当我们需要把同一个场景渲染到不同的Surface上时，此时系统GLSurfaceView 就不能满足需求了，所以我们需要自己创建EGL环境来实现渲染操作。
注意: OpenGL整体是一个状态机，通过改变状态就能改变后续的渲染方式，而 EGLContext（EgL上下文）就保存有所有状态，因此可以通过共享EGLContext 来实现同一场景渲染到不同的Surface上。

我们通过分析GLSurfaceView来实现自己的代码

GLSurfaceView

首先需要配置EGL环境(EGLHelper)：Android配置EGL环境

EGL环境配置成功后，定义GLSurfaceView主要为以下步骤：

1、继成SurfaceView，并实现其CallBack回调
2、自定义GLThread线程类，主要用于OpenGL的绘制操作
3、添加设置Surface和EglContext的方法
4、提供和系统GLSurfaceView相同的调用方法

EglSurfaceView.java

package com.zzw.glsurfaceviewdemo;

import android.content.Context;
import android.util.AttributeSet;
import android.view.Surface;
import android.view.SurfaceHolder;
import android.view.SurfaceView;

import java.lang.ref.WeakReference;

import javax.microedition.khronos.egl.EGLContext;

public class EglSurfaceView extends SurfaceView implements SurfaceHolder.Callback {

    private Renderer mRenderer;
    private EGLThread mEGLThread;
    private Surface mSurface;
    private EGLContext mEglContext;


    public final static int RENDERMODE_WHEN_DIRTY = 0;
    public final static int RENDERMODE_CONTINUOUSLY = 1;
    private  int mRenderMode = RENDERMODE_CONTINUOUSLY;



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

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

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

    private void init() {
        SurfaceHolder holder = getHolder();
        holder.addCallback(this);
    }


    @Override
    public void surfaceCreated(SurfaceHolder holder) {
        if (mSurface == null) {
            mSurface = holder.getSurface();
        }
        mEGLThread = new EGLThread(new WeakReference<>(this));
        mEGLThread.isCreate = true;
        mEGLThread.start();
    }

    @Override
    public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
        mEGLThread.width = width;
        mEGLThread.height = height;
        mEGLThread.isChange = true;
    }

    @Override
    public void surfaceDestroyed(SurfaceHolder holder) {
        mEGLThread.onDestroy();
        mEGLThread = null;
        mSurface = null;
        mEglContext = null;
    }

    public void setRenderer(Renderer mRenderer) {
        this.mRenderer = mRenderer;
    }

    public void setRenderMode(int renderMode) {
        if (mRenderer == null) {
            throw new RuntimeException("must set render before");
        }
        this.mRenderMode =renderMode;
    }

    public void requestRender() {
        if (mEGLThread != null) {
            mEGLThread.requestRender();
        }
    }

    public void setSurfaceAndEglContext(Surface surface, EGLContext eglContext) {
        this.mSurface = surface;
        this.mEglContext = eglContext;
    }

    public EGLContext getEglContext() {
        if (mEGLThread != null) {
            return mEGLThread.getEglContext();
        }
        return null;
    }


    private static class EGLThread extends Thread {


        EGLThread(WeakReference<EglSurfaceView> eGLSurfaceViewWeakRef) {
            this.mEGLSurfaceViewWeakRef = eGLSurfaceViewWeakRef;
        }

        @Override
        public void run() {
            super.run();
            try {
                guardedRun();
            } catch (Exception e) {
                // fall thru and exit normally
            }
        }

        private void guardedRun() throws InterruptedException {
            isExit = false;
            isStart = false;
            object = new Object();
            mEglHelper = new EglHelper();
            mEglHelper.initEgl(mEGLSurfaceViewWeakRef.get().mSurface, mEGLSurfaceViewWeakRef.get().mEglContext);

            while (true) {
                if (isExit) {
                    //释放资源
                    release();
                    break;
                }

                if (isStart) {
                    if (mEGLSurfaceViewWeakRef.get().mRenderMode == RENDERMODE_WHEN_DIRTY) {
                        synchronized (object) {
                            object.wait();
                        }
                    } else if (mEGLSurfaceViewWeakRef.get().mRenderMode == RENDERMODE_CONTINUOUSLY) {
                        Thread.sleep(1000 / 60);
                    } else {
                        throw new IllegalArgumentException("renderMode");
                    }
                }

                onCreate();
                onChange(width, height);
                onDraw();
                isStart = true;
            }

        }

        private void onCreate() {
            if (!isCreate || mEGLSurfaceViewWeakRef.get().mRenderer == null)
                return;

            isCreate = false;
            mEGLSurfaceViewWeakRef.get().mRenderer.onSurfaceCreated();
        }

        private void onChange(int width, int height) {
            if (!isChange || mEGLSurfaceViewWeakRef.get().mRenderer == null)
                return;

            isChange = false;
            mEGLSurfaceViewWeakRef.get().mRenderer.onSurfaceChanged(width, height);
        }

        private void onDraw() {
            if (mEGLSurfaceViewWeakRef.get().mRenderer == null)
                return;

            mEGLSurfaceViewWeakRef.get().mRenderer.onDrawFrame();
            //第一次的时候手动调用一次 不然不会显示ui
            if (!isStart) {
                mEGLSurfaceViewWeakRef.get().mRenderer.onDrawFrame();
            }

            mEglHelper.swapBuffers();
        }

        void requestRender() {
            if (object != null) {
                synchronized (object) {
                    object.notifyAll();
                }
            }
        }

        void onDestroy() {
            isExit = true;
            //释放锁
            requestRender();
        }

        void release() {
            if (mEglHelper != null) {
                mEglHelper.destoryEgl();
                mEglHelper = null;
                object = null;
                mEGLSurfaceViewWeakRef = null;
            }
        }

        EGLContext getEglContext() {
            if (mEglHelper != null) {
                return mEglHelper.getEglContext();
            }
            return null;
        }

        private WeakReference<EglSurfaceView> mEGLSurfaceViewWeakRef;
        private EglHelper mEglHelper;

        private int width;
        private int height;

        private boolean isCreate;
        private boolean isChange;
        private boolean isStart;
        private boolean isExit;

        private Object object;
    }


    interface Renderer {
        void onSurfaceCreated();

        void onSurfaceChanged(int width, int height);

        void onDrawFrame();

    }
}

使用和正常的GLSurfaceView一样:

package com.zzw.glsurfaceviewdemo;

import android.opengl.GLES20;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;

public class MainActivity extends AppCompatActivity implements EglSurfaceView.Renderer {

    private EglSurfaceView eglSurfaceView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        eglSurfaceView = findViewById(R.id.egl_surface_view);

        eglSurfaceView = new EglSurfaceView(this);
        eglSurfaceView.setRenderer(this);
//        eglSurfaceView.setRenderMode(EglSurfaceView.RENDERMODE_CONTINUOUSLY);

        eglSurfaceView.setRenderMode(EglSurfaceView.RENDERMODE_WHEN_DIRTY);
        eglSurfaceView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                eglSurfaceView.requestRender();
            }
        });
        setContentView(eglSurfaceView);
    }

    @Override
    public void onSurfaceCreated() {
        Log.e("zzz", "onSurfaceCreated");
    }

    @Override
    public void onSurfaceChanged(int width, int height) {
        Log.e("zzz", "onSurfaceChanged");
        GLES20.glViewport(0, 0, width, height);
    }

    @Override
    public void onDrawFrame() {
        Log.e("zzz", "onDrawFrame");
        GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT);
        GLES20.glClearColor(1.0f, 0.0f, 1.0f, 1.0f);
    }
}