人类的悲欢并不相通---鲁迅

• Android Camera系列（一）：SurfaceView+Camera
• Android Camera系列（二）：TextureView+Camera
• Android Camera系列（三）：GLSurfaceView+Camera

本系列主要讲述Android开发中Camera的相关操作、预览方式、视频录制等。项目结构简单、代码耦合性低，旨在帮助大家能从中有所收获（方便copy :） ），对于个人来说也是一个总结的好机会

本章我们来讲解GLSurfaceView进行Camera预览，基于第一篇Android Camera系列（一）：SurfaceView+Camera的成果，我们已经对Camera进行了封装，CameraManager拿来直接使用就好

一.GLSurfaceView使用

GLSurfaceView实际上就是继承了SurfaceView，并在其内部封装了EGL环境管理和渲染线程，不了解EGL的请移步至Android OpenGLES开发：EGL环境搭建，使得我们可以直接使用OpenGL ES的API对图像进行变换等操作，如：黑白滤镜、美颜等各种复杂的滤镜效果

1. 自定义CameraGLSurfaceView继承GLSurfaceView
2. 实现SurfaceTexture.OnFrameAvailableListener接口，并在onFrameAvailable回调中请求每一帧数据进行渲染，也就是说Camera的预览需要我们自己绘制完成
3. GLSurfaceView提供了绘制接口Renderer,我们需要定义CameraSurfaceRenderer实现该接口，并在GLSurfaceView初始化时设置自定义的渲染类。在onSurfaceCreated回调中创建外部纹理SurfaceTexture，并设置OnFrameAvailableListener监听Camera数据回调
4. 实现自定义CameraCallback接口，监听Camera状态
5. 一定要实现onResume和onPause接口，并在对应的Activity生命周期中调用。这是所有使用Camera的bug的源头

java
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public class CameraGLSurfaceView extends GLSurfaceView implements SurfaceTexture.OnFrameAvailableListener, CameraCallback {

    private static final String TAG = CameraGLSurfaceView.class.getSimpleName();

    private Context mContext;
    private SurfaceTexture mSurfaceTexture;
    private CameraHandler mCameraHandler;
    private boolean hasSurface; // 是否存在摄像头显示层
    private CameraManager mCameraManager;
    private int mRatioWidth = 0;
    private int mRatioHeight = 0;
    private int mGLSurfaceWidth;
    private int mGLSurfaceHeight;
    private CameraSurfaceRenderer mRenderer;

    public CameraGLSurfaceView(Context context) {
        super(context);
        init(context);
    }

    public CameraGLSurfaceView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init(context);
    }

    private void init(Context context) {
        mContext = context;
        mCameraHandler = new CameraHandler(this);

        mCameraManager = new CameraManager(context);
        mCameraManager.setCameraCallback(this);

        setEGLContextClientVersion(2);
        mRenderer = new CameraSurfaceRenderer(mCameraHandler);
        setRenderer(mRenderer);
        setRenderMode(GLSurfaceView.RENDERMODE_WHEN_DIRTY);
    }

    public SurfaceTexture getSurfaceTexture() {
        return mSurfaceTexture;
    }

    private void setAspectRatio(int width, int height) {
        if (width < 0 || height < 0) {
            throw new IllegalArgumentException("Size cannot be negative.");
        }
        mRatioWidth = width;
        mRatioHeight = height;
        requestLayout();
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        int width = MeasureSpec.getSize(widthMeasureSpec);
        int height = MeasureSpec.getSize(heightMeasureSpec);
        if (0 == mRatioWidth || 0 == mRatioHeight) {
            setMeasuredDimension(width, height);
        } else {
            if (width < height * mRatioWidth / mRatioHeight) {
                setMeasuredDimension(width, width * mRatioHeight / mRatioWidth);
            } else {
                setMeasuredDimension(height * mRatioWidth / mRatioHeight, height);
            }
        }
    }

    @Override
    public void onFrameAvailable(SurfaceTexture surfaceTexture) {
        requestRender();
    }

    /**
     * Connects the SurfaceTexture to the Camera preview output, and starts the preview.
     */
    private void handleSetSurfaceTexture(SurfaceTexture st) {
        Logs.i(TAG, "handleSetSurfaceTexture.");
        mSurfaceTexture = st;
        hasSurface = true;
        mSurfaceTexture.setOnFrameAvailableListener(this);
        openCamera();
    }

    /**
     *
     * @param width
     * @param height
     */
    private void handleSurfaceChanged(int width, int height) {
        Logs.i(TAG, "handleSurfaceChanged.");
        mGLSurfaceWidth = width;
        mGLSurfaceHeight = height;
        setAspectRatio();
    }

    /**
     * 打开摄像头并预览
     */
    public void onResume() {
        super.onResume();
        if (hasSurface) {
            // 当activity暂停，但是并未停止的时候，surface仍然存在，所以 surfaceCreated()
            // 并不会调用，需要在此处初始化摄像头
            openCamera();
        }
    }

    /**
     * 停止预览并关闭摄像头
     */
    public void onPause() {
        super.onPause();
        closeCamera();
    }

    public void onDestroy() {
        mCameraHandler.invalidateHandler();
    }

    /**
     * 打开摄像头
     */
    private void openCamera() {
        if (mSurfaceTexture == null) {
            Logs.e(TAG, "mSurfaceTexture is null.");
            return;
        }
        if (mCameraManager.isOpen()) {
            Logs.w(TAG, "Camera is opened！");
            return;
        }
        mCameraManager.openCamera();
        if (mCameraManager.isOpen()) {
            mCameraManager.startPreview(mSurfaceTexture);
        }
    }

    private void closeCamera() {
        mCameraManager.releaseCamera();
        queueEvent(() -> mRenderer.notifyPausing());
        mSurfaceTexture = null;
    }

    @Override
    public void onOpen() {

    }

    @Override
    public void onOpenError(int error, String msg) {

    }

    @Override
    public void onPreview(int previewWidth, int previewHeight) {
        Logs.i(TAG, "onPreview " + previewWidth + " " + previewHeight);
        queueEvent(() -> mRenderer.setCameraPreviewSize(previewWidth, previewHeight));
        setAspectRatio();
    }

    @Override
    public void onPreviewError(int error, String msg) {

    }

    @Override
    public void onClose() {

    }

    private void setAspectRatio() {
        int previewWidth = mCameraManager.getPreviewWidth();
        int previewHeight = mCameraManager.getPreviewHeight();
        if (mGLSurfaceWidth > mGLSurfaceHeight) {
            setAspectRatio(previewWidth, previewHeight);
        } else {
            setAspectRatio(previewHeight, previewWidth);
        }
    }

    /**
     * Handles camera operation requests from other threads.  Necessary because the Camera
     * must only be accessed from one thread.
     * 

     * The object is created on the UI thread, and all handlers run there.  Messages are
     * sent from other threads, using sendMessage().
     */
    static class CameraHandler extends Handler {
        public static final int MSG_SET_SURFACE_TEXTURE = 0;

        public static final int MSG_SURFACE_CHANGED = 1;

        private WeakReference mWeakGLSurfaceView;

        public CameraHandler(CameraGLSurfaceView view) {
            mWeakGLSurfaceView = new WeakReference<>(view);
        }

        /**
         * Drop the reference to the activity.  Useful as a paranoid measure to ensure that
         * attempts to access a stale Activity through a handler are caught.
         */
        public void invalidateHandler() {
            mWeakGLSurfaceView.clear();
        }

        @Override
        public void handleMessage(@NonNull Message msg) {
            super.handleMessage(msg);
            int what = msg.what;

            CameraGLSurfaceView view = mWeakGLSurfaceView.get();
            if (view == null) {
                return;
            }

            switch (what) {
                case MSG_SET_SURFACE_TEXTURE:
                    view.handleSetSurfaceTexture((SurfaceTexture) msg.obj);
                    break;
                case MSG_SURFACE_CHANGED:
                    view.handleSurfaceChanged(msg.arg1, msg.arg2);
                    break;
                default:
                    throw new RuntimeException("unknown msg " + what);
            }
        }
    }

    /**
     * Renderer object for our GLSurfaceView.
     * 

     * Do not call any methods here directly from another thread -- use the
     * GLSurfaceView#queueEvent() call.
     */
    static class CameraSurfaceRenderer implements GLSurfaceView.Renderer {

        private CameraGLSurfaceView.CameraHandler mCameraHandler;

        private final float[] mDisplayProjectionMatrix = new float[16];
        private CameraFilter mCameraFilter;
        // width/height of the incoming camera preview frames
        private boolean mSizeUpdated;
        private int mCameraPreviewWidth;
        private int mCameraPreviewHeight;
        private int mTextureId;
        private SurfaceTexture mSurfaceTexture;

        public CameraSurfaceRenderer(CameraGLSurfaceView.CameraHandler cameraHandler) {
            mCameraHandler = cameraHandler;

            mTextureId = -1;

            mSizeUpdated = false;
            mCameraPreviewWidth = mCameraPreviewHeight = -1;
            mCameraFilter = new CameraFilter();
        }

        /**
         * Notifies the renderer thread that the activity is pausing.
         * 

         * For best results, call this *after* disabling Camera preview.
         */
        public void notifyPausing() {
            if (mSurfaceTexture != null) {
                Logs.d(TAG, "renderer pausing -- releasing SurfaceTexture");
                mSurfaceTexture.release();
                mSurfaceTexture = null;
            }
            if (mCameraFilter != null) {
                mCameraFilter.release();     // assume the GLSurfaceView EGL context is about
            }
            mCameraPreviewWidth = mCameraPreviewHeight = -1;
        }

        @Override
        public void onSurfaceCreated(GL10 gl, EGLConfig config) {
            Logs.i(TAG, "onSurfaceCreated. " + Thread.currentThread().getName());
            mTextureId = GLESUtils.createOESTexture();
            mCameraFilter.surfaceCreated();

            // Create a SurfaceTexture, with an external texture, in this EGL context.  We don't
            // have a Looper in this thread -- GLSurfaceView doesn't create one -- so the frame
            // available messages will arrive on the main thread.
            mSurfaceTexture = new SurfaceTexture(mTextureId);

            mCameraHandler.sendMessage(mCameraHandler.obtainMessage(CameraHandler.MSG_SET_SURFACE_TEXTURE, mSurfaceTexture));
        }

        @Override
        public void onSurfaceChanged(GL10 gl, int width, int height) {
            mCameraFilter.surfaceChanged(width, height);
            mCameraHandler.sendMessage(mCameraHandler.obtainMessage(CameraHandler.MSG_SURFACE_CHANGED, width, height));
        }

        @Override
        public void onDrawFrame(GL10 gl) {
            if (mSurfaceTexture == null) return;

            // 把摄像头的数据先输出来
            // 更新纹理，然后我们才能够使用opengl从SurfaceTexture当中获得数据 进行渲染
            mSurfaceTexture.updateTexImage();

            if (mCameraPreviewWidth <= 0 || mCameraPreviewHeight <= 0) {
                return;
            }
            if (mSizeUpdated) {
                mSizeUpdated = false;
            }

            mSurfaceTexture.getTransformMatrix(mDisplayProjectionMatrix);
            mCameraFilter.draw(mTextureId, mDisplayProjectionMatrix);
        }

        public void setCameraPreviewSize(int width, int height) {
            mCameraPreviewWidth = width;
            mCameraPreviewHeight = height;
            mSizeUpdated = true;
        }
    }
}

1.Camera操作时机

与SurfaceView和TextureView不同，GLSurfaceView中并没有地方获取SurfaceTexture的地方，虽然Renderer接口有onSurfaceCreated回调但是并没有SurfaceTexture，而是要求我们自己创建外部纹理ID用于Camera预览数据的回调。至于这个外部纹理如何又显示到GLSurfaceView上的，这个章节就不先介绍了，后续我们进行完整的opengl环境搭建再进一步讨论。

Renderer中的所有回调接口都是运行在独立的线程中的，这也就是为什么我们要单独定义个类，而不是让CameraGLSurfaceView直接实现该接口，让他和别的接口方法隔离

GLSurfaceView中setRenderer接口源码可以看到会启动一个GLThread线程，Renderer接口都是运行在该线程中

java
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    public void setRenderer(Renderer renderer) {
        ...
        mRenderer = renderer;
        mGLThread = new GLThread(mThisWeakRef);
        mGLThread.start();
    }

因此我们要把创建好的外部纹理通过Handler传递给UI线程，UI线程在获取到SurfaceTexture后打开摄像头，记得在onResume中也同样打开一次摄像头

java
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        @Override
        public void onSurfaceCreated(GL10 gl, EGLConfig config) {
            // 创建外部纹理ID
            mTextureId = GLESUtils.createOESTexture();
            // 着色器程序执行相应的方法
            mCameraFilter.surfaceCreated();
            // 在此EGL上下文中创建具有外部纹理的SurfaceTexture
            mSurfaceTexture = new SurfaceTexture(mTextureId);
            // 将SurfaceTexture传递给UI线程
            mCameraHandler.sendMessage(mCameraHandler.obtainMessage(CameraHandler.MSG_SET_SURFACE_TEXTURE, mSurfaceTexture));
        }

我们重写surfaceDestroyed，在该回调和onPause中关闭摄像头

注意surfaceDestroyed是SurfaceHolder.Callback的方法，该方法是运行在UI线程中的

2. GLSurfaceView计算大小

1. 和SurfaceView和TextureView一样，我们在onPreview回调中设置TextureView的大小和比例
2. 在onSurfaceChanged回调中设置GL画布大小，调用着色器生对应方法，着色器的surfaceChanged方法中设置画布大小，偶发预览变形大多是没有在此调用glViewport方法导致

java
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        @Override
        public void onSurfaceChanged(GL10 gl, int width, int height) {
            mCameraFilter.surfaceChanged(width, height);
            mCameraHandler.sendMessage(mCameraHandler.obtainMessage(CameraHandler.MSG_SURFACE_CHANGED, width, height));
        }

二.最后

本文介绍了Camera+GLSurfaceView的基本操作及关键代码。本章内容也不是很多，介绍了如何用GLSurfaceView预览Camera数据的流程。我们没有对opengl的API进行过多的讲解，以及Renderer接口是如何将数据渲染到GLSurfaceView中的。在后续的章节我会讲解opengl在Android中的使用，希望聪明的你在回看该章会有种醍醐灌顶的感觉吧。

lib-camera库包结构如下：

每个包都可独立使用做到最低的耦合，方便白嫖

github地址：github.com/xiaozhi003/…，如果对你有帮助可以star下，万分感谢^_^

参考：

1. github.com/afei-cn/Cam…
2. github.com/saki4510t/U…
3. github.com/google/graf…