相信很多人都用过相机功能，也开发过简单调度相机功能，但是相机采集功能。是图像信号输入的重要来源。

SurfaceView和View的不同之处：

相机图像采样，需要维持一个比较稳定的帧数来维持图像实时性，需要频繁刷新，创建一个子线程来进行画面更新，会被占用主线程效率好很多，而且双缓冲机制可以在画面从前台刷新到后台时才占用主线程操作，所以选用SurfaceView作绘制是最好的。 而GLSurfaceView是SurfaceView的一个子类，专用于openGL绘制，其运行效率远高于SurfaceView是因为使用了GPU参与绘制。 这一节介绍Android摄像头采样，还是采用了SurfaceView来做采样 1.需要申请相机权限。

    <uses-permission android:name="android.permission.CAMERA" />
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2.打开摄像头，先检查摄像和前置摄像头，然后通过摄像头Id，来返回摄像头对象。

 fun openCamera(cameraId:Int):Camera?{if (!haveFeature(PackageManager.FEATURE_CAMERA)){Log.e(TAG,"no camera!")return null}if (cameraId == Camera.CameraInfo.CAMERA_FACING_FRONT && !haveFeature(PackageManager.FEATURE_CAMERA_FRONT)){Log.e(TAG,"no front camera!")return null}val camera = Camera.open(cameraId)if (camera == null){Log.e(TAG, "openCamera failed")return null}return camera}
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3.设置画面比例

/*** 获取最大的图片大小*/fun getLargePictureSize(camera: Camera?): Camera.Size? {if (camera != null) {//获取可选比例val sizes = camera.parameters.supportedPictureSizesvar temp: Camera.Size = sizes[0]for (i in 1 until sizes.size) {val scale = sizes[i].height.toFloat() / sizes[i].widthif (temp.width < sizes[i].width && scale < 0.6f && scale > 0.5f)temp = sizes[i]}return temp}return null}/*** 获取最大的预览大小*/fun getLargePreviewSize(camera: Camera?): Camera.Size? {if (camera != null) {//获取可选比例val sizes = camera.parameters.supportedPreviewSizesvar temp: Camera.Size = sizes[0]for (i in 1 until sizes.size) {if (temp.width < sizes[i].width)temp = sizes[i]}return temp}return null}/*** 相机采样参数大小*/fun setOptimalSize(camera:Camera,aspectRatio:Float,maxWidth:Int,maxHeight:Int){val parameters= camera.parameters//使用自动对焦if (parameters.supportedFocusModes.contains(Camera.Parameters.FOCUS_MODE_CONTINUOUS_PICTURE)) {parameters.focusMode = Camera.Parameters.FOCUS_MODE_CONTINUOUS_PICTURE}val size = getLargePreviewSize(camera)size?.let {//设置相机预览大小parameters.setPreviewSize(it.width,it.height)Log.d(TAG, "input max: (" + maxWidth + ", " + maxHeight + "), output size: ("+ it.width + ", " + it.height + ")")}val pictureSize = getLargePictureSize(camera)pictureSize?.let {//图片参数parameters.setPictureSize(it.width,it.height)Log.d(TAG, "picture max: (" + maxWidth + ", " + maxHeight + "), output size: ("+ it.width + ", " + it.height + ")")}camera.parameters = parameters}
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3.设置相机图像角度

fun setDisplayOritation(activity: Activity, camera: Camera, cameraId: Int) {//获取window的角度val rotation = activity.windowManager.defaultDisplay.rotationvar degress = 0when (rotation) {Surface.ROTATION_0 -> degress = 0Surface.ROTATION_90 -> degress = 90Surface.ROTATION_180 -> degress = 180Surface.ROTATION_270 -> degress = 270}val info = Camera.CameraInfo()Camera.getCameraInfo(cameraId, info)var result: Int//前置摄像头if (info.facing == Camera.CameraInfo.CAMERA_FACING_FRONT) {result = (info.orientation + degress) % 360result = (360 - result) % 360  // compensate the mirror} else {//后置摄像头result = (info.orientation - degress + 360) % 360 // back-facing}Log.d(TAG, "window rotation: $degress, camera oritation: $result")camera.setDisplayOrientation(result)}
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4.设置完摄像头参数后，需要设置一个SurfaceHolder.CallBack。 有三个必须的方法

   //创建时调用override fun surfaceCreated(holder: SurfaceHolder?) { }//当surface发生任何结构性的变化时（格式或者大小），该方法就会被立即调用。override fun surfaceChanged(holder: SurfaceHolder?, format: Int, width: Int, height: Int) { }//被移除时调用override fun surfaceDestroyed(holder: SurfaceHolder?) {}
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这里创建相机的调用surfaceCreated，之后会立刻调用一次surfaceChanged 这里在surfaceChanged上调用openGL的init操作

 fun initOpenGL(surface: Surface, width: Int, height: Int){//新开一个之后一个线程的线程池mExecutor.execute {//获取纹理idval textureId = OpenGLJniLib.magicBaseInit(surface,width,height,BaseApplication.context.assets)if (textureId < 0){Log.e(TAG, "surfaceCreated init OpenGL ES failed!")return@execute}//需要使用surfaceTexture来做纹理装载mSurfaceTexture = SurfaceTexture(textureId)//添加纹理变化回调mSurfaceTexture?.setOnFrameAvailableListener { drawOpenGL() }try {//把摄像头采样关联到纹理mCamera?.setPreviewTexture(mSurfaceTexture)//开始摄像头采样doStartPreview()}catch (e:IOException){Log.e(TAG,e.localizedMessage)releaseOpenGL()}}}
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5.开始预览，并开始自动对焦。

    fun doStartPreview(){mCamera?.startPreview()cameraFocus(width/2.0f,height/2.0f)}
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6.opengl绘制，先要强制更新纹理图像，再更新获取纹理矩阵，然后让opengl绘制

    fun drawOpenGL(){mExecutor.execute {mSurfaceTexture?.updateTexImage()mSurfaceTexture?.getTransformMatrix(mMatrix)OpenGLJniLib.magicBaseDraw(mMatrix)}}
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7.在destroySurfaceView的是否释放资源

    fun releaseOpenGL(){mExecutor.execute {mSurfaceTexture?.release()mSurfaceTexture=nullOpenGLJniLib.magicBaseRelease()}}
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介绍了Camera采样配置和，surfaceTexture纹理获取了和加载，下一节，将会介绍native层的opengl绘制代码。

近来在写一个有趣的项目，大家熟知摄像头绘制和opengl的人应该有看过MagicCamera这个Android opengl2.0的开源工程，但是已经很多年没人维护了，这边正在将其重构为opengl3.0的的版本。命名为MagicCamera3以供大家学习，现在还在重构当中，致敬作者，也希望可以有机会和作者多交流，如果有认识的可以告知我一声，谢谢。 开源地址：MagicCamera3，这节的用例在CameraActivity中