基于OpenGLES的Android相机预览

时间:2022-06-05
本文章向大家介绍基于OpenGLES的Android相机预览,主要内容包括其使用实例、应用技巧、基本知识点总结和需要注意事项,具有一定的参考价值,需要的朋友可以参考一下。

前言

随着AR效果越来越普及,摄像头在Android中的应用越来越重要。通常摄像头的预览方案,通常使用SurfaceView的方案。

SurfaceView使用非常方便,但是我们没法对SurfaceView显示的视频数据进行处理。这样的架构灵活性很差。因此,Android还提供了Texture的方式。摄像头将采集的数据保存成纹理,然后使用Opengles去显示。

Opengles基础

OpenGL- ES 是免授权费的,跨平台和3D图形应用程序接口API。

GLSL

OpenGL着色语言(OpenGL Shading Language)是用来在OpenGL中着色编程的语言,也即开发人员写的短小的自定义程序,他们是在图形卡的GPU (Graphic Processor Unit图形处理单元)上执行的,代替了固定的渲染管线的一部分,使渲染管线中不同层次具有可编程性。

我们通过编写GLSL来决定顶点数据,片段数据以怎样的方式进行组合。

    private final String vertexShaderCode = "uniform mat4 textureTransform;n" +
            "attribute vec2 inputTextureCoordinate;n" +
            "attribute vec4 position;            n" +//NDK坐标点
            "varying   vec2 textureCoordinate; n" +//纹理坐标点变换后输出
            "n" +
            " void main() {n" +
            "     gl_Position = vec4(position.x,-position.y,position.z,position.w);n" +
            "     textureCoordinate = vec2(inputTextureCoordinate.x,inputTextureCoordinate.y);n" +
            " }";

    private final String fragmentShaderCode = "#extension GL_OES_EGL_image_external : requiren" +
            "precision mediump float;n" +
            "uniform samplerExternalOES videoTex;n" +
            "varying vec2 textureCoordinate;n" +
            "n" +
            "void main() {n" +
            "    vec4 tc = texture2D(videoTex, textureCoordinate);n" +
//                "    float color = tc.r * 0.3 + tc.g * 0.59 + tc.b * 0.11;n" +  //所有视图修改成黑白
//                "    gl_FragColor = vec4(color,color,color,1.0);n" +
            "    gl_FragColor = vec4(tc.r,tc.g,tc.b,1.0);n" +
            "}";

上面的代码中,position是输入变量,表示顶点坐标。** gl_Position**是最终的坐标。 例如:

gl_Position = vec4(position.x,-position.y,position.z,position.w);

表示显示图像与源数据上下颠倒。

Program

上面介绍了GLSL(着色器语言)的编写,但我们如何将GLSL写入GPU,让它为我们工作呢?这就需要Program。我们可以将GLSL编写的Shader绑定到特定的Program,然后将Program链接到OpenGL中。

    private int loadShader(int type, String shaderCode) {
        int shader = GLES20.glCreateShader(type);
        // 添加上面编写的着色器代码并编译它
        GLES20.glShaderSource(shader, shaderCode);
        GLES20.glCompileShader(shader);
        return shader;
    }

    private void creatProgram() {
        int vertexShader = loadShader(GLES20.GL_VERTEX_SHADER, vertexShaderCode);
        int fragmentShader = loadShader(GLES20.GL_FRAGMENT_SHADER, fragmentShaderCode);
        // 创建空的OpenGL ES程序
        mProgram = GLES20.glCreateProgram();

        // 添加顶点着色器到程序中
        GLES20.glAttachShader(mProgram, vertexShader);

        // 添加片段着色器到程序中
        GLES20.glAttachShader(mProgram, fragmentShader);

        // 创建OpenGL ES程序可执行文件
        GLES20.glLinkProgram(mProgram);

        // 释放shader资源
        GLES20.glDeleteShader(vertexShader);
        GLES20.glDeleteShader(fragmentShader);
    }

GLSurfaceView.Renderer

GLSurfaceView.Renderer是Android SDK提供的一个接口。需要实现三个方法

  • onSurfaceCreated是画面创建时调用,用于创建Program,初始化纹理等一些初始化工作
  • onSurfaceChanged是画面尺寸变化时调用,通常用于设置尺寸,设置视点
  • onDrawFrame在GPU准备绘制时调用,用于具体的绘制过程

具体过程

创建Render

    public static Camera camera;
    GLSurfaceView mCameraGlsurfaceView;
    public CameraRender mRenderer;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.gl_preview_fragment_layout);

        mCameraGlsurfaceView = findViewById(R.id.glsv_effect_preview);
        mCameraGlsurfaceView.setEGLContextClientVersion(2);//在setRenderer()方法前调用此方法
        mRenderer = new CameraRender(camera , this);
        mCameraGlsurfaceView.setRenderer(mRenderer);
        mCameraGlsurfaceView.setRenderMode(RENDERMODE_WHEN_DIRTY);

        if (camera != null) {
            camera.stopPreview();
            camera.release();
        }
        mRenderer.mBoolean = true;

    }


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

Render

    private int camera_status = 0;
    private final String vertexShaderCode = "uniform mat4 textureTransform;n" +
            "attribute vec2 inputTextureCoordinate;n" +
            "attribute vec4 position;            n" +//NDK坐标点
            "varying   vec2 textureCoordinate; n" +//纹理坐标点变换后输出
            "n" +
            " void main() {n" +
            "     gl_Position = vec4(position.x,-position.y,position.z,position.w);n" +
            "     textureCoordinate = vec2(inputTextureCoordinate.x,inputTextureCoordinate.y);n" +
            " }";

    private final String fragmentShaderCode = "#extension GL_OES_EGL_image_external : requiren" +
            "precision mediump float;n" +
            "uniform samplerExternalOES videoTex;n" +
            "varying vec2 textureCoordinate;n" +
            "n" +
            "void main() {n" +
            "    vec4 tc = texture2D(videoTex, textureCoordinate);n" +
//                "    float color = tc.r * 0.3 + tc.g * 0.59 + tc.b * 0.11;n" +  //所有视图修改成黑白
//                "    gl_FragColor = vec4(color,color,color,1.0);n" +
            "    gl_FragColor = vec4(tc.r,tc.g,tc.b,1.0);n" +
            "}";
    private float[] mPosCoordinate = {-1, -1, -1, 1, 1, -1, 1, 1};
    private float[] mTexCoordinateBackRight = {1, 1, 0, 1, 1, 0, 0, 0};//顺时针转90并沿Y轴翻转  后摄像头正确,前摄像头上下颠倒
    private float[] mTexCoordinateForntRight = {0, 1, 1, 1, 0, 0, 1, 0};//顺时针旋转90  后摄像头上下颠倒了,前摄像头正确
    private SurfaceTexture mSurfaceTexture;
    private Camera mCamera;
    private SurfaceTexture.OnFrameAvailableListener mOnFrameAvailableListener;

    public int mProgram;
    public boolean mBoolean = false;

    public CameraRender( Camera camera , SurfaceTexture.OnFrameAvailableListener listener) {
        mCamera = camera;
        mOnFrameAvailableListener = listener;
        Matrix.setIdentityM(mProjectMatrix, 0);
        Matrix.setIdentityM(mCameraMatrix, 0);
        Matrix.setIdentityM(mMVPMatrix, 0);
    }

onSurfaceCreated

    /**
     * 加载着色器
     * @param type 着色器类型
     * @param shaderCode 着色器源码
     * @return
     */
    private int loadShader(int type, String shaderCode) {
        int shader = GLES20.glCreateShader(type);
        // 添加上面编写的着色器代码并编译它
        GLES20.glShaderSource(shader, shaderCode);
        GLES20.glCompileShader(shader);
        return shader;
    }

    private void creatProgram() {
        int vertexShader = loadShader(GLES20.GL_VERTEX_SHADER, vertexShaderCode);
        int fragmentShader = loadShader(GLES20.GL_FRAGMENT_SHADER, fragmentShaderCode);
        // 创建空的OpenGL ES程序
        mProgram = GLES20.glCreateProgram();

        // 添加顶点着色器到程序中
        GLES20.glAttachShader(mProgram, vertexShader);

        // 添加片段着色器到程序中
        GLES20.glAttachShader(mProgram, fragmentShader);

        // 创建OpenGL ES程序可执行文件
        GLES20.glLinkProgram(mProgram);

        // 释放shader资源
        GLES20.glDeleteShader(vertexShader);
        GLES20.glDeleteShader(fragmentShader);
    }

    @Override
    public void onSurfaceCreated(GL10 gl, EGLConfig config) {
        GLES20.glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
        mSurfaceTexture = new SurfaceTexture(createOESTextureObject());
        creatProgram();
        mCamera = Camera.open(1);
        try {
            mCamera.setPreviewTexture(mSurfaceTexture);
            mCamera.startPreview();
        } catch (IOException e) {
            e.printStackTrace();
        }

    }

在onSurfaceCreated中,我们不仅创建了Program,还初始化了SurfaceTexture和Camera。其中,SurfaceTexture通过createOESTextureObject获取。

onSurfaceChanged

    @Override
    public void onSurfaceChanged(GL10 gl, int width, int height) {
        GLES20.glViewport(0, 0, width, height);
        Matrix.scaleM(mMVPMatrix,0,1,-1,1);
        float ratio = (float) width / height;
        Matrix.orthoM(mProjectMatrix, 0, -1, 1, -ratio, ratio, 1, 7);// 3和7代表远近视点与眼睛的距离,非坐标点
        Matrix.setLookAtM(mCameraMatrix, 0, 0, 0, 3, 0f, 0f, 0f, 0f, 1.0f, 0.0f);// 3代表眼睛的坐标点
        Matrix.multiplyMM(mMVPMatrix, 0, mProjectMatrix, 0, mCameraMatrix, 0);
    }

onDrawFrame

    //添加程序到ES环境中
    private void activeProgram() {
        // 将程序添加到OpenGL ES环境
        GLES20.glUseProgram(mProgram);
        mSurfaceTexture.setOnFrameAvailableListener(mOnFrameAvailableListener);
        // 获取顶点着色器的位置的句柄
        uPosHandle = GLES20.glGetAttribLocation(mProgram, "position");
        aTexHandle = GLES20.glGetAttribLocation(mProgram, "inputTextureCoordinate");

        FloatBuffer mPosBuffer = convertToFloatBuffer(mPosCoordinate);
        FloatBuffer mTexBuffer;
        if(camera_status == 0){
            mTexBuffer = convertToFloatBuffer(mTexCoordinateBackRight);
        }else{
            mTexBuffer = convertToFloatBuffer(mTexCoordinateForntRight);
        }

        GLES20.glVertexAttribPointer(uPosHandle, 2, GLES20.GL_FLOAT, false, 0, mPosBuffer);
        GLES20.glVertexAttribPointer(aTexHandle, 2, GLES20.GL_FLOAT, false, 0, mTexBuffer);

        // 启用顶点位置的句柄
        GLES20.glEnableVertexAttribArray(uPosHandle);
        GLES20.glEnableVertexAttribArray(aTexHandle);
    }


    @Override
    public void onDrawFrame(GL10 gl) {
        if(mBoolean){
            activeProgram();
            mBoolean = false;
        }
        if (mSurfaceTexture != null) {
            GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT | GLES20.GL_DEPTH_BUFFER_BIT);
            mSurfaceTexture.updateTexImage();
            GLES20.glDrawArrays(GLES20.GL_TRIANGLE_STRIP, 0, mPosCoordinate.length / 2);
        }
    }

在onDrawFrame中,我们使用Program,并传入对应的position,然后更新SurfaceTexture,并重绘画面。

经过以上的过程,我们可以在Android中显示摄像头的画面。

如有问题,欢迎指正。