基于Qt的OpenGL学习（5）—— 坐标系统

要学习OpenGL的话，强烈安利这个教程JoeyDeVries的learnopengl，这里是中文翻译好的版本。教程中使用OpenGL是通过GLFW这个库，而在Qt中对OpenGL封装得很好，并且和GUI以及IO相关的处理Qt更便捷，学习起来更轻松。这里就对每篇教程，在Qt在分别直接使用OpenGL的函数和Qt封装好的类以作对比。
教程中使用的OpenGL版本为3.3，在Qt中需要使用此版本的OpenGL只需要继承类QOpenGLFunctions_3_3_Core即可。如果为了在不同设备上都能用OpenGL的话，Qt提供了类QOpenGLFunctions，这个类包含了大部分公共的函数，可能会有个别函数不能用。

对比说明

教程地址

原教程地址，相关知识可以点击链接学习。
我的工程地址，每篇教程一个commit，可以切换着看，查看本篇代码 git checkout v1.5，喜欢就点个Star吧~

不同点 (仅列出新增)

1. view、projection矩阵只需要初始化一次，就放到了initializeGL()中。
2. 原教程最中间的矩形不转是因为教程里循环赋值角度第0个时：angle = 0 * value。

运行结果

使用OpenGL函数版

CoreFunctionWidget.h

#ifndef COREFUNCTIONWIDGET_H
#define COREFUNCTIONWIDGET_H

#include <QOpenGLWidget>
#include <QOpenGLExtraFunctions>
#include <QOpenGLFunctions_3_3_Core>
#include <QOpenGLShader>
#include <QOpenGLShaderProgram>

class CoreFunctionWidget : public QOpenGLWidget
                           , protected /*QOpenGLExtraFunctions*/QOpenGLFunctions_3_3_Core
{
    Q_OBJECT
public:
    explicit CoreFunctionWidget(QWidget *parent = nullptr);
    ~CoreFunctionWidget();

protected:
    virtual void initializeGL();
    virtual void resizeGL(int w, int h);
    virtual void paintGL();

private:
    QOpenGLShaderProgram shaderProgram;

    QTimer* m_pTimer = nullptr;
    int     m_nTimeValue = 0;
};

#endif // COREFUNCTIONWIDGET_H

CoreFunctionWidget.cpp

#include "CoreFunctionWidget.h"
#include <QDebug>
#include <QTimer>

static GLuint VBO, VAO, texture1, texture2;

CoreFunctionWidget::CoreFunctionWidget(QWidget *parent) : QOpenGLWidget(parent)
{
    m_pTimer = new QTimer(this);
    connect(m_pTimer, &QTimer::timeout, this, [=]{
        m_nTimeValue += 1;
        update();
    });
    m_pTimer->start(40);
}

CoreFunctionWidget::~CoreFunctionWidget()
{
    glDeleteVertexArrays(1, &VAO);
    glDeleteBuffers(1, &VBO);
}

void CoreFunctionWidget::initializeGL(){
    this->initializeOpenGLFunctions();

    bool success = shaderProgram.addShaderFromSourceFile(QOpenGLShader::Vertex, ":/textures.vert");
    if (!success) {
        qDebug() << "shaderProgram addShaderFromSourceFile failed!" << shaderProgram.log();
        return;
    }

    success = shaderProgram.addShaderFromSourceFile(QOpenGLShader::Fragment, ":/textures.frag");
    if (!success) {
        qDebug() << "shaderProgram addShaderFromSourceFile failed!" << shaderProgram.log();
        return;
    }

    success = shaderProgram.link();
    if(!success) {
        qDebug() << "shaderProgram link failed!" << shaderProgram.log();
    }

    // configure global opengl state
    // -----------------------------
    glEnable(GL_DEPTH_TEST);

    //VAO，VBO data
    float vertices[] = {
        -0.5f, -0.5f, -0.5f,  0.0f, 0.0f,
         0.5f, -0.5f, -0.5f,  1.0f, 0.0f,
         0.5f,  0.5f, -0.5f,  1.0f, 1.0f,
         0.5f,  0.5f, -0.5f,  1.0f, 1.0f,
        -0.5f,  0.5f, -0.5f,  0.0f, 1.0f,
        -0.5f, -0.5f, -0.5f,  0.0f, 0.0f,

        -0.5f, -0.5f,  0.5f,  0.0f, 0.0f,
         0.5f, -0.5f,  0.5f,  1.0f, 0.0f,
         0.5f,  0.5f,  0.5f,  1.0f, 1.0f,
         0.5f,  0.5f,  0.5f,  1.0f, 1.0f,
        -0.5f,  0.5f,  0.5f,  0.0f, 1.0f,
        -0.5f, -0.5f,  0.5f,  0.0f, 0.0f,

        -0.5f,  0.5f,  0.5f,  1.0f, 0.0f,
        -0.5f,  0.5f, -0.5f,  1.0f, 1.0f,
        -0.5f, -0.5f, -0.5f,  0.0f, 1.0f,
        -0.5f, -0.5f, -0.5f,  0.0f, 1.0f,
        -0.5f, -0.5f,  0.5f,  0.0f, 0.0f,
        -0.5f,  0.5f,  0.5f,  1.0f, 0.0f,

         0.5f,  0.5f,  0.5f,  1.0f, 0.0f,
         0.5f,  0.5f, -0.5f,  1.0f, 1.0f,
         0.5f, -0.5f, -0.5f,  0.0f, 1.0f,
         0.5f, -0.5f, -0.5f,  0.0f, 1.0f,
         0.5f, -0.5f,  0.5f,  0.0f, 0.0f,
         0.5f,  0.5f,  0.5f,  1.0f, 0.0f,

        -0.5f, -0.5f, -0.5f,  0.0f, 1.0f,
         0.5f, -0.5f, -0.5f,  1.0f, 1.0f,
         0.5f, -0.5f,  0.5f,  1.0f, 0.0f,
         0.5f, -0.5f,  0.5f,  1.0f, 0.0f,
        -0.5f, -0.5f,  0.5f,  0.0f, 0.0f,
        -0.5f, -0.5f, -0.5f,  0.0f, 1.0f,

        -0.5f,  0.5f, -0.5f,  0.0f, 1.0f,
         0.5f,  0.5f, -0.5f,  1.0f, 1.0f,
         0.5f,  0.5f,  0.5f,  1.0f, 0.0f,
         0.5f,  0.5f,  0.5f,  1.0f, 0.0f,
        -0.5f,  0.5f,  0.5f,  0.0f, 0.0f,
        -0.5f,  0.5f, -0.5f,  0.0f, 1.0f
    };

    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);
    // bind the Vertex Array Object first, then bind and set vertex buffer(s), and then configure vertex attributes(s).
    glBindVertexArray(VAO);

    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    // position attribute
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 5 * sizeof(float), (void*)0);
    glEnableVertexAttribArray(0);
    // texture coord attribute
    glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 5 * sizeof(float), (void*)(3 * sizeof(float)));
    glEnableVertexAttribArray(1);

    // texture 1
    // ---------
    glGenTextures(1, &texture1);
    glBindTexture(GL_TEXTURE_2D, texture1);
     // set the texture wrapping parameters
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);   // set texture wrapping to GL_REPEAT (default wrapping method)
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
    // set texture filtering parameters
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    // load image, create texture and generate mipmaps
    QImage img1 = QImage(":/container.jpg").convertToFormat(QImage::Format_RGB888);
    if (!img1.isNull()) {
        glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, img1.width(), img1.height(), 0, GL_RGB, GL_UNSIGNED_BYTE, img1.bits());
        glGenerateMipmap(GL_TEXTURE_2D);
    }

    // texture 2
    // ---------
    glGenTextures(1, &texture2);
    glBindTexture(GL_TEXTURE_2D, texture2);
    // set the texture wrapping parameters
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);   // set texture wrapping to GL_REPEAT (default wrapping method)
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
    // set texture filtering parameters
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    // load image, create texture and generate mipmaps
    QImage img2 = QImage(":/awesomeface.png").convertToFormat(QImage::Format_RGBA8888).mirrored(true, true);
    if (!img2.isNull()) {
        // note that the awesomeface.png has transparency and thus an alpha channel, so make sure to tell OpenGL the data type is of GL_RGBA
        glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, img2.width(), img2.height(), 0, GL_RGBA, GL_UNSIGNED_BYTE, img2.bits());
        glGenerateMipmap(GL_TEXTURE_2D);
    }

    shaderProgram.bind();   // don't forget to activate/use the shader before setting uniforms!
    // tell opengl for each sampler to which texture unit it belongs to (only has to be done once)
    shaderProgram.setUniformValue("texture1", 0);
    shaderProgram.setUniformValue("texture2", 1);
    // note: currently we set the projection matrix each frame, but since the projection matrix rarely changes it's often best practice to set it outside the main loop only once.
    QMatrix4x4 view;
    view.translate(QVector3D(0.0f, 0.0f, -3.0f));
    shaderProgram.setUniformValue("view", view);
    QMatrix4x4 projection;
    projection.perspective(45.0f, 1.0f * width() / height(), 0.1f, 100.0f);
    shaderProgram.setUniformValue("projection", projection);
    shaderProgram.release();
}

void CoreFunctionWidget::resizeGL(int w, int h){
    glViewport(0, 0, w, h);
}


static QVector3D cubePositions[] = {
  QVector3D( 0.0f,  0.0f,  0.0f),
  QVector3D( 2.0f,  5.0f, -15.0f),
  QVector3D(-1.5f, -2.2f, -2.5f),
  QVector3D(-3.8f, -2.0f, -12.3f),
  QVector3D( 2.4f, -0.4f, -3.5f),
  QVector3D(-1.7f,  3.0f, -7.5f),
  QVector3D( 1.3f, -2.0f, -2.5f),
  QVector3D( 1.5f,  2.0f, -2.5f),
  QVector3D( 1.5f,  0.2f, -1.5f),
  QVector3D(-1.3f,  1.0f, -1.5f)
};

void CoreFunctionWidget::paintGL(){
    glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // also clear the depth buffer now!

    // bind textures on corresponding texture units
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, texture1);
    glActiveTexture(GL_TEXTURE1);
    glBindTexture(GL_TEXTURE_2D, texture2);

    shaderProgram.bind();
    // render boxes
    glBindVertexArray(VAO);
    for (unsigned int i = 0; i < 10; i++) {
       // calculate the model matrix for each object and pass it to shader before drawing
       QMatrix4x4 model;
       model.translate(cubePositions[i]);
       float angle = (i + 1.0f) * m_nTimeValue;
       model.rotate(angle, QVector3D(1.0f, 0.3f, 0.5f));
       shaderProgram.setUniformValue("model", model);
       glDrawArrays(GL_TRIANGLES, 0, 36);
    }

    shaderProgram.release();
}

使用Qt相关函数版

QtFunctionWidget.h

#ifndef QTFUNCTIONWIDGET_H
#define QTFUNCTIONWIDGET_H

#include <QOpenGLWidget>


#include <QOpenGLWidget>
#include <QOpenGLShader>
#include <QOpenGLShaderProgram>
#include <QOpenGLFunctions>
#include <QOpenGLVertexArrayObject>
#include <QOpenGLBuffer>
#include <QOpenGLTexture>

class QtFunctionWidget : public QOpenGLWidget, protected QOpenGLFunctions
{
public:
    QtFunctionWidget(QWidget *parent = nullptr);
    ~QtFunctionWidget() Q_DECL_OVERRIDE;

protected:
    virtual void initializeGL() Q_DECL_OVERRIDE;
    virtual void resizeGL(int w, int h) Q_DECL_OVERRIDE;
    virtual void paintGL() Q_DECL_OVERRIDE;

private:
    QOpenGLShaderProgram shaderProgram;
    QOpenGLBuffer vbo;
    QOpenGLVertexArrayObject vao;
    QOpenGLTexture *texture1 = nullptr;
    QOpenGLTexture *texture2 = nullptr;

    QTimer* m_pTimer = nullptr;
    int     m_nTimeValue = 0;
};

#endif // QTFUNCTIONWIDGET_H

QtFunctionWidget.cpp

#include "QtFunctionWidget.h"
#include <QDebug>
#include <QTimer>

QtFunctionWidget::QtFunctionWidget(QWidget *parent) : QOpenGLWidget (parent),
    vbo(QOpenGLBuffer::VertexBuffer)
{
    m_pTimer = new QTimer(this);
    connect(m_pTimer, &QTimer::timeout, this, [=]{
        m_nTimeValue += 1;
        update();
    });
    m_pTimer->start(40);
}

QtFunctionWidget::~QtFunctionWidget(){
    makeCurrent();

    vbo.destroy();
    vao.destroy();

    delete texture1;
    delete texture2;

    doneCurrent();
}

void QtFunctionWidget::initializeGL(){
    this->initializeOpenGLFunctions();

    bool success = shaderProgram.addShaderFromSourceFile(QOpenGLShader::Vertex, ":/textures.vert");
    if (!success) {
        qDebug() << "shaderProgram addShaderFromSourceFile failed!" << shaderProgram.log();
        return;
    }

    success = shaderProgram.addShaderFromSourceFile(QOpenGLShader::Fragment, ":/textures.frag");
    if (!success) {
        qDebug() << "shaderProgram addShaderFromSourceFile failed!" << shaderProgram.log();
        return;
    }

    success = shaderProgram.link();
    if(!success) {
        qDebug() << "shaderProgram link failed!" << shaderProgram.log();
    }

    // configure global opengl state
    // -----------------------------
    glEnable(GL_DEPTH_TEST);

    //VAO，VBO data
    float vertices[] = {
        -0.5f, -0.5f, -0.5f,  0.0f, 0.0f,
         0.5f, -0.5f, -0.5f,  1.0f, 0.0f,
         0.5f,  0.5f, -0.5f,  1.0f, 1.0f,
         0.5f,  0.5f, -0.5f,  1.0f, 1.0f,
        -0.5f,  0.5f, -0.5f,  0.0f, 1.0f,
        -0.5f, -0.5f, -0.5f,  0.0f, 0.0f,

        -0.5f, -0.5f,  0.5f,  0.0f, 0.0f,
         0.5f, -0.5f,  0.5f,  1.0f, 0.0f,
         0.5f,  0.5f,  0.5f,  1.0f, 1.0f,
         0.5f,  0.5f,  0.5f,  1.0f, 1.0f,
        -0.5f,  0.5f,  0.5f,  0.0f, 1.0f,
        -0.5f, -0.5f,  0.5f,  0.0f, 0.0f,

        -0.5f,  0.5f,  0.5f,  1.0f, 0.0f,
        -0.5f,  0.5f, -0.5f,  1.0f, 1.0f,
        -0.5f, -0.5f, -0.5f,  0.0f, 1.0f,
        -0.5f, -0.5f, -0.5f,  0.0f, 1.0f,
        -0.5f, -0.5f,  0.5f,  0.0f, 0.0f,
        -0.5f,  0.5f,  0.5f,  1.0f, 0.0f,

         0.5f,  0.5f,  0.5f,  1.0f, 0.0f,
         0.5f,  0.5f, -0.5f,  1.0f, 1.0f,
         0.5f, -0.5f, -0.5f,  0.0f, 1.0f,
         0.5f, -0.5f, -0.5f,  0.0f, 1.0f,
         0.5f, -0.5f,  0.5f,  0.0f, 0.0f,
         0.5f,  0.5f,  0.5f,  1.0f, 0.0f,

        -0.5f, -0.5f, -0.5f,  0.0f, 1.0f,
         0.5f, -0.5f, -0.5f,  1.0f, 1.0f,
         0.5f, -0.5f,  0.5f,  1.0f, 0.0f,
         0.5f, -0.5f,  0.5f,  1.0f, 0.0f,
        -0.5f, -0.5f,  0.5f,  0.0f, 0.0f,
        -0.5f, -0.5f, -0.5f,  0.0f, 1.0f,

        -0.5f,  0.5f, -0.5f,  0.0f, 1.0f,
         0.5f,  0.5f, -0.5f,  1.0f, 1.0f,
         0.5f,  0.5f,  0.5f,  1.0f, 0.0f,
         0.5f,  0.5f,  0.5f,  1.0f, 0.0f,
        -0.5f,  0.5f,  0.5f,  0.0f, 0.0f,
        -0.5f,  0.5f, -0.5f,  0.0f, 1.0f
    };

    QOpenGLVertexArrayObject::Binder vaoBind(&vao);

    vbo.create();
    vbo.bind();
    vbo.allocate(vertices, sizeof(vertices));

    // position attribute
    int attr = -1;
    attr = shaderProgram.attributeLocation("aPos");
    shaderProgram.setAttributeBuffer(attr, GL_FLOAT, 0, 3, sizeof(GLfloat) * 5);
    shaderProgram.enableAttributeArray(attr);
    // texture coord attribute
    attr = shaderProgram.attributeLocation("aTexCoord");
    shaderProgram.setAttributeBuffer(attr, GL_FLOAT, sizeof(GLfloat) * 3, 2, sizeof(GLfloat) * 5);
    shaderProgram.enableAttributeArray(attr);

    // texture 1
    // ---------
    texture1 = new QOpenGLTexture(QImage(":/container.jpg"), QOpenGLTexture::GenerateMipMaps);
    if(!texture1->isCreated()){
        qDebug() << "Failed to load texture";
    }
    // set the texture wrapping parameters
    texture1->setWrapMode(QOpenGLTexture::DirectionS, QOpenGLTexture::Repeat);
    texture1->setWrapMode(QOpenGLTexture::DirectionT, QOpenGLTexture::Repeat);
    // set texture filtering parameters
    texture1->setMinificationFilter(QOpenGLTexture::Linear);
    texture1->setMagnificationFilter(QOpenGLTexture::Linear);

    // texture 2
    // ---------
    texture2 = new QOpenGLTexture(QImage(":/awesomeface.png").mirrored(true, true), QOpenGLTexture::GenerateMipMaps);
    if(!texture2->isCreated()){
        qDebug() << "Failed to load texture";
    }
    // set the texture wrapping parameters
    texture2->setWrapMode(QOpenGLTexture::DirectionS, QOpenGLTexture::Repeat);
    texture2->setWrapMode(QOpenGLTexture::DirectionT, QOpenGLTexture::Repeat);
    // set texture filtering parameters
    texture2->setMinificationFilter(QOpenGLTexture::Linear);
    texture1->setMagnificationFilter(QOpenGLTexture::Linear);

    // tell opengl for each sampler to which texture unit it belongs to (only has to be done once)
    shaderProgram.bind();   // don't forget to activate/use the shader before setting uniforms!
    shaderProgram.setUniformValue("texture1", 0);
    shaderProgram.setUniformValue("texture2", 1);
    // note: currently we set the projection matrix each frame, but since the projection matrix rarely changes it's often best practice to set it outside the main loop only once.
    QMatrix4x4 view;
    view.translate(QVector3D(0.0f, 0.0f, -3.0f));
    shaderProgram.setUniformValue("view", view);
    QMatrix4x4 projection;
    projection.perspective(45.0f, 1.0f * width() / height(), 0.1f, 100.0f);
    shaderProgram.setUniformValue("projection", projection);
    shaderProgram.release();

    vbo.release();
}

void QtFunctionWidget::resizeGL(int w, int h){
    glViewport(0, 0, w, h);
}

static QVector3D cubePositions[] = {
  QVector3D( 0.0f,  0.0f,  0.0f),
  QVector3D( 2.0f,  5.0f, -15.0f),
  QVector3D(-1.5f, -2.2f, -2.5f),
  QVector3D(-3.8f, -2.0f, -12.3f),
  QVector3D( 2.4f, -0.4f, -3.5f),
  QVector3D(-1.7f,  3.0f, -7.5f),
  QVector3D( 1.3f, -2.0f, -2.5f),
  QVector3D( 1.5f,  2.0f, -2.5f),
  QVector3D( 1.5f,  0.2f, -1.5f),
  QVector3D(-1.3f,  1.0f, -1.5f)
};

void QtFunctionWidget::paintGL(){
    glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // also clear the depth buffer now!

    // bind textures on corresponding texture units
    glActiveTexture(GL_TEXTURE0);
    texture1->bind();
    glActiveTexture(GL_TEXTURE1);
    texture2->bind();

    shaderProgram.bind();

    {// render box
        QOpenGLVertexArrayObject::Binder vaoBind(&vao);

        for (unsigned int i = 0; i < 10; i++) {
           // calculate the model matrix for each object and pass it to shader before drawing
           QMatrix4x4 model;
           model.translate(cubePositions[i]);
           float angle = (i + 1.0f) * m_nTimeValue;
           model.rotate(angle, QVector3D(1.0f, 0.3f, 0.5f));
           shaderProgram.setUniformValue("model", model);
           glDrawArrays(GL_TRIANGLES, 0, 36);
        }
    }

    texture1->release();
    texture2->release();
    shaderProgram.release();
}

GLSL

textures.vert

#version 330 core
layout (location = 0) in vec3 aPos;
layout (location = 1) in vec2 aTexCoord;

out vec2 TexCoord;

uniform mat4 model;
uniform mat4 view;
uniform mat4 projection;

void main(){
  gl_Position = projection * view * model * vec4(aPos, 1.0f);
  TexCoord = aTexCoord;
}

textures.frag

#version 330 core
out vec4 FragColor;

in vec2 TexCoord;

uniform sampler2D texture1;
uniform sampler2D texture2;

void main()
{
    FragColor = mix(texture2D(texture1, TexCoord), texture2D(texture2, TexCoord), 0.2f);
}

main.cpp

#include <QApplication>
#include "QtFunctionWidget.h"
#include "CoreFunctionWidget.h"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QtFunctionWidget w1;
    CoreFunctionWidget w2;

    w1.setWindowTitle(QObject::tr("QtFunction"));
    w2.setWindowTitle(QObject::tr("CoreFunction"));

    w1.show();
    w2.show();

    return a.exec();
}