[C++知识库]Qt-OpenGL-01 hello三角形

具体参考：你好，三角形 - LearnOpenGL CN

先上完整的学习代码：

#include <glad/glad.h>
#include <GLFW/glfw3.h>

#include <iostream>

void framebuffer_size_callback(GLFWwindow* window, int width, int height);
void processInput(GLFWwindow *window);

// settings
const unsigned int SCR_WIDTH = 800;
const unsigned int SCR_HEIGHT = 600;

const char *vertexShaderSource = "#version 330 core\n"
    "layout (location = 0) in vec3 aPos;\n"
    "void main()\n"
    "{\n"
    "   gl_Position = vec4(aPos.x, aPos.y, aPos.z, 1.0);\n"
    "}\0";
const char *fragmentShaderSource = "#version 330 core\n"
    "out vec4 FragColor;\n"
    "void main()\n"
    "{\n"
    "   FragColor = vec4(1.0f, 0.5f, 0.2f, 1.0f);\n"
    "}\n\0";

int main()
{
    // glfw: initialize and configure
    // ------------------------------
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

#ifdef __APPLE__
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
#endif

    // glfw window creation
    // --------------------
    GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", NULL, NULL);
    if (window == NULL)
    {
        std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate();
        return -1;
    }
    glfwMakeContextCurrent(window);
    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);

    // glad: load all OpenGL function pointers
    // ---------------------------------------
    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
    {
        std::cout << "Failed to initialize GLAD" << std::endl;
        return -1;
    }


    // build and compile our shader program
    // ------------------------------------
    // vertex shader
    unsigned int vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
    glCompileShader(vertexShader);
    // check for shader compile errors
    int success;
    char infoLog[512];
    glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
    if (!success)
    {
        glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << std::endl;
    }
    // fragment shader
    unsigned int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
    glCompileShader(fragmentShader);
    // check for shader compile errors
    glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
    if (!success)
    {
        glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << std::endl;
    }
    // link shaders
    unsigned int shaderProgram = glCreateProgram();
    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, fragmentShader);
    glLinkProgram(shaderProgram);
    // check for linking errors
    glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
    if (!success) {
        glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::PROGRAM::LINKING_FAILED\n" << infoLog << std::endl;
    }
    glDeleteShader(vertexShader);
    glDeleteShader(fragmentShader);

    // set up vertex data (and buffer(s)) and configure vertex attributes
    // ------------------------------------------------------------------
    float vertices[] = {
        -0.5f, -0.5f, 0.0f, // left  
         0.5f, -0.5f, 0.0f, // right 
         0.0f,  0.5f, 0.0f  // top   
    }; 

    unsigned int VBO, VAO;
    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);

    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
    glEnableVertexAttribArray(0);

    // note that this is allowed, the call to glVertexAttribPointer registered VBO as the vertex attribute's bound vertex buffer object so afterwards we can safely unbind
    glBindBuffer(GL_ARRAY_BUFFER, 0); 

    // You can unbind the VAO afterwards so other VAO calls won't accidentally modify this VAO, but this rarely happens. Modifying other
    // VAOs requires a call to glBindVertexArray anyways so we generally don't unbind VAOs (nor VBOs) when it's not directly necessary.
    glBindVertexArray(0); 


    // uncomment this call to draw in wireframe polygons.
    glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);

    // render loop
    // -----------
    while (!glfwWindowShouldClose(window))
    {
        // input
        // -----
        processInput(window);

        // render
        // ------
        glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);

        // draw our first triangle
        glUseProgram(shaderProgram);
        glBindVertexArray(VAO); // seeing as we only have a single VAO there's no need to bind it every time, but we'll do so to keep things a bit more organized
        glDrawArrays(GL_TRIANGLES, 0, 3);
        // glBindVertexArray(0); // no need to unbind it every time 
 
        // glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
        // -------------------------------------------------------------------------------
        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    // optional: de-allocate all resources once they've outlived their purpose:
    // ------------------------------------------------------------------------
    glDeleteVertexArrays(1, &VAO);
    glDeleteBuffers(1, &VBO);
    glDeleteProgram(shaderProgram);

    // glfw: terminate, clearing all previously allocated GLFW resources.
    // ------------------------------------------------------------------
    glfwTerminate();
    return 0;
}

// process all input: query GLFW whether relevant keys are pressed/released this frame and react accordingly
// ---------------------------------------------------------------------------------------------------------
void processInput(GLFWwindow *window)
{
    if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
        glfwSetWindowShouldClose(window, true);
}

// glfw: whenever the window size changed (by OS or user resize) this callback function executes
// ---------------------------------------------------------------------------------------------
void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{
    // make sure the viewport matches the new window dimensions; note that width and 
    // height will be significantly larger than specified on retina displays.
    glViewport(0, 0, width, height);
}

代码所占边幅可能有点长，但是这是学习opengl最重要的一步，有种麻雀虽小但五脏俱全的意思，编译完成，运行没有问题就会得到以下界面：恭喜自己

?大概流程为：初始化glfw->创造一个GLFWWindow的窗口->给窗口绑定一个Context->

加载glad的所有函数指针->绑定顶点着色器vertex shader和片段着色器fragment shader到

shaderProgram中->绑定shader->检查shader链接->

// 1. 绑定VAO glBindVertexArray(VAO);

// 2. 把顶点数组复制到缓冲中供OpenGL使用 glBindBuffer(GL_ARRAY_BUFFER, VBO); glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

// 3. 设置顶点属性指针 glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0); glEnableVertexAttribArray(0);

->在while里绘制（glUseProgram(shaderProgram);
? ? ????????????????????????????????glBindVertexArray(VAO);?
? ? ? ????????????????????????? glDrawArrays(GL_TRIANGLES, 0, 3);）

绘制三角形结束。

以下搭建一个简单的qt的工程，用来方便学习时，敲代码。本文章主要以代码为主，后面将代码会整理到GitHub。工程结构：

//main.cpp
#include "mainwindow.h"

#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    return a.exec();
}

//MainWindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();

private:
    Ui::MainWindow *ui;
    QWidget *m_contentWidget = nullptr;
};
#endif // MAINWINDOW_H

//MainWindow.cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"

#include "Defines.h"
#include "WidgetFactory.h"

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    m_contentWidget = WidgetFactory::GetWidgetFactory(WidgetClass::triangle_widget , this);
    ui->verticalLayout->addWidget(m_contentWidget);
}

MainWindow::~MainWindow()
{
    delete ui;
}

//简单的工厂类，方便切界面?

#pragma once

#include <qwidget.h>

#include "Defines.h"
#include "trianglewidget.h"


class WidgetFactory
{

public:
    WidgetFactory()
    {

    }

    static QWidget *GetWidgetFactory(WidgetClass type,QWidget *parent){
        if(type == WidgetClass::triangle_widget)
        {
            return new TriangleWidget(parent);
        }

        return new QWidget();
    }

};


//Defines.h

#pragma once

enum WidgetClass
{
    triangle_widget = 0
};

????????接下来是渲染三角形的类。在这里首先得感谢? HELLO_IHAD大佬，也是看到他得博客受到启发，决定用qt跟着学习，并且客户端开发很多时候还是就用qt作为UI库，所以就这么干了。

关于qt怎么渲染一个3d窗口，有很多种写法：

以下采用public QOpenGLWidget,protected QOpenGLExtraFunctions的方式，因为这样做可以无缝使用LearnOpenGL的教程源码。强烈建议是在学习LearnOpenGL CN?之后弄清楚OpenGL后再去看Qt的用法。费不多说，搞。

首先需要在我们的自己的类里，重写以下三个方法：

?QOpenGLWidget就替代了教程中的GLFW.

以下为triangle类：

#pragma once

#include <QWidget>

#include <QOpenGLWidget>
#include <QOpenGLExtraFunctions>
#include <QDebug>

namespace Ui {
class TriangleWidget;
}

class HelloTriangle;

class TriangleWidget : public QWidget
{
    Q_OBJECT

public:
    explicit TriangleWidget(QWidget *parent = nullptr);
    ~TriangleWidget();

private:
    Ui::TriangleWidget *ui;
    HelloTriangle *m_contentWidget;
};


class HelloTriangle : public QOpenGLWidget,protected QOpenGLExtraFunctions
{

public:
    HelloTriangle(){};
    ~HelloTriangle(){};
protected:
    virtual void initializeGL();
    virtual void resizeGL(int w, int h);
    virtual void paintGL();
private:
    QOpenGLShaderProgram m_shaderProgram;

};


//cpp

#include "trianglewidget.h"
#include "ui_trianglewidget.h"

TriangleWidget::TriangleWidget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::TriangleWidget)
{
    ui->setupUi(this);
    m_contentWidget = new HelloTriangle();
    ui->verticalLayout->addWidget(m_contentWidget);
}

TriangleWidget::~TriangleWidget()
{
    delete ui;
}

const char *vertexShaderSource =
        "#version 330 core\n"
        "layout(location = 0) in vec3 aPos;\n"
        "void main(){\n"
        "  gl_Position = vec4(aPos.x, aPos.y, aPos.z, 1.0f);\n"
        "}\n\0";
const char *fragmentShaderSource =
        "#version 330 core\n"
        "out vec4 FragColor;\n"
        "void main(){\n"
        "   FragColor = vec4(1.0f, 0.5f, 0.2f, 1.0f);\n"
        "}\n\0";


GLuint VBO, VAO;

void HelloTriangle::initializeGL()
{
    //初始化functions
    this->initializeOpenGLFunctions();
    //顶点这色器
    int vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
    glCompileShader(vertexShader);

    int success;
    char infoLog[512];
    glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
    if (!success)
    {
        glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
        qDebug() << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog ;
    }

    //片段着色器
    int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
    glCompileShader(fragmentShader);

    glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
    if (!success)
    {
        glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);
        qDebug() << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog;
    }
    m_shaderProgramId = glCreateProgram();
    //附加以上两个着色器
    glAttachShader(m_shaderProgramId, vertexShader);
    glAttachShader(m_shaderProgramId, fragmentShader);
    //链接
    glLinkProgram(m_shaderProgramId);

    //检测是否链接成功
    glGetProgramiv(m_shaderProgramId, GL_LINK_STATUS, &success);
    if (!success) {
        glGetProgramInfoLog(m_shaderProgramId, 512, NULL, infoLog);
        qDebug() << "ERROR::SHADER::PROGRAM::LINKING_FAILED\n" << infoLog;
    }
    glDeleteShader(vertexShader);
    glDeleteShader(fragmentShader);

    //VAO，VBO数据部分
    GLfloat vertices[] = {
        -0.5f, -0.5f, 0.0f, // left
        0.5f, -0.5f, 0.0f, // right
        0.0f,  0.5f, 0.0f  // top
    };

    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);
    glBindVertexArray(VAO);
    glBindBuffer(GL_ARRAY_BUFFER, VBO);

    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), (void*)0);
    glEnableVertexAttribArray(0);

    glBindBuffer(GL_ARRAY_BUFFER, 0);
    glBindVertexArray(0);
}

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

void HelloTriangle::paintGL()
{
    glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT);

    //使用着色器程序
    glUseProgram(m_shaderProgramId);
    glBindVertexArray(VAO);
    glDrawArrays(GL_TRIANGLES, 0, 3);
    glUseProgram(0);
}