最近因为工作所需，需要采用GPU绘制视频，那么就需要学习OpenGL了； 在学习纹理时，接触的第一个例子是《霍亚飞-Qt Creator快速入门_第三版》中第12章-12.4-使用纹理绘图，然而按照书中所示代码运行时，运行时只显示一个黑窗口，并没有将纹理给贴出来；倒腾了一番功夫，终于跑起来了，先记录一下，后续，，，，，，

QOpenGLShader::compile(Fragment): ERROR: 3:6: ‘texture’ : no matching overloaded function found (using implicit conversion)
ERROR: 3:6: ‘texture’ : function is not known
ERROR: 3:5: ‘assign’ : cannot convert from ‘const highp float’ to ‘FragUserData 4-component vector of highp float’
*** Problematic Fragment shader source code ***
#version 130 core
#define lowp
#define mediump
#define highp
#line 1
uniform sampler2D tex;
in vec4 texCoord;
out vec4 fColor;
void main() {
fColor = texture(tex, texCoord);
}

1. 定位到的报错的代码：

2. 错误的运行结果：

以上是截取的部分关键代码，从错误提示以及运行测试，可以明确的定位错误就是由于红框中的texture()函数引起的，这个是OpenGL内置的函数；但是为什么出错，这心里是一点思路都没有，毕竟这个OpenGL对我来说还是相当陌生的;百度了一圈，也没有相关解答，试了各种方法，均是不行；
最后参考可Qt自带的OpenGL相关的demo，发现需要将texture()函数中的第二个参数加.st后缀，
此时运行就ok了！

3. 改变后的代码：

4. 运行的正确结果：

5. 源码：

#include <QOpenGLWidget>
#include <QOpenGLFunctions>
#include <QOpenGLShaderProgram>
#include <QOpenGLBuffer>
#include <QMatrix4x4>
#include <QOpenGLTexture>
#include <QDebug>

/*纹理贴图*/
class OpenGLWidget5 : public QOpenGLWidget, QOpenGLFunctions
{
    Q_OBJECT
public:
    OpenGLWidget5(QWidget* parent = nullptr);
protected:
    void initializeGL() override;
    void paintGL() override;
private:
    QOpenGLShaderProgram* m_program = nullptr;
    QOpenGLBuffer* m_buffer = nullptr;
    QOpenGLTexture* m_textures[2] ;
};

#include "OpenGLWidget5.h"

OpenGLWidget5::OpenGLWidget5(QWidget *parent)
    :QOpenGLWidget(parent)
{
    m_buffer = new QOpenGLBuffer;
}

void OpenGLWidget5::initializeGL()
{
    initializeOpenGLFunctions();
    for(int i = 0; i < 2; i++) {
       m_textures[i] = new QOpenGLTexture(QImage(QString(":/image/side%1.png").arg(i+1)).mirrored());
    }
    const char* vsrc = "in vec4 vPosition;\n"
                       "in vec4 vTexCoord;\n"
                       "out vec4 texCoord;\n"
                       "uniform mat4 matrix;\n"
                       "void main() {\n"
                       "    texCoord = vTexCoord;\n"
                       "    gl_Position = matrix * vPosition;\n"
                       "}\n";
    QOpenGLShader* vsShader = new QOpenGLShader(QOpenGLShader::Vertex, this);
    vsShader->compileSourceCode(vsrc);
    /***********************************************************************************/
    const char* fsrc = "#version 130 core\n"
                       "uniform sampler2D tex;\n"
                       "in vec4 texCoord;\n"
                       "out vec4 fColor;\n"
                       "void main() {\n"
                       "    fColor = texture(tex, texCoord.st);\n"
                       "}\n";
    QOpenGLShader* fshader = new QOpenGLShader(QOpenGLShader::Fragment, this);
    fshader->compileSourceCode(fsrc);
    /***********************************************************************************/
    m_program = new QOpenGLShaderProgram;
    m_program->addShader(vsShader);
    m_program->addShader(fshader);
    m_program->link();
    m_program->bind();
}

void OpenGLWidget5::paintGL()
{
    int side = qMin(width(), height());
    glViewport((width() - side) / 2, (height() - side) / 2, side, side);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    //
    GLfloat vertices[2][4][3] = {
        {
            { -0.8f, 0.8f, 0.8f },
            { -0.8f, -0.8f, 0.8f },
            { 0.8f, -0.8f, 0.8f },
            { 0.8f, 0.8f, 0.8f }
        },
        {
            { 0.8f, 0.8f, 0.8f },
            { 0.8f, -0.8f, 0.8f },
            { 0.8f, -0.8f, -0.8f },
            { 0.8f, 0.8f, -0.8f }
        }
    };
    //
    m_buffer->create();
    m_buffer->bind();
    m_buffer->allocate(vertices, 48 * sizeof(GLfloat));
    //
    GLuint vPosition = m_program->attributeLocation("vPosition");
    m_program->setAttributeBuffer(vPosition, GL_FLOAT, 0, 3, 0);
    glEnableVertexAttribArray(vPosition);
    //
    GLfloat coords[2][4][2] = {
        {
            { 1.0f, 0.0f },
            { 0.0f, 1.0f },
            { 0.0f, 0.0f },
            { 1.0f, 1.0f }
        },
        {
            { 1.0f, 0.0f },
            { 0.0f, 1.0f },
            { 0.0f, 0.0f },
            { 1.0f, 1.0f }
        }
    };
    m_buffer->write(24 * sizeof(GLfloat), coords, 16 * sizeof(GLfloat));
    GLuint vTexCoord = m_program->attributeLocation("vTexCoord");
    m_program->setAttributeBuffer(vTexCoord, GL_FLOAT, 24 * sizeof(GLfloat), 2, 0);
    glEnableVertexAttribArray(vTexCoord);
    m_program->setUniformValue("tex", 0);
    //
    QMatrix4x4 matrix;
    matrix.perspective(45.0f, (GLfloat)width() / (GLfloat)height(), 0.1f, 100.0f);
    matrix.translate(0, 0, -3);
    matrix.rotate(-60, 0, 1, 0);
    m_program->setUniformValue("matrix", matrix);
    //
    for(int i = 0 ;i < 2; i++) {
        m_textures[i]->bind();
        glDrawArrays(GL_TRIANGLE_FAN, i * 4, 4);
    }
}