初识：Android中使用OpenGL预览Camera【摄像头】画面

一. 本文你将了解到：

自定义属于自己的SurfaceView，自定义EGLHelper 共享EGLContext, 效仿GLSurfaceView来做。【这么做的目的是为将来多个Surface 渲染同一个纹理做提前准备】
通过Render渲染器使用VBO FBO 投影矩阵实现 “离屏渲染” 【离屏渲染主要使用FBO】
摄像头旋转不同角度，通过矩阵变换使图像也跟着旋转。

二. 前期准备工作：

1.准备OpenGL 要是用的shader.glsl文件，仔细对比Camera用的着色器和离屏渲染用的着色器存在差异。
vertex_shader_camera.glsl 顶点着色器

attribute vec4 v_Position;
attribute vec2 f_Position;
varying vec2 ft_Position;
uniform mat4 u_Matrix;  
void main() {
    ft_Position = f_Position;
    gl_Position = v_Position * u_Matrix;
}

fragment_shader_camera.glsl 片元着色器

#extension GL_OES_EGL_image_external : require  
precision mediump float;
varying vec2 ft_Position;
uniform samplerExternalOES sTexture;
void main() {
    gl_FragColor=texture2D(sTexture, ft_Position);
}

vertex_shader_fbo.glsl 离屏渲染用到的顶点着色器

attribute vec4 v_Position;
attribute vec2 f_Position;
varying vec2 ft_Position;
void main() {
    ft_Position = f_Position;
    gl_Position = v_Position;
}

fragment_shader_fbo.glsl 离屏渲染用到的片元着色器

precision mediump float;
varying vec2 ft_Position;
uniform sampler2D sTexture;
void main() {
    gl_FragColor=texture2D(sTexture, ft_Position);
}

模仿Android提供的GLSurfaceView 实现一个我们自己的SurfaceView
首先：自定义一个EGLHelper管理EGL环境【BaseEglHelper.java】
其次：自定义抽象类BaseSurfaceView 继承SurfaceView 实现 SurfaceHolder.Callback 【BaseSurfaceView它能把EGLContext共享给其他Surface，但是Android_GLSurfaceView不能共享EGLContext】
最后：CameraRender 实现BaseSurfaceView.GLRender 来搞出自己的渲染类【CameraRender.java】
由于代码相对较多，此处不贴出代码，文末将给出代码地址
提供一个用于离屏渲染的Render 【CameraFboRender.java】
定义相机类，用来搞开始渲染，停止渲染，释放资源，切换摄像头等

三. 实战使用自定义的BaseSurfaceView 实现预览Camera图像

public class CameraView extends BaseSurfaceView {

    private AnCamera camera; //自己的摄像头类
    private CameraRender cameraRender; //渲染类
    private int cameraId = Camera.CameraInfo.CAMERA_FACING_BACK;//后置摄像头

    public CameraView(Context context) {
        this(context, null);
    }

    public CameraView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public CameraView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init(context);
    }


    private void init(Context context) {
        camera = new AnCamera(context);
        cameraRender = new CameraRender(context);
        setRender(cameraRender);
        switchPreAngle(context);
        cameraRender.setOnSurfaceTextureListener(new CameraRender.onSurfaceTextureListener() {
            @Override
            public void onCreateSurfaceTexture(SurfaceTexture surfaceTexture) {
                camera.initCamera(surfaceTexture, cameraId);
            }
        });
    }

    //停止预览
    public void onDestroy() {
        if (camera != null) {
            camera.setStopCamera();
        }
    }

    //切换屏幕预览角度
    public void switchPreAngle(Context context) {
        int angle = 0;
        WindowManager manager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
        if (manager != null) {
            angle = manager.getDefaultDisplay().getRotation();
        }
        cameraRender.resetMatrix();
        switch (angle) {
            case Surface.ROTATION_0:
                Log.d("CameraView", "0");
                if (cameraId == Camera.CameraInfo.CAMERA_FACING_BACK) {
                    cameraRender.setAngle(90, 0, 0, 1);
                    cameraRender.setAngle(180, 1, 0, 0);
                } else {
                    cameraRender.setAngle(90f, 0f, 0f, 1f);
                }

                break;
            case Surface.ROTATION_90:
                Log.d("CameraView", "90");
                if (cameraId == Camera.CameraInfo.CAMERA_FACING_BACK) {
                    cameraRender.setAngle(180, 0, 0, 1);
                    cameraRender.setAngle(180, 0, 1, 0);
                } else {
                    cameraRender.setAngle(90f, 0f, 0f, 1f);
                }
                break;
            case Surface.ROTATION_180:
                Log.d("CameraView", "180");
                if (cameraId == Camera.CameraInfo.CAMERA_FACING_BACK) {
                    cameraRender.setAngle(90f, 0.0f, 0f, 1f);
                    cameraRender.setAngle(180f, 0.0f, 1f, 0f);
                } else {
                    cameraRender.setAngle(-90, 0f, 0f, 1f);
                }
                break;
            case Surface.ROTATION_270:
                Log.d("CameraView", "270");
                if (cameraId == Camera.CameraInfo.CAMERA_FACING_BACK) {
                    cameraRender.setAngle(180f, 0.0f, 1f, 0f);
                } else {
                    cameraRender.setAngle(0f, 0f, 0f, 1f);
                }
                break;
        }
    }
}

布局文件 main_layout.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="activity.MainActivity">

    <camera1.CameraView
        android:id="@+id/camera_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</FrameLayout>

主页面 MainActivity.java 【记得别忘加权限】

public class MainActivity extends AppCompatActivity {

    /*权限请求Code*/
    private final static int PERMISSION_REQUEST_CODE = 1234;
    /*我们需要使用的权限*/
    private String[] permissions = {
            Manifest.permission.WRITE_EXTERNAL_STORAGE,
            Manifest.permission.READ_EXTERNAL_STORAGE,
            Manifest.permission.CAMERA,
            Manifest.permission.RECORD_AUDIO
    };

    private CameraView cameraView;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        /*SDK>6.0 权限申请*/
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M &&
                checkSelfPermission(permissions[0]) != PackageManager.PERMISSION_GRANTED &&
                checkSelfPermission(permissions[1]) != PackageManager.PERMISSION_GRANTED &&
                checkSelfPermission(permissions[2]) != PackageManager.PERMISSION_GRANTED &&
                checkSelfPermission(permissions[3]) != PackageManager.PERMISSION_GRANTED) {
            requestPermissions(permissions, PERMISSION_REQUEST_CODE);
        }
        cameraView = findViewById(R.id.camera_view);
    }

    @Override
    public void onConfigurationChanged(Configuration newConfig) {
        super.onConfigurationChanged(newConfig);
        cameraView.switchPreAngle(MainActivity.this);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        cameraView.onDestroy();
    }

    //权限反馈
    @Override
    public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
        switch (requestCode) {
            case PERMISSION_REQUEST_CODE:
                /*PackageManager.PERMISSION_GRANTED  权限被许可*/
                /*PackageManager.PERMISSION_DENIED  没有权限；拒绝访问*/
                if (grantResults.length > 0 && grantResults[0] != PackageManager.PERMISSION_GRANTED) {
                    showWaringDialog("无法读取内存卡！");
                } else if (grantResults.length > 0 && grantResults[1] != PackageManager.PERMISSION_GRANTED) {
                    showWaringDialog("无法读取内存卡！");
                } else if (grantResults.length > 0 && grantResults[2] != PackageManager.PERMISSION_GRANTED) {
                    showWaringDialog("无法使用相机！");
                } else if (grantResults.length > 0 && grantResults[3] != PackageManager.PERMISSION_GRANTED) {
                    showWaringDialog("无法录制音频！");
                }
                break;
        }
    }

    private void showWaringDialog(String msg) {
        AlertDialog dialog = new AlertDialog.Builder(this)
                .setTitle("警告！")
                .setMessage(msg)
                .setPositiveButton(R.string.ok, new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        // 一般情况下如果用户不授权的话，功能是无法运行的，我们暂时做退出处理
                        finish();
                    }
                }).setPositiveButton(R.string.cancel, new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        // 一般情况下如果用户不授权的话，功能是无法运行的，我们暂时做退出处理
                        finish();
                    }
                }).show();
    }
}

代码地址【位于antony_live module中】：https://github.com/YuLingRui/AntonyLLTV.git