativeWindow = window;

  22.     LOG_FUNCTION_NAME_EXIT;

  24.     return NO_ERROR;
  25. }
这个window参数最终要往上层追溯，我们这里直接说了，其实window的初始化定义在hardware interface那里，和camera service在一个目录下
  1. /** Set the ANativeWindow to which preview frames are sent */
  2.     status_t setPreviewWindow(const sp<ANativeWindow>& buf)
  3.     {
  4.         LOGV("%s(%s) buf %p", __FUNCTION__, mName.string(), buf.get());

  6.         if (mDevice->ops->set_preview_window) {
  7.             mPreviewWindow = buf;
  8. #ifdef OMAP_ENHANCEMENT_CPCAM
  9.             mHalPreviewWindow.user = mPreviewWindow.get();
  10. #else
  11.             mHalPreviewWindow.user = this;
  12. #endif
  13.             LOGV("%s &mHalPreviewWindow %p mHalPreviewWindow.user %p", __FUNCTION__,
  14.                     &mHalPreviewWindow, mHalPreviewWindow.user);
  15.             return mDevice->ops->set_preview_window(mDevice, buf.get() ? &mHalPreviewWindow.nw : 0);
  16.         }
  17.         return INVALID_OPERATION;
  18.     }
上面我们看到，window通过mHalPreviewWindow传入到底层，我们还是要看看mHalPreviewWindow这个变量的初始化和实现在哪里？？
  1. status_t initialize(hw_module_t *module)
  2.     {
  3.         LOGI("Opening camera %s", mName.string());
  4.         int rc = module->methods->open(module, mName.string(),
  5.                                        (hw_device_t **)&mDevice);
  6.         if (rc != OK) {
  7.             LOGE("Could not open camera %s: %d", mName.string(), rc);
  8.             return rc;
  9.         }
  10. #ifdef OMAP_ENHANCEMENT_CPCAM
  11.         initHalPreviewWindow(&mHalPreviewWindow);
  12.         initHalPreviewWindow(&mHalTapin);
  13.         initHalPreviewWindow(&mHalTapout);
  14. #else
  15.         initHalPreviewWindow();
  16. #endif
  17.         return rc;
  18.     }
在最初打开camera的时候会调用上面initialize方法，通过initHalPreviewWindow这个方法实现mHalPrevieWindow的初始化以及hal层需要方法是实现
  1.     void initHalPreviewWindow(struct camera_preview_window *window)
  2.     {

  4.         window->nw.cancel_buffer = __cancel_buffer;
  5.         window->nw.lock_buffer = __lock_buffer;
  6.         window->nw.dequeue_buffer = __dequeue_buffer;
  7.         window->nw.enqueue_buffer = __enqueue_buffer;
  8.         window->nw.set_buffer_count = __set_buffer_count;
  9.         window->nw.set_buffers_geometry = __set_buffers_geometry;
  10.         window->nw.set_crop = __set_crop;
  11.         window->nw.set_metadata = __set_metadata;
  12.         window->nw.set_usage = __set_usage;
  13.         window->nw.set_swap_interval = __set_swap_interval;
  14.         window->nw.update_and_get_buffer = __update_and_get_buffer;
  15.         window->nw.get_metadata = __get_metadata;
  16.         window->nw.get_buffer_dimension = __get_buffer_dimension;
  17.         window->nw.get_buffer_format = __get_buffer_format;

  19.         window->nw.get_min_undequeued_buffer_count =
  20.                 __get_min_undequeued_buffer_count;
  21.     }
这里进行了填充，我们就看看cancel_buffer方法的实现吧

  1.     static int __cancel_buffer(struct preview_stream_ops* w,
  2.                       buffer_handle_t* buffer)
  3.     {
  4.         ANativeWindow *a = anw(w);
  5.         return a->cancelBuffer(a,container_of(buffer, ANativeWindowBuffer, handle));
  6.     }
这里只是作为一个转接点，没有做任何事情，而是直接去调用了其他实现了的方法实现操作
这里通过anm这个方法转换而来的ANativeWindow类型的变量a其实就是我们在上面initialize方式中初始化的mPreviewWindow 
而这个mPreviewWindow 就是上层传下来的的surface

这里是camera service层，个人认为是在这里对window这个参数进行了配置，连接api...还有其他的操作
  1. status_t CameraService::Client::setPreviewWindow(const sp<IBinder>& binder,
  2.         const sp<ANativeWindow>& window) {
  3.     Mutex::Autolock lock(mLock);
  4.     status_t result = checkPidAndHardware();
  5.     if (result != NO_ERROR) return result;

  7.     // return if no change in surface.
  8.     if (binder == mSurface) {
  9.         return NO_ERROR;
  10.     }

  12.     if (window != 0) {
  13.         result = native_window_api_connect(window.get(), NATIVE_WINDOW_API_CAMERA);
  14.         if (result != NO_ERROR) {
  15.             LOGE("native_window_api_connect failed: %s (%d)", strerror(-result),
  16.                     result);
  17.             return result;
  18.         }
  19.     }

  21.     // If preview has been already started, register preview buffers now.
  22.     if (mHardware->previewEnabled()) {
  23.         if (window != 0) {
  24.             native_window_set_scaling_mode(window.get(), NATIVE_WINDOW_SCALING_MODE_SCALE_TO_WINDOW);
  25.             native_window_set_buffers_transform(window.get(), mOrientation);
  26.             result = mHardware->setPreviewWindow(window);
  27.         }
  28.     }

  30.     if (result == NO_ERROR) {
  31.         // Everything has succeeded. Disconnect the old window and remember the
  32.         // new window.
  33.         disconnectWindow(mPreviewWindow);
  34.         mSurface = binder;
  35.         mPreviewWindow = window;
  36.     } else {
  37.         // Something went wrong after we connected to the new window, so
  38.         // disconnect here.
  39.         disconnectWindow(window);
  40.     }

  42.     return result;
  43. }
这里我还是暂时不做说明吧，始终不是很理解这里为什么要这样做，一直以来上面调用的cancelBuffer方法到底是在哪里实现的，这个问题纠结了我很久
这里先说说现在的想法，自己的理解，maybe wrong
这里跳度很大，看看下面的方法，来源:frameworks\base\libs\gui\SurfaceTextureClient.cpp
说的是SurfaceTextureClient类的构造方法
  1. SurfaceTextureClient::SurfaceTextureClient(
  2.         const sp<ISurfaceTexture>& surfaceTexture)
  3. {
  4.     SurfaceTextureClient::init();
  5.     SurfaceTextureClient::setISurfaceTexture(surfaceTexture);
  6. }
先看看init方法:

  1. void SurfaceTextureClient::init() {
  2.     // Initialize the ANativeWindow function pointers.
  3.     ANativeWindow::setSwapInterval = hook_setSwapInterval;
  4.     ANativeWindow::dequeueBuffer = hook_dequeueBuffer;
  5.     ANativeWindow::cancelBuffer = hook_cancelBuffer;
  6.     ANativeWindow::lockBuffer = hook_lockBuffer;
  7.     ANativeWindow::queueBuffer = hook_queueBuffer;
  8.     ANativeWindow::query = hook_query;
  9.     ANativeWindow::perform = hook_perform;

  11.     const_cast<int&>(ANativeWindow::minSwapInterval) = 0;
  12.     const_cast<int&>(ANativeWindow::maxSwapInterval) = 1;

  14.     mReqWidth = 0;
  15.     mReqHeight = 0;
  16.     mReqFormat = 0;
  17.     mReqUsage = 0;
  18.     mTimestamp = NATIVE_WINDOW_TIMESTAMP_AUTO;
  19.     mDefaultWidth = 0;
  20.     mDefaultHeight = 0;
  21.     mTransformHint = 0;
  22.     mConnectedToCpu = false;
  23. }
重点是上面我标注出来的部分，就现在的理解，这里就是上面说的cancelBuffer方法的归宿了，另外包括其他的所有方法，方法基本相同，这里为方便分析理解
我们以dequeueBuffer为例进行讲解，那就先看看hook_dequeueBuffer的实现
  1. int SurfaceTextureClient::hook_dequeueBuffer(ANativeWindow* window,
  2.         ANativeWindowBuffer** buffer) {
  3.     SurfaceTextureClient* c = getSelf(window);
  4.     return c->dequeueBuffer(buffer);
  5. }
接着调用SurfaceTextureClient类的dequeueBuffer方法

  1. int SurfaceTextureClient::dequeueBuffer(android_native_buffer_t** buffer) {
  2.     LOGV("SurfaceTextureClient::dequeueBuffer");
  3.     Mutex::Autolock lock(mMutex);
  4.     int buf = -1;
  5.     status_t result = mSurfaceTexture->dequeueBuffer(&buf, mReqWidth, mReqHeight,mReqFormat, mReqUsage);
  6.     if (result < 0) {
  7.         LOGV("dequeueBuffer: ISurfaceTexture::dequeueBuffer(%d, %d, %d, %d)"
  8.              "failed: %d", mReqWidth, mReqHeight, mReqFormat, mReqUsage,
  9.              result);
  10.         return result;
  11.     }
  12.     sp<GraphicBuffer>& gbuf(mSlots[buf]);
  13.     if (result & ISurfaceTexture::RELEASE_ALL_BUFFERS) {
  14.         freeAllBuffers();
  15.     }

  17.     if ((result & ISurfaceTexture::BUFFER_NEEDS_REALLOCATION) || gbuf == 0) {
  18.         result = mSurfaceTexture->requestBuffer(buf, &gbuf);
  19.         if (result != NO_ERROR) {
  20.             LOGE("dequeueBuffer: ISurfaceTexture::requestBuffer failed: %d",
  21.                     result);
  22.             return result;
  23.         }
  24.     }
  25.     *buffer = gbuf.get();
  26.     return OK;
  27. }
我们需要先找到mSurfaceTexture是在哪里定义的：system\media\mca\filterpacks\videosrc\java\CameraSource.java
private SurfaceTexture mSurfaceTexture;
接下来看看他是在哪里实例化的
  1. @Override
  2.     public void open(FilterContext context) {
  3.         if (mLogVerbose) Log.v(TAG, "Opening");
  4.         // Open camera
  5.         mCamera = Camera.open(mCameraId);

  7.         // Set parameters
  8.         getCameraParameters();
  9.         mCamera.setParameters(mCameraParameters);

  11.         // Create frame formats
  12.         createFormats();

  14.         // Bind it to our camera frame
  15.         mCameraFrame = (GLFrame)context.getFrameManager().newBoundFrame(mOutputFormat,
  16.                                                                         GLFrame.EXTERNAL_TEXTURE,
  17.                                                                         0);
  18.         mSurfaceTexture = new SurfaceTexture(mCameraFrame.getTextureId());
  19.         try {
  20.             mCamera.setPreviewTexture(mSurfaceTexture);
  21.         } catch (IOException e) {
  22.             throw new RuntimeException("Could not bind camera surface texture: " +
  23.                                        e.getMessage() + "!");
  24.         }

  26.         // Connect SurfaceTexture to callback
  27.         mSurfaceTexture.setOnFrameAvailableListener(onCameraFrameAvailableListener);
  28.         // Start the preview
  29.         mNewFrameAvailable = false;
  30.         mCamera.startPreview();
  31.     }
其他方法先不做过多分析，这里实例化了SurfaceTexture的对象，看看他的构造函数：frameworks\base\libs\gui\SurfaceTexture.cpp

  1. SurfaceTexture::SurfaceTexture(GLuint tex, bool allowSynchronousMode,
  2.         GLenum texTarget) :
  3.     mDefaultWidth(1),
  4.     mDefaultHeight(1),
  5.     mPixelFormat(PIXEL_FORMAT_RGBA_8888),
  6.     mBufferCount(MIN_ASYNC_BUFFER_SLOTS),
  7.     mClientBufferCount(0),
  8.     mServerBufferCount(MIN_ASYNC_BUFFER_SLOTS),
  9.     mCurrentTexture(INVALID_BUFFER_SLOT),
  10.     mCurrentTransform(0),
  11.     mCurrentTimestamp(0),
  12.     mNextTransform(0),
  13.     mNextScalingMode(NATIVE_WINDOW_SCALING_MODE_FREEZE),
  14.     mTexName(tex),
  15.     mSynchronousMode(false),
  16.     mAllowSynchronousMode(allowSynchronousMode),
  17.     mConnectedApi(NO_CONNECTED_API),
  18.     mAbandoned(false),
  19.     mTexTarget(texTarget) {
  20.     // Choose a name using the PID and a process-unique ID.
  21.     mName = String8::format("unnamed-%d-%d", getpid(), createProcessUniqueId());

  23.     ST_LOGV("SurfaceTexture::SurfaceTexture");
  24.     sp<ISurfaceComposer> composer(ComposerService::getComposerService());
  25.     mGraphicBufferAlloc = composer->createGraphicBufferAlloc();
  26.     mNextCrop.makeInvalid();
  27.     memcpy(mCurrentTransformMatrix, mtxIdentity,
  28.             sizeof(mCurrentTransformMatrix));
  29. }
我们接着往下看，mSurfaceTexture->dequeueBuffer(&buf, mReqWidth, mReqHeight,mReqFormat, mReqUsage);
这里调用了类SurfaceTexture的方法dequeueBuffer

  1. status_t SurfaceTexture::dequeueBuffer(int *outBuf, uint32_t w, uint32_t h,
  2.         uint32_t format, uint32_t usage) {
  3.     ST_LOGV("SurfaceTexture::dequeueBuffer");

  5.     if ((w && !h) || (!w && h)) {
  6.         ST_LOGE("dequeueBuffer: invalid size: w=%u, h=%u", w, h);
  7.         return BAD_VALUE;
  8.     }

  10.     Mutex::Autolock lock(mMutex);

  12.     status_t returnFlags(OK);

  14.     int found, foundSync;
  15.     int dequeuedCount = 0;
  16.     bool tryAgain = true;
  17.     while (tryAgain) {
  18.         if (mAbandoned) {
  19.             ST_LOGE("dequeueBuffer: SurfaceTexture has been abandoned!");
  20.             return NO_INIT;
  21.         }

  23.         // We need to wait for the FIFO to drain if the number of buffer
  24.         // needs to change.
  25.         //
  26.         // The condition "number of buffers needs to change" is true if
  27.         // - the client doesn't care about how many buffers there are
  28.         // - AND the actual number of buffer is different from what was
  29.         // set in the last setBufferCountServer()
  30.         // - OR -
  31.         // setBufferCountServer() was set to a value incompatible with
  32.         // the synchronization mode (for instance because the sync mode
  33.         // changed since)
  34.         //
  35.         // As long as this condition is true AND the FIFO is not empty, we
  36.         // wait on mDequeueCondition.

  38.         const int minBufferCountNeeded = mSynchronousMode ?
  39.                 MIN_SYNC_BUFFER_SLOTS : MIN_ASYNC_BUFFER_SLOTS;

  41.         const bool numberOfBuffersNeedsToChange = !mClientBufferCount &&
  42.                 ((mServerBufferCount != mBufferCount) ||
  43.                         (mServerBufferCount < minBufferCountNeeded));

  45.         if (!mQueue.isEmpty() && numberOfBuffersNeedsToChange) {
  46.             // wait for the FIFO to drain
  47.             mDequeueCondition.wait(mMutex);
  48.             // NOTE: we continue here because we need to reevaluate our
  49.             // whole state (eg: we could be abandoned or disconnected)
  50.             continue;
  51.         }

  53.         if (numberOfBuffersNeedsToChange) {
  54.             // here we're guaranteed that mQueue is empty
  55.             freeAllBuffersLocked();
  56.             mBufferCount = mServerBufferCount;
  57.             if (mBufferCount < minBufferCountNeeded)
  58.                 mBufferCount = minBufferCountNeeded;
  59.             mCurrentTexture = INVALID_BUFFER_SLOT;
  60.             returnFlags |= ISurfaceTexture::RELEASE_ALL_BUFFERS;
  61.         }

  63.         // look for a free buffer to give to the client
  64.         found = INVALID_BUFFER_SLOT;
  65.         foundSync = INVALID_BUFFER_SLOT;
  66.         dequeuedCount = 0;
  67.         for (int i = 0; i < mBufferCount; i++) {
  68.             const int state = mSlots[i].mBufferState;
  69.             if (state == BufferSlot::DEQUEUED) {
  70.                 dequeuedCount++;
  71.             }

  73.             // if buffer is FREE it CANNOT be current
  74.             LOGW_IF((state == BufferSlot::FREE) && (mCurrentTexture==i),
  75.                     "dequeueBuffer: buffer %d is both FREE and current!", i);

  77.             if (ALLOW_DEQUEUE_CURRENT_BUFFER) {
  78.                 if (state == BufferSlot::FREE || i == mCurrentTexture) {
  79.                     foundSync = i;
  80.                     if (i != mCurrentTexture) {
  81.                         found = i;
  82.                         break;
  83.                     }
  84.                 }
  85.             } else {
  86.                 if (state == BufferSlot::FREE) {
  87.                     foundSync = i;
  88.                     found = i;
  89.                     break;
  90.                 }
  91.             }
  92.         }

  94.         // clients are not allowed to dequeue more than one buffer
  95.         // if they didn't set a buffer count.
  96.         if (!mClientBufferCount && dequeuedCount) {
  97.             return -EINVAL;
  98.         }

  100.         // See whether a buffer has been queued since the last setBufferCount so
  101.         // we know whether to perform the MIN_UNDEQUEUED_BUFFERS check below.
  102.         bool bufferHasBeenQueued = mCurrentTexture != INVALID_BUFFER_SLOT;
  103.         if (bufferHasBeenQueued) {
  104.             // make sure the client is not trying to dequeue more buffers
  105.             // than allowed.
  106.             const int avail = mBufferCount - (dequeuedCount+1);
  107.             if (avail < (MIN_UNDEQUEUED_BUFFERS-int(mSynchronousMode))) {
  108.                 ST_LOGE("dequeueBuffer: MIN_UNDEQUEUED_BUFFERS=%d exceeded "
  109.                         "(dequeued=%d)",
  110.                         MIN_UNDEQUEUED_BUFFERS-int(mSynchronousMode),
  111.                         dequeuedCount);
  112.                 return -EBUSY;
  113.             }
  114.         }

  116.         // we're in synchronous mode and didn't find a buffer, we need to wait
  117.         // for some buffers to be consumed
  118.         tryAgain = mSynchronousMode && (foundSync == INVALID_BUFFER_SLOT);
  119.         if (tryAgain) {
  120.             mDequeueCondition.wait(mMutex);
  121.         }
  122.     }

  124.     if (mSynchronousMode && found == INVALID_BUFFER_SLOT) {
  125.         // foundSync guaranteed to be != INVALID_BUFFER_SLOT
  126.         found = foundSync;
  127.     }

  129.     if (found == INVALID_BUFFER_SLOT) {
  130.         return -EBUSY;
  131.     }

  133.     const int buf = found;
  134.     *outBuf = found;

  136.     const bool useDefaultSize = !w && !h;
  137.     if (useDefaultSize) {
  138.         // use the default size
  139.         w = mDefaultWidth;
  140.         h = mDefaultHeight;
  141.     }

  143.     const bool updateFormat = (format != 0);
  144.     if (!updateFormat) {
  145.         // keep the current (or default) format
  146.         format = mPixelFormat;
  147.     }

  149.     // buffer is now in DEQUEUED (but can also be current at the same time,
  150.     // if we're in synchronous mode)
  151.     mSlots[buf].mBufferState = BufferSlot::DEQUEUED;

  153.     const sp<GraphicBuffer>& buffer(mSlots[buf].mGraphicBuffer);
  154.     if ((buffer == NULL) ||
  155.         (uint32_t(buffer->width) != w) ||
  156.         (uint32_t(buffer->height) != h) ||
  157.         (uint32_t(buffer->format) != format) ||
  158.         ((uint32_t(buffer->usage) & usage) != usage))
  159.     {
  160.         usage |= GraphicBuffer::USAGE_HW_TEXTURE;
  161.         status_t error;
  162.         sp<GraphicBuffer> graphicBuffer(
  163.                 mGraphicBufferAlloc->createGraphicBuffer(
  164.                         w, h, format, usage, &error));
  165.         if (graphicBuffer == 0) {
  166.             ST_LOGE("dequeueBuffer: SurfaceComposer::createGraphicBuffer "
  167.                     "failed");
  168.             return error;
  169.         }
  170.         if (updateFormat) {
  171.             mPixelFormat = format;
  172.         }
  173.         mSlots[buf].mGraphicBuffer = graphicBuffer;
  174.         mSlots[buf].mRequestBufferCalled = false;
  175.         if (mSlots[buf].mEglImage != EGL_NO_IMAGE_KHR) {
  176.             eglDestroyImageKHR(mSlots[buf].mEglDisplay, mSlots[buf].mEglImage);
  177.             mSlots[buf].mEglImage = EGL_NO_IMAGE_KHR;
  178.             mSlots[buf].mEglDisplay = EGL_NO_DISPLAY;
  179.         }
  180.         returnFlags |= ISurfaceTexture::BUFFER_NEEDS_REALLOCATION;
  181.     }
  182.     return returnFlags;
  183. }
到这里为止，其实底层调用的那些方法最终在这里都有实现，应该也已经走到了系统的ui层，本想到此为止，我还是深入看看这个方法吧
很纠结啊，看的

当已存在申请的buffer，返回buffer序号
在初始化SurfaceTexture对象时，上面的构造函数中实例化mGraphicBufferAlloc = composer->createGraphicBufferAlloc();
createGraphicBufferAlloc的实现在以下路径：frameworks\base\libs\gui\ISurfaceComposer.cpp
  1. virtual sp<IGraphicBufferAlloc> createGraphicBufferAlloc()
  2.     {
  3.         uint32_t n;
  4.         Parcel data, reply;
  5.         data.writeInterfaceToken(ISurfaceComposer::getInterfaceDescriptor());
  6.         remote()->transact(BnSurfaceComposer::CREATE_GRAPHIC_BUFFER_ALLOC, data, &reply);
  7.         return interface_cast<IGraphicBufferAlloc>(reply.readStrongBinder());
  8.     }
由上面接着他会调用IGraphicBufferAlloc::createGraphicBuffer()，路径：frameworks\base\libs\gui\IGraphicBufferAlloc.cpp

  1. virtual sp<GraphicBuffer> createGraphicBuffer(uint32_t w, uint32_t h,
  2.             PixelFormat format, uint32_t usage, status_t* error) {
  3.         Parcel data, reply;
  4.         data.writeInterfaceToken(IGraphicBufferAlloc::getInterfaceDescriptor());
  5.         data.writeInt32(w);
  6.         data.writeInt32(h);
  7.         data.writeInt32(format);
  8.         data.writeInt32(usage);
  9.         remote()->transact(CREATE_GRAPHIC_BUFFER, data, &reply);
  10.         sp<GraphicBuffer> graphicBuffer;
  11.         status_t result = reply.readInt32();
  12.         if (result == NO_ERROR) {
  13.             graphicBuffer = new GraphicBuffer();
  14.             reply.read(*graphicBuffer);
  15.             // reply.readStrongBinder();
  16.             // here we don't even have to read the BufferReference from
  17.             // the parcel, it'll die with the parcel.
  18.         }
  19.         *error = result;
  20.         return graphicBuffer;
  21.     }
这里实例化GraphicBuffer类的对象，并且用返回的这个对象实例化graphicBuffer变量

这篇文章写得很吃力，不是理解的很透彻，其中可能很多思路根本就是错误的，待修正啊。。

待续。。。。
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