之前写过全景（VR）图片，和用openGL ES+MediaPlayer 渲染播放视频+滤镜效果

这一篇就在之前的基础上实现一个最简单的VR播放器，播放全景视频。

概述：

全景视频是一种用3D摄像机进行全方位360度进行拍摄的视频，用户在观看视频的时候，可以随意调节视频上下左右进行观看。

展示：

“身临其境的枪战” 可见晃动手机，视图也跟着转！

这里写图片描述

原理：

1.用OpenGL绘制一个球。
2.MediaPlayer 播放的视频纹理贴到球上（可以想象为一个地球仪）。
3.把观测点设置在求内部。 （想象为从球内部中心点观看球的表面）。
4.用手机内置的传感器得到一个手机移动的矩阵（视频画面就可以随着手机的移动而移动了）。

实践：

1.用OpenGL绘制一个球
效果如图：

这里写图片描述

用OpenGL绘制任何图形，都需要先知道顶点坐标。然后用GLES20.glDrawArrays绘制出来。
那么绘制一个球体，可以想象为无数个三角形在三维空间构成。
下面这个算法就会放回一个球体的坐标数组

 private float[] createBallPos(){
        //球以(0,0,0)为中心，以R为半径，则球上任意一点的坐标为
        // ( R * cos(a) * sin(b),y0 = R * sin(a),R * cos(a) * cos(b))
        // 其中，a为圆心到点的线段与xz平面的夹角，b为圆心到点的线段在xz平面的投影与z轴的夹角
        ArrayList<Float> data=new ArrayList<>();
        float r1,r2;
        float h1,h2;
        float sin,cos;
        for(float i=-90;i<90+step;i+=step){
            r1 = (float)Math.cos(i * Math.PI / 180.0);
            r2 = (float)Math.cos((i + step) * Math.PI / 180.0);
            h1 = (float)Math.sin(i * Math.PI / 180.0);
            h2 = (float)Math.sin((i + step) * Math.PI / 180.0);
            // 固定纬度, 360 度旋转遍历一条纬线
            float step2=step*2;
            for (float j = 0.0f; j <360.0f+step; j +=step2 ) {
                cos = (float) Math.cos(j * Math.PI / 180.0);
                sin = -(float) Math.sin(j * Math.PI / 180.0);

                data.add(r2 * cos);
                data.add(h2);
                data.add(r2 * sin);
                data.add(r1 * cos);
                data.add(h1);
                data.add(r1 * sin);
            }
        }
        float[] f=new float[data.size()];
        for(int i=0;i<f.length;i++){
            f[i]=data.get(i);
        }
        return f;
    }

然后把坐标传给natave层

  float[] dataPos=createBallPos();

        vertexBuffer = ByteBuffer.allocateDirect(dataPos.length * 4)
                .order(ByteOrder.nativeOrder())
                .asFloatBuffer()
                .put(dataPos);
        vertexBuffer.position(0);

        vSize=dataPos.length/3;

有了坐标就可以绘制球了。

2.MediaPlayer 播放的视频纹理贴到球上（可以想象为一个地球仪）。

先贴着色器代码

attribute vec4 aPosition;//顶点位置
attribute vec4 aTexCoord;//S T 纹理坐标
varying vec2 vTexCoord;
uniform mat4 uMatrix;
uniform mat4 uSTMatrix;

uniform mat4 uViewMatrix;
uniform mat4 uModelMatrix;
uniform mat4 uRotateMatrix;

void main() {
    vTexCoord = (uSTMatrix * aTexCoord).xy;
    gl_Position = uMatrix*uRotateMatrix*uViewMatrix*uModelMatrix*aPosition;
}

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

然后我们根据球的点把视频纹理贴到球上

        GLES20.glEnableVertexAttribArray(aPositionLocation);
        GLES20.glVertexAttribPointer(aPositionLocation, 3, GLES20.GL_FLOAT, false,
                0, posBuffer);
        GLES20.glEnableVertexAttribArray(aTextureCoordLocation);
        GLES20.glVertexAttribPointer(aTextureCoordLocation,2,GLES20.GL_FLOAT,false,0,cooBuffer);

绘制：

 GLES20.glDrawArrays(GLES20.GL_TRIANGLES, 0, vCount);

3.把观测点设置在求内部。 （想象为从球内部中心点观看球的表面）。

 //设置相机位置
        Matrix.setLookAtM(mViewMatrix, 0, 0f, 0.0f,0.0f, 0.0f, 0.0f,-1.0f, 0f,-1.0f, 0.0f);

4.用手机内置的传感器得到一个手机移动的矩阵（视频画面就可以随着手机的移动而移动了）
在activity中

 @Override
    public void onSensorChanged(SensorEvent sensorEvent) {
        SensorManager.getRotationMatrixFromVector(matrix,sensorEvent.values);
        glRenderer.setMatrix(matrix);
    }

VRVideoRenderer 完整代码如下：

import android.content.Context;
import android.graphics.SurfaceTexture;
import android.media.AudioManager;
import android.media.MediaPlayer;
import android.net.Uri;
import android.opengl.GLES11Ext;
import android.opengl.GLES20;
import android.opengl.GLSurfaceView;
import android.opengl.Matrix;
import android.util.Log;
import android.view.Surface;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.FloatBuffer;
import java.util.ArrayList;

import javax.microedition.khronos.egl.EGLConfig;
import javax.microedition.khronos.opengles.GL10;

/**
 * Created by Shuo.Wang on 2017/4/19.
 */

public class VRVideoRenderer implements GLSurfaceView.Renderer
        , SurfaceTexture.OnFrameAvailableListener, MediaPlayer.OnVideoSizeChangedListener  {


    private static final String TAG = "GLRenderer";
    
    private static final float UNIT_SIZE = 1f;// 单位尺寸
    private float radius=2f;

    final double angleSpan = Math.PI/90f;// 将球进行单位切分的角度
    int vCount = 0;// 顶点个数，先初始化为0
    private FloatBuffer posBuffer;
    private FloatBuffer cooBuffer;

    private int mHViewMatrix;
    private int mHModelMatrix;
    private int mHRotateMatrix;
    private float[] mViewMatrix=new float[16];
    private float[] mModelMatrix=new float[16];
    private float[] mRotateMatrix=new float[16];
    

    private Context context;
    private int aPositionLocation;
    private int programId;
    private FloatBuffer vertexBuffer;

    private final float[] projectionMatrix=new float[16];
    private int uMatrixLocation;

 
    private FloatBuffer textureVertexBuffer;
    private int uTextureSamplerLocation;
    private int aTextureCoordLocation;
    private int textureId;

    private SurfaceTexture surfaceTexture;
    private MediaPlayer mediaPlayer;
    private float[] mSTMatrix = new float[16];
    private int uSTMMatrixHandle;

    private boolean updateSurface;
    private boolean playerPrepared;
    private int screenWidth,screenHeight;
    public VRVideoRenderer(Context context, String videoPath) {
        this.context = context;
        playerPrepared=false;
        synchronized(this) {
            updateSurface = false;
        }
        calculateAttribute();

        mediaPlayer=new MediaPlayer();
        try{
            mediaPlayer.setDataSource(context, Uri.parse(videoPath));
        }catch (IOException e){
            e.printStackTrace();
        }
        mediaPlayer.setAudioStreamType(AudioManager.STREAM_MUSIC);
        mediaPlayer.setLooping(true);

        mediaPlayer.setOnVideoSizeChangedListener(this);
    }

    @Override
    public void onSurfaceCreated(GL10 gl, EGLConfig config) {
        String vertexShader = ShaderUtils.readRawTextFile(context, R.raw.simple_vertex_shader);
        String fragmentShader= ShaderUtils.readRawTextFile(context, R.raw.simple_fragment_shader);
        programId=ShaderUtils.createProgram(vertexShader,fragmentShader);
        aPositionLocation= GLES20.glGetAttribLocation(programId,"aPosition");

        uMatrixLocation=GLES20.glGetUniformLocation(programId,"uMatrix");
        uSTMMatrixHandle = GLES20.glGetUniformLocation(programId, "uSTMatrix");
        mHViewMatrix=GLES20.glGetUniformLocation(programId,"uViewMatrix");
        mHModelMatrix=GLES20.glGetUniformLocation(programId,"uModelMatrix");
        mHRotateMatrix=GLES20.glGetUniformLocation(programId,"uRotateMatrix");
        uTextureSamplerLocation=GLES20.glGetUniformLocation(programId,"sTexture");
        aTextureCoordLocation=GLES20.glGetAttribLocation(programId,"aTexCoord");


        int[] textures = new int[1];
        GLES20.glGenTextures(1, textures, 0);

        textureId = textures[0];
        GLES20.glBindTexture(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, textureId);
        ShaderUtils.checkGlError("glBindTexture mTextureID");
   /*GLES11Ext.GL_TEXTURE_EXTERNAL_OES的用处？
      之前提到视频解码的输出格式是YUV的（YUV420p，应该是），那么这个扩展纹理的作用就是实现YUV格式到RGB的自动转化，
      我们就不需要再为此写YUV转RGB的代码了*/
        GLES20.glTexParameterf(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, GLES20.GL_TEXTURE_MIN_FILTER,
                GLES20.GL_NEAREST);
        GLES20.glTexParameterf(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, GLES20.GL_TEXTURE_MAG_FILTER,
                GLES20.GL_LINEAR);

        surfaceTexture = new SurfaceTexture(textureId);
        surfaceTexture.setOnFrameAvailableListener(this);//监听是否有新的一帧数据到来

        Surface surface = new Surface(surfaceTexture);
        mediaPlayer.setSurface(surface);
        surface.release();

        if (!playerPrepared){
            try {
                mediaPlayer.prepare();
                playerPrepared=true;
            } catch (IOException t) {
                Log.e(TAG, "media player prepare failed");
            }
            mediaPlayer.start();
            playerPrepared=true;
        }
    }

    @Override
    public void onSurfaceChanged(GL10 gl, int width, int height) {
        Log.d(TAG, "onSurfaceChanged: "+width+" "+height);
        screenWidth=width; screenHeight=height;

        //计算宽高比
        float ratio=(float)width/height;
        //透视投影矩阵/视锥
        MatrixHelper.perspectiveM(projectionMatrix,0,90,ratio,1f,500);
        //设置相机位置
        Matrix.setLookAtM(mViewMatrix, 0, 0f, 0.0f,0.0f, 0.0f, 0.0f,-1.0f, 0f,-1.0f, 0.0f);
        //模型矩阵
        Matrix.setIdentityM(mModelMatrix,0);
        Matrix.rotateM(mModelMatrix,0,180f,1f,0f,0f);
    }

    @Override
    public void onDrawFrame(GL10 gl) {
        GLES20.glClear( GLES20.GL_DEPTH_BUFFER_BIT | GLES20.GL_COLOR_BUFFER_BIT);
        synchronized (this){
            if (updateSurface){
                surfaceTexture.updateTexImage();//获取新数据
                surfaceTexture.getTransformMatrix(mSTMatrix);//让新的纹理和纹理坐标系能够正确的对应,mSTMatrix的定义是和projectionMatrix完全一样的。
                updateSurface = false;
            }
        }
        GLES20.glUseProgram(programId);
        GLES20.glUniformMatrix4fv(uMatrixLocation,1,false,projectionMatrix,0);
        GLES20.glUniformMatrix4fv(uSTMMatrixHandle, 1, false, mSTMatrix, 0);
        GLES20.glUniformMatrix4fv(mHViewMatrix,1,false,mViewMatrix,0);
        GLES20.glUniformMatrix4fv(mHModelMatrix,1,false,mModelMatrix,0);
        GLES20.glUniformMatrix4fv(mHRotateMatrix,1,false,mRotateMatrix,0);

        GLES20.glEnableVertexAttribArray(aPositionLocation);
        GLES20.glVertexAttribPointer(aPositionLocation, 3, GLES20.GL_FLOAT, false,
                0, posBuffer);
        GLES20.glEnableVertexAttribArray(aTextureCoordLocation);
        GLES20.glVertexAttribPointer(aTextureCoordLocation,2,GLES20.GL_FLOAT,false,0,cooBuffer);
        
        GLES20.glActiveTexture(GLES20.GL_TEXTURE0);
        GLES20.glBindTexture(GLES11Ext.GL_TEXTURE_EXTERNAL_OES,textureId);

        GLES20.glUniform1i(uTextureSamplerLocation,0);
        GLES20.glViewport(0,0,screenWidth,screenHeight);
        //GLES20.glDrawArrays(GLES20.GL_TRIANGLE_STRIP, 0, 4);
        GLES20.glDrawArrays(GLES20.GL_TRIANGLES, 0, vCount);//added by wangshuo
    }

    @Override
    synchronized public void onFrameAvailable(SurfaceTexture surface) {
        updateSurface = true;
    }

    @Override
    public void onVideoSizeChanged(MediaPlayer mp, int width, int height) {
        Log.d(TAG, "onVideoSizeChanged: "+width+" "+height);
        //updateProjection(width,height);
    }

    public MediaPlayer getMediaPlayer() {
        return mediaPlayer;
    }

    public void setMatrix(float[] matrix){
        System.arraycopy(matrix,0,mRotateMatrix,0,16);
    }

    private void calculateAttribute(){
        ArrayList<Float> alVertix = new ArrayList<>();
        ArrayList<Float> textureVertix = new ArrayList<>();
        for (double vAngle = 0; vAngle < Math.PI; vAngle = vAngle + angleSpan){

            for (double hAngle = 0; hAngle < 2*Math.PI; hAngle = hAngle + angleSpan){
                float x0 = (float) (radius* Math.sin(vAngle) * Math.cos(hAngle));
                float y0 = (float) (radius* Math.sin(vAngle) * Math.sin(hAngle));
                float z0 = (float) (radius * Math.cos((vAngle)));

                float x1 = (float) (radius* Math.sin(vAngle) * Math.cos(hAngle + angleSpan));
                float y1 = (float) (radius* Math.sin(vAngle) * Math.sin(hAngle + angleSpan));
                float z1 = (float) (radius * Math.cos(vAngle));

                float x2 = (float) (radius* Math.sin(vAngle + angleSpan) * Math.cos(hAngle + angleSpan));
                float y2 = (float) (radius* Math.sin(vAngle + angleSpan) * Math.sin(hAngle + angleSpan));
                float z2 = (float) (radius * Math.cos(vAngle + angleSpan));

                float x3 = (float) (radius* Math.sin(vAngle + angleSpan) * Math.cos(hAngle));
                float y3 = (float) (radius* Math.sin(vAngle + angleSpan) * Math.sin(hAngle));
                float z3 = (float) (radius * Math.cos(vAngle + angleSpan));

                alVertix.add(x1);
                alVertix.add(y1);
                alVertix.add(z1);
                alVertix.add(x0);
                alVertix.add(y0);
                alVertix.add(z0);
                alVertix.add(x3);
                alVertix.add(y3);
                alVertix.add(z3);

                float s0 = (float) (hAngle / Math.PI/2);
                float s1 = (float) ((hAngle + angleSpan)/Math.PI/2);
                float t0 = (float) (vAngle / Math.PI);
                float t1 = (float) ((vAngle + angleSpan) / Math.PI);

                textureVertix.add(s1);// x1 y1对应纹理坐标
                textureVertix.add(t0);
                textureVertix.add(s0);// x0 y0对应纹理坐标
                textureVertix.add(t0);
                textureVertix.add(s0);// x3 y3对应纹理坐标
                textureVertix.add(t1);

                alVertix.add(x1);
                alVertix.add(y1);
                alVertix.add(z1);
                alVertix.add(x3);
                alVertix.add(y3);
                alVertix.add(z3);
                alVertix.add(x2);
                alVertix.add(y2);
                alVertix.add(z2);

                textureVertix.add(s1);// x1 y1对应纹理坐标
                textureVertix.add(t0);
                textureVertix.add(s0);// x3 y3对应纹理坐标
                textureVertix.add(t1);
                textureVertix.add(s1);// x2 y3对应纹理坐标
                textureVertix.add(t1);
            }
        }
        vCount = alVertix.size() / 3;
        posBuffer = convertToFloatBuffer(alVertix);
        cooBuffer=convertToFloatBuffer(textureVertix);
    }

    private FloatBuffer convertToFloatBuffer(ArrayList<Float> data){
        float[] d=new float[data.size()];
        for (int i=0;i<d.length;i++){
            d[i]=data.get(i);
        }

        ByteBuffer buffer=ByteBuffer.allocateDirect(data.size()*4);
        buffer.order(ByteOrder.nativeOrder());
        FloatBuffer ret=buffer.asFloatBuffer();
        ret.put(d);
        ret.position(0);
        return ret;
    }
}