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FFmpeg 开发系列连载：

FFmpeg 开发 (01)：FFmpeg 编译和集成
FFmpeg 开发 (02)：FFmpeg + ANativeWindow 实现视频解码播放
FFmpeg 开发 (03)：FFmpeg + OpenSLES 实现音频解码播放
FFmpeg 开发 (04)：FFmpeg + OpenGLES 实现音频可视化播放

后面 Android FFmpeg 开发系列文章中，咱们曾经利用 FFmpeg 的解码性能和 ANativeWindow 的渲染性能，实现了的视频的解码播放。然而，当你想为播放器做一些视频滤镜时，如加水印、旋转缩放等成果，应用 OpenGL ES 实现起来就极为不便。

OpenGLES 渲染解码帧

通过下面几节的介绍，咱们对音视频的解码过程曾经比拟相熟了。本文要用 OpenGL 实现视频的渲染，这里再回顾下视频的解码流程：

从流程图中能够看出，解码一帧图像后，首先将对图像进行格局转换，转换成 RGBA 格局，应用 OpenGL 或 ANativeWindow 能够间接进行渲染。

当然，应用 OpenGL 进行渲染时，为了晋升性能，能够将格局转换放到 GPU 上来做（即 shader 实现 YUV 到 RGB 的转换），也能够应用 OES 纹理间接接管 YUV 图像数据，这里就不进行开展讲了。

理解视频解码到渲染的流程之后，咱们就能够构建 OpenGL 渲染环境。从之前介绍 EGL 的文章中，咱们晓得在应用 OpenGL API 之前，必须要先利用 EGL 创立好 OpenGL 的渲染上下文环境。至于 EGL 怎么应用，能够参考文章 OpenGLES 与 EGL 的关系。

因为本文是面向初学者疾速上手 FFmpeg 开发，咱们间接利用 Android GLSurfaceView 类创立 OpenGL 渲染环境，GLSurfaceView 类曾经封装了 EGL 创立渲染上下文的操作，并启动了一个独立的渲染线程，完全符合咱们渲染视频解码帧的需要。

实际上，GLSurfaceView 类在生产开发中能够满足绝大多数的屏幕渲染场景，个别要实现多线程渲染的时候才须要咱们独自操作 EGL 的接口。

那么，你必定会有疑难：GLSurfaceView 是 Java 的类，难道要将 Native 层解码后的视频图像传到 Java 层再进行渲染吗？大可不必，咱们只须要将 Java 层的调用栈通过 JNI 延长到 Native 层即可。

GLSurfaceView 类 Renderer 接口对应渲染的三个要害函数，咱们通过 JNI 延长到 Native 层：

    @Override
    public void onSurfaceCreated(GL10 gl10, EGLConfig eglConfig) {FFMediaPlayer.native_OnSurfaceCreated();
    }

    @Override
    public void onSurfaceChanged(GL10 gl10, int w, int h) {FFMediaPlayer.native_OnSurfaceChanged(w, h);
    }

    @Override
    public void onDrawFrame(GL10 gl10) {FFMediaPlayer.native_OnDrawFrame();
    }

    //for video openGL render
    public static native void native_OnSurfaceCreated();
    public static native void native_OnSurfaceChanged(int width, int height);
    public static native void native_OnDrawFrame();

而后，咱们在 Native 层创立一个 OpenGLRender 类来用来治理 OpenGL 的渲染。

// 接口
class VideoRender {
public:
    virtual ~VideoRender(){}
    virtual void Init(int videoWidth, int videoHeight, int *dstSize) = 0;
    virtual void RenderVideoFrame(NativeImage *pImage) = 0;
    virtual void UnInit() = 0;};

//OpenGLRender 类定义
class OpenGLRender: public VideoRender{
public:
    virtual void Init(int videoWidth, int videoHeight, int *dstSize);
    virtual void RenderVideoFrame(NativeImage *pImage);
    virtual void UnInit();

    // 对应 Java 层 GLSurfaceView.Renderer 的三个接口
    void OnSurfaceCreated();
    void OnSurfaceChanged(int w, int h);
    void OnDrawFrame();
    
    // 动态实例治理
    static OpenGLRender *GetInstance();
    static void ReleaseInstance();
    
    // 设置变换矩阵，管制图像的旋转缩放
    void UpdateMVPMatrix(int angleX, int angleY, float scaleX, float scaleY);

private:
    OpenGLRender();
    virtual ~OpenGLRender();

    static std::mutex m_Mutex;
    static OpenGLRender* s_Instance;
    GLuint m_ProgramObj = GL_NONE;
    GLuint m_TextureId;
    GLuint m_VaoId;
    GLuint m_VboIds[3];
    NativeImage m_RenderImage;
    glm::mat4 m_MVPMatrix;// 变换矩阵
};

OpenGLRender 类的残缺实现。

#include "OpenGLRender.h"
#include <GLUtils.h>
#include <gtc/matrix_transform.hpp>

OpenGLRender* OpenGLRender::s_Instance = nullptr;
std::mutex OpenGLRender::m_Mutex;

static char vShaderStr[] =
        "#version 300 es\n"
        "layout(location = 0) in vec4 a_position;\n"
        "layout(location = 1) in vec2 a_texCoord;\n"
        "uniform mat4 u_MVPMatrix;\n"
        "out vec2 v_texCoord;\n"
        "void main()\n"
        "{\n"
        "gl_Position = u_MVPMatrix * a_position;\n"
        "v_texCoord = a_texCoord;\n"
        "}";

static char fShaderStr[] =
        "#version 300 es\n"
        "precision highp float;\n"
        "in vec2 v_texCoord;\n"
        "layout(location = 0) out vec4 outColor;\n"
        "uniform sampler2D s_TextureMap;// 采样器 \n"
        "void main()\n"
        "{\n"
        "outColor = texture(s_TextureMap, v_texCoord);\n"
        "}";

GLfloat verticesCoords[] = {
        -1.0f,  1.0f, 0.0f,  // Position 0
        -1.0f, -1.0f, 0.0f,  // Position 1
        1.0f,  -1.0f, 0.0f,  // Position 2
        1.0f,   1.0f, 0.0f,  // Position 3
};

GLfloat textureCoords[] = {
        0.0f,  0.0f,        // TexCoord 0
        0.0f,  1.0f,        // TexCoord 1
        1.0f,  1.0f,        // TexCoord 2
        1.0f,  0.0f         // TexCoord 3
};

GLushort indices[] = { 0, 1, 2, 0, 2, 3};

OpenGLRender::OpenGLRender() {}

OpenGLRender::~OpenGLRender() {
    // 开释缓存图像
    NativeImageUtil::FreeNativeImage(&m_RenderImage);

}

// 初始化视频图像的宽和高
void OpenGLRender::Init(int videoWidth, int videoHeight, int *dstSize) {LOGCATE("OpenGLRender::InitRender video[w, h]=[%d, %d]", videoWidth, videoHeight);
    std::unique_lock<std::mutex> lock(m_Mutex);
    m_RenderImage.format = IMAGE_FORMAT_RGBA;
    m_RenderImage.width = videoWidth;
    m_RenderImage.height = videoHeight;
    dstSize[0] = videoWidth;
    dstSize[1] = videoHeight;
    m_FrameIndex = 0;

}

// 接管解码后的视频帧
void OpenGLRender::RenderVideoFrame(NativeImage *pImage) {LOGCATE("OpenGLRender::RenderVideoFrame pImage=%p", pImage);
    if(pImage == nullptr || pImage->ppPlane[0] == nullptr)
        return;
    // 加互斥锁，解码线程和渲染线程是 2 个不同的线程，防止数据拜访抵触
    std::unique_lock<std::mutex> lock(m_Mutex);
    if(m_RenderImage.ppPlane[0] == nullptr)
    {NativeImageUtil::AllocNativeImage(&m_RenderImage);
    }

    NativeImageUtil::CopyNativeImage(pImage, &m_RenderImage);
}

void OpenGLRender::UnInit() {}

// 设置变换矩阵，管制图像的旋转缩放
void OpenGLRender::UpdateMVPMatrix(int angleX, int angleY, float scaleX, float scaleY)
{
    angleX = angleX % 360;
    angleY = angleY % 360;

    // 转化为弧度角
    float radiansX = static_cast<float>(MATH_PI / 180.0f * angleX);
    float radiansY = static_cast<float>(MATH_PI / 180.0f * angleY);
    // Projection matrix
    glm::mat4 Projection = glm::ortho(-1.0f, 1.0f, -1.0f, 1.0f, 0.1f, 100.0f);
    //glm::mat4 Projection = glm::frustum(-ratio, ratio, -1.0f, 1.0f, 4.0f, 100.0f);
    //glm::mat4 Projection = glm::perspective(45.0f,ratio, 0.1f,100.f);

    // View matrix
    glm::mat4 View = glm::lookAt(glm::vec3(0, 0, 4), // Camera is at (0,0,1), in World Space
            glm::vec3(0, 0, 0), // and looks at the origin
            glm::vec3(0, 1, 0)  // Head is up (set to 0,-1,0 to look upside-down)
    );

    // Model matrix
    glm::mat4 Model = glm::mat4(1.0f);
    Model = glm::scale(Model, glm::vec3(scaleX, scaleY, 1.0f));
    Model = glm::rotate(Model, radiansX, glm::vec3(1.0f, 0.0f, 0.0f));
    Model = glm::rotate(Model, radiansY, glm::vec3(0.0f, 1.0f, 0.0f));
    Model = glm::translate(Model, glm::vec3(0.0f, 0.0f, 0.0f));

    m_MVPMatrix = Projection * View * Model;

}

void OpenGLRender::OnSurfaceCreated() {LOGCATE("OpenGLRender::OnSurfaceCreated");

    m_ProgramObj = GLUtils::CreateProgram(vShaderStr, fShaderStr);
    if (!m_ProgramObj)
    {LOGCATE("OpenGLRender::OnSurfaceCreated create program fail");
        return;
    }

    glGenTextures(1, &m_TextureId);
    glBindTexture(GL_TEXTURE_2D, m_TextureId);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glBindTexture(GL_TEXTURE_2D, GL_NONE);

    // Generate VBO Ids and load the VBOs with data
    glGenBuffers(3, m_VboIds);
    glBindBuffer(GL_ARRAY_BUFFER, m_VboIds[0]);
    glBufferData(GL_ARRAY_BUFFER, sizeof(verticesCoords), verticesCoords, GL_STATIC_DRAW);

    glBindBuffer(GL_ARRAY_BUFFER, m_VboIds[1]);
    glBufferData(GL_ARRAY_BUFFER, sizeof(textureCoords), textureCoords, GL_STATIC_DRAW);

    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, m_VboIds[2]);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);

    // Generate VAO Id
    glGenVertexArrays(1, &m_VaoId);
    glBindVertexArray(m_VaoId);

    glBindBuffer(GL_ARRAY_BUFFER, m_VboIds[0]);
    glEnableVertexAttribArray(0);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), (const void *)0);
    glBindBuffer(GL_ARRAY_BUFFER, GL_NONE);

    glBindBuffer(GL_ARRAY_BUFFER, m_VboIds[1]);
    glEnableVertexAttribArray(1);
    glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 2 * sizeof(GLfloat), (const void *)0);
    glBindBuffer(GL_ARRAY_BUFFER, GL_NONE);

    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, m_VboIds[2]);

    glBindVertexArray(GL_NONE);

    UpdateMVPMatrix(0, 0, 1.0f, 1.0f);
}

void OpenGLRender::OnSurfaceChanged(int w, int h) {LOGCATE("OpenGLRender::OnSurfaceChanged [w, h]=[%d, %d]", w, h);
    m_ScreenSize.x = w;
    m_ScreenSize.y = h;
    glViewport(0, 0, w, h);
    glClearColor(1.0f, 1.0f, 1.0f, 1.0f);
}

void OpenGLRender::OnDrawFrame() {glClear(GL_COLOR_BUFFER_BIT);
    if(m_ProgramObj == GL_NONE || m_TextureId == GL_NONE || m_RenderImage.ppPlane[0] == nullptr) return;
    LOGCATE("OpenGLRender::OnDrawFrame [w, h]=[%d, %d]", m_RenderImage.width, m_RenderImage.height);
    m_FrameIndex++;

    //upload RGBA image data
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, m_TextureId);

    // 加互斥锁，解码线程和渲染线程是 2 个不同的线程，防止数据拜访抵触
    std::unique_lock<std::mutex> lock(m_Mutex);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, m_RenderImage.width, m_RenderImage.height, 0, GL_RGBA, GL_UNSIGNED_BYTE, m_RenderImage.ppPlane[0]);
    lock.unlock();

    glBindTexture(GL_TEXTURE_2D, GL_NONE);

    // Use the program object
    glUseProgram (m_ProgramObj);

    glBindVertexArray(m_VaoId);

    GLUtils::setMat4(m_ProgramObj, "u_MVPMatrix", m_MVPMatrix);

    // Bind the RGBA map
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, m_TextureId);
    GLUtils::setFloat(m_ProgramObj, "s_TextureMap", 0);

    glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_SHORT, (const void *)0);

}

// 单例模式，全局只有一个 OpenGLRender
OpenGLRender *OpenGLRender::GetInstance() {if(s_Instance == nullptr)
    {std::lock_guard<std::mutex> lock(m_Mutex);
        if(s_Instance == nullptr)
        {s_Instance = new OpenGLRender();
        }

    }
    return s_Instance;
}

// 开释动态实例
void OpenGLRender::ReleaseInstance() {if(s_Instance != nullptr)
    {std::lock_guard<std::mutex> lock(m_Mutex);
        if(s_Instance != nullptr)
        {
            delete s_Instance;
            s_Instance = nullptr;
        }

    }
}

OpenGLRender 在 JNI 层的调用。

JNIEXPORT void JNICALL
Java_com_byteflow_learnffmpeg_media_FFMediaPlayer_native_1OnSurfaceCreated(JNIEnv *env,
                                                                           jclass clazz) {OpenGLRender::GetInstance()->OnSurfaceCreated();}

JNIEXPORT void JNICALL
Java_com_byteflow_learnffmpeg_media_FFMediaPlayer_native_1OnSurfaceChanged(JNIEnv *env,
                                                                           jclass clazz, jint width,
                                                                           jint height) {OpenGLRender::GetInstance()->OnSurfaceChanged(width, height);
}

JNIEXPORT void JNICALL
Java_com_byteflow_learnffmpeg_media_FFMediaPlayer_native_1OnDrawFrame(JNIEnv *env, jclass clazz) {OpenGLRender::GetInstance()->OnDrawFrame();}

增加简略的视频滤镜

这里又回到了 OpenGL ES 开发畛域，对这一块感兴趣的同学能够参考这篇 Android OpenGL ES 从入门到精通系统性学习教程。

利用 OpenGL 实现好视频的渲染之后，能够很不便地利用 shader 增加你想要的视频滤镜，这里咱们间接能够参考相机滤镜的实现。

黑白滤镜

咱们将输入视频帧的一半渲染成经典黑白格调的图像，实现的 shader 如下：

// 黑白滤镜
#version 300 es
precision highp float;
in vec2 v_texCoord;
layout(location = 0) out vec4 outColor;
uniform sampler2D s_TextureMap;// 采样器
void main()
{outColor = texture(s_TextureMap, v_texCoord);
    if(v_texCoord.x > 0.5) // 将输入视频帧的一半渲染成经典黑白格调的图像
        outColor = vec4(vec3(outColor.r*0.299 + outColor.g*0.587 + outColor.b*0.114), outColor.a);
}

黑白滤镜的出现成果:

动静网格

动静网格滤镜是将视频图像分成规定的网格，动静批改网格的边框宽度，实现的 shader 如下：

//dynimic mesh 动静网格
#version 300 es
precision highp float;
in vec2 v_texCoord;
layout(location = 0) out vec4 outColor;
uniform sampler2D s_TextureMap;// 采样器
uniform float u_Offset;
uniform vec2 u_TexSize;
void main()
{
    vec2 imgTexCoord = v_texCoord * u_TexSize;
    float sideLength = u_TexSize.y / 6.0;
    float maxOffset = 0.15 * sideLength;
    float x = mod(imgTexCoord.x, floor(sideLength));
    float y = mod(imgTexCoord.y, floor(sideLength));

    float offset = u_Offset * maxOffset;

    if(offset <= x
    && x <= sideLength - offset
    && offset <= y
    && y <= sideLength - offset)
    {outColor = texture(s_TextureMap, v_texCoord);
    }
    else
    {outColor = vec4(1.0, 1.0, 1.0, 1.0);
    }
}

动静网格滤镜的渲染过程：

glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, m_TextureId);

std::unique_lock<std::mutex> lock(m_Mutex);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, m_RenderImage.width, m_RenderImage.height, 0, GL_RGBA, GL_UNSIGNED_BYTE, m_RenderImage.ppPlane[0]);
lock.unlock();

glBindTexture(GL_TEXTURE_2D, GL_NONE);

// 指定着色器程序
glUseProgram (m_ProgramObj);

// 绑定 VAO
glBindVertexArray(m_VaoId);

// 传入变换矩阵
GLUtils::setMat4(m_ProgramObj, "u_MVPMatrix", m_MVPMatrix);

// 绑定纹理
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, m_TextureId);
GLUtils::setFloat(m_ProgramObj, "s_TextureMap", 0);

// 设置偏移量
float offset = (sin(m_FrameIndex * MATH_PI / 25) + 1.0f) / 2.0f;
GLUtils::setFloat(m_ProgramObj, "u_Offset", offset);

// 设置图像尺寸
GLUtils::setVec2(m_ProgramObj, "u_TexSize", vec2(m_RenderImage.width, m_RenderImage.height));

glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_SHORT, (const void *)0);

动静网格滤镜的出现成果:

缩放和旋转

咱们在 GLSurfaceView 监听用户的滑动和缩放手势，管制 OpenGLRender 的变换矩阵，从而实现视频图像的旋转和缩放。

分割与交换

有疑难或技术交换能够增加我的微信：Byte-Flow