上篇博客基于live555的rtsp播放器：使用SDL2\D3D9渲染yuv420p中指出在mac上使用SDL2会有问题，因此在mac上可以使用QOpenGLWidget渲染yuv420p。

一.GLSL Versions

You can use the #version command as the first line of your shader to specify GLSL version:

#version 120

void main() {
    gl_FragColor = vec4(1.0);
}

GLSL versions are released alongside GL versions. See the following charts to decide which version you would like to target.

OpenGL Version	GLSL Version
2.0	110
2.1	120
3.0	130
3.1	140
3.2	150
3.3	330
4.0	400
4.1	410
4.2	420
4.3	430

GLSL ES Versions (Android, iOS, WebGL)

OpenGL ES has its own Shading Language, and the versioning starts fresh. It is based on OpenGL Shading Language version 1.10.

OpenGL ES Version	GLSL ES Version
2.0	100
3.0	300

So, for example, if a feature is available in GLSL 120, it probably won't be available in GLSL ES 100 unless the ES compiler specifically allows it.

Differences at a Glance

Differences between (desktop) GLSL versions.

Version 100

Vertex shader:

uniform mat4 projTrans;

attribute vec2 Position;
attribute vec2 TexCoord;

varying vec2 vTexCoord;

void main() {
	vTexCoord = TexCoord;
	gl_Position = u_projView * vec4(Position, 0.0, 1.0);
}

Fragment shader:

uniform sampler2D tex0;

varying vec2 vTexCoord;

void main() {
    vec4 color = texture2D(tex0, vTexCoord);
    gl_FragColor = color;
}

Version 330

As of GLSL 130+, in and out are used instead of attribute and varying. GLSL 330+ includes other features like layout qualifiers and changes texture2D to texture.

Vertex shader:

#version 330

uniform mat4 projTrans;

layout(location = 0) in vec2 Position;
layout(location = 1) in vec2 TexCoord;

out vec2 vTexCoord;

void main() {
	vTexCoord = TexCoord;
	gl_Position = u_projView * vec4(Position, 0, 1);
}

Fragment shader:

#version 330
uniform sampler2D tex0;

in vec2 vTexCoord;

//use your own output instead of gl_FragColor 
out vec4 fragColor;

void main() {
    //'texture' instead of 'texture2D'
    fragColor = texture(tex0, vTexCoord);
}

Other Significant Changes

GLSL 120 Additions

You can initialize arrays within a shader, like so:

float a[5] = float[5](3.4, 4.2, 5.0, 5.2, 1.1);
float b[5] = float[](3.4, 4.2, 5.0, 5.2, 1.1);

However, the above is not supported on Mac OSX Snow Leopard, even with GLSL 120. (1)

You can initialize uniforms in a shader, and the value will be set at link time:

uniform float val = 1.0;

You can use built-ins like sin() when setting a const value
Integers are implicitly converted to floats when necessary, for example:

float f = 1.0; <-- valid
float g = 1; <-- only supported in GLSL 120
vec2 v = vec2(1, 2.0); <-- only supported in GLSL 120

You can use f to define a float: float f = 2.5f;

GLSL 130 Additions

int and uint support (and bitwise operations with them)
switch statement support
New built-ins: trunc(), round(), roundEven(), isnan(), isinf(), modf()
Fragment output can be user-defined
Input and output is declared with in and out syntax instead of attribute and varying

GLSL 150 Additions

texture() should now be used instead of texture2D()

GLSL 330 Additions

Layout qualifiers can declare the location of vertex shader inputs and fragment shader outputs, eg:

layout(location = 2) in vec3 values[4];

Formally this was only possible with ARB_explicit_attrib_location extension

参考链接：https://github.com/mattdesl/lwjgl-basics/wiki/GLSL-Versions

二.OpenGL渲染视频

#include "QHOpenGLPlayer.h"

QHOpenGLThread::QHOpenGLThread(QObject *parent)
    :QThread (parent)
{
    m_fileName="Wildlife.yuv";
}

QHOpenGLThread::~QHOpenGLThread()
{

}

void QHOpenGLThread::run()
{
    FILE *pFile = fopen(m_fileName.toStdString().c_str(), "rb");
    if (pFile == nullptr)
    {
        qDebug()<<"fopen failed";
    }
    // Y+U+V
    int bufferSize = VIDEO_WIDTH*VIDEO_HEIGHT+VIDEO_WIDTH*VIDEO_HEIGHT/4+VIDEO_WIDTH*VIDEO_HEIGHT/4;
    uint8_t *buffer = (uint8_t *) malloc(bufferSize);
    while (true)
    {
        if (fread(buffer, 1, bufferSize, pFile) != bufferSize)
        {
            qDebug()<<"end of file";
            break;
        }

        emit signalNewFrame(buffer,VIDEO_WIDTH,VIDEO_HEIGHT);
        msleep(1000/29.97);
    }
}


QHOpenGLPlayer::QHOpenGLPlayer(QWidget *parent)
    : QOpenGLWidget(parent)
    , m_buffer(nullptr)
    , m_width(0)
    , m_height(0)
{
    m_thread=new QHOpenGLThread();
    connect(m_thread,&QHOpenGLThread::signalNewFrame,this,&QHOpenGLPlayer::slotNewFrame,Qt::QueuedConnection);
    m_thread->start();
}

QHOpenGLPlayer::~QHOpenGLPlayer()
{
}

void QHOpenGLPlayer::initializeGL()
{
    initializeOpenGLFunctions();
    glClearColor(0.0, 0.0, 0.0, 1.0);
    const char *vSrc =
            "#version 330                             \n"
            "layout (location = 0) in vec4 verPosIn;  \n"
            "layout (location = 1) in vec2 texPosIn;  \n"
            "out vec2 texPosOut;                      \n"
            "void main(void)                          \n"
            "{                                        \n"
            "    gl_Position = verPosIn;              \n"
            "    texPosOut = texPosIn;                \n"
            "}";

    const char *fSrc =
            "#version 330                                      \n"
            "out vec4 fragColor;                               \n"
            "in vec2 texPosOut;                                \n"
            "uniform sampler2D texY;                           \n"
            "uniform sampler2D texU;                           \n"
            "uniform sampler2D texV;                           \n"
            "void main(void)                                   \n"
            "{                                                 \n"
            "    vec3 yuv;                                     \n"
            "    vec3 rgb;                                     \n"
            "    yuv.x = texture(texY, texPosOut).r;           \n"
            "    yuv.y = texture(texU, texPosOut).r-0.5;       \n"
            "    yuv.z = texture(texV, texPosOut).r-0.5;       \n"
            "    rgb = mat3(1.0, 1.0, 1.0,                     \n"
            "               0.0, -0.3455, 1.779,               \n"
            "               1.4075, -0.7169, 0.0) * yuv;       \n"
            "    fragColor = vec4(rgb, 1.0);                   \n"
            "}";

    m_shaderProgram.addCacheableShaderFromSourceCode(QOpenGLShader::Vertex,vSrc);
    m_shaderProgram.addCacheableShaderFromSourceCode(QOpenGLShader::Fragment,fSrc);
    m_shaderProgram.link();

    m_vbo.create();

    GLuint ids[3];
    glGenTextures(3,ids);
    m_idY = ids[0];
    m_idU = ids[1];
    m_idV = ids[2];
}

void QHOpenGLPlayer::resizeGL(int width, int height)
{
    glViewport(0, 0, width, height);
}

void QHOpenGLPlayer::paintGL()
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glDisable(GL_DEPTH_TEST);

    float x=0.0,y=0.0;
    float wRatio = (float)width()/m_width;
    float hRatio = (float)height()/m_height;
    float minRatio = qMin(wRatio, hRatio);
    x = m_width*minRatio/width();
    y = m_height*minRatio/height();

    GLfloat vertices[]{
        -1.0f*x, -1.0f*y,
         1.0f*x, -1.0f*y,
        -1.0f*x, 1.0f*y,
         1.0f*x, 1.0f*y,

        0.0f, 1.0f,
        1.0f, 1.0f,
        0.0f, 0.0f,
        1.0f, 0.0f
    };

    m_shaderProgram.bind();
    m_vbo.bind();
    m_vbo.allocate(vertices,sizeof(vertices));
    m_shaderProgram.enableAttributeArray(0);
    m_shaderProgram.enableAttributeArray(1);
    m_shaderProgram.setAttributeBuffer(0,GL_FLOAT,0,2,2*sizeof(GLfloat));
    m_shaderProgram.setAttributeBuffer(1,GL_FLOAT,2*4*sizeof(GLfloat),2,2*sizeof(GLfloat));

    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D,m_idY);
    glTexImage2D(GL_TEXTURE_2D,0,GL_RED,m_width,m_height,0,GL_RED,GL_UNSIGNED_BYTE,m_buffer);
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

    glActiveTexture(GL_TEXTURE0+1);
    glBindTexture(GL_TEXTURE_2D,m_idU);
    glTexImage2D(GL_TEXTURE_2D,0,GL_RED,m_width/2,m_height/2,0,GL_RED,GL_UNSIGNED_BYTE,m_buffer+m_width*m_height);
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

    glActiveTexture(GL_TEXTURE0+2);
    glBindTexture(GL_TEXTURE_2D,m_idV);
    glTexImage2D(GL_TEXTURE_2D,0,GL_RED,m_width/2,m_height/2,0,GL_RED,GL_UNSIGNED_BYTE,m_buffer+m_width*m_height*5/4);
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);


    m_shaderProgram.setUniformValue("texY",0);
    m_shaderProgram.setUniformValue("texU",1);
    m_shaderProgram.setUniformValue("texV",2);
    glDrawArrays(GL_TRIANGLE_STRIP,0,4);
    m_shaderProgram.disableAttributeArray(0);
    m_shaderProgram.disableAttributeArray(1);
    m_vbo.release();
    m_shaderProgram.release();
}

void QHOpenGLPlayer::slotNewFrame(uchar *buffer,int width,int height)
{
    m_buffer = buffer;
    m_width = width;
    m_height = height;

    update();
}

代码参考了博客：https://blog.csdn.net/leixiaohua1020/article/details/40379845

关于着色器部分略作修改，使用的GLSL版本是330，因为该版本之前的写法在windows上虽然可以正常显示，但是在linux和mac上却没显示任何内容。
从代码可以看出，如果视频帧的宽和高分别为w和h，那么一帧YUV420P像素数据一共占用w*h*3/2 Byte的数据。其中前w*h Byte存储Y，接着的w*h*1/4 Byte存储U，最后w*h*1/4 Byte存储V。
至于着色器中in、out、location等关键字的意义以及流程中各个函数的用法，可以参考我之前翻译的几篇文章。

Qt OpenGL:学习现代3D图形编程之一，画一个三角形
 Qt OpenGL:学习现代3D图形编程之二，玩转色彩
 Qt OpenGL:学习现代3D图形编程之三，移动三角形

三.效果

源码链接：https://download.csdn.net/download/caoshangpa/14105525

原创不易，转载请标明出处：https://blog.csdn.net/caoshangpa/article/details/112448207

基于live555的rtsp播放器：使用QOpenGLWidget渲染yuv420p

一.GLSL Versions

二.OpenGL渲染视频

三.效果

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