基于Qt的OpenGL编程（3.x以上GLSL可编程管线版）---(二)你好，三角形_QOpenGLExtraFunctions版

本篇文章，是一项带引号的“翻译”类型文章。Joey De Vries  的现代OpenGL教程是我看过最好的图形学教程，没有之一。奈何原作者是在Visual Studio平台进行开发，针对GUI和OpenGL的结合，没有多言。在自己实际开发应用中，没有好的GUI确是造成不少困扰，故我欲作为一名搬运工，将Vries大神的代码进行Qt平台的“移植”。预了解代码中关于OpenGL函数的详细解释，请看Vries的教程，连接如下。(这是此篇教程的原地址https://learnopengl-cn.github.io/01%20Getting%20started/04%20Hello%20Triangle/)本篇目的是创立窗口，生成三角形，如下图所示。


Qt对OpenGL的支持，要求，必须public继承QOpenGLWidget类，然后重写[b]这三个函数。[/b]


这里介绍第一种方法，继承QOpenGLExtraFunction为了使用glShaderSource()这种OpenGL成员函数，要求必须proteced继承QOpenGLFunctions类，或QOpenGLExtraFunctions类，这里选择继承QOpenGLExtraFunctions类，因为这个类是QOpenGLFunctions类的子类，多了glGenVertexArrays(1, &VAO)这一函数。项目组织结构如下：


widget.h如下#ifndef WIDGET_H
#define WIDGET_H

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

class Triangle : public QOpenGLWidget, protected QOpenGLExtraFunctions
{
public:
Triangle();
~Triangle();
protected:
virtual void initializeGL();
virtual void resizeGL(int w, int h);
virtual void paintGL();
private:
GLuint shaderProgram;
};

#endif // WIDGET_H
widget.cpp如下#include "widget.h"
GLuint VBO, VAO;
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, 1.0);\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";
Triangle::Triangle(){

}

Triangle::~Triangle(){

}

void Triangle::initializeGL(){

//着色器部分
this->initializeOpenGLFunctions();
//core = QOpenGLContext::currentContext()->versionFunctions<QOpenGLFunctions_3_3_Core>();
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 << endl;
}

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 << endl;
}
shaderProgram = glCreateProgram();
glAttachShader(shaderProgram, vertexShader);
glAttachShader(shaderProgram, fragmentShader);
glLinkProgram(shaderProgram);

glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
if (!success) {
glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);
qDebug() << "ERROR::SHADER::PROGRAM::LINKING_FAILED\n" << infoLog << endl;
}
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);//两个参数，第一个为需要创建的缓存数量。第二个为用于存储单一ID或多个ID的GLuint变量或数组的地址
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 Triangle::resizeGL(int w, int h){
glViewport(0, 0, w, h);
}

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

glUseProgram(shaderProgram);
glBindVertexArray(VAO);
glDrawArrays(GL_TRIANGLES, 0, 3);
glUseProgram(0);
}main函数如下#include "widget.h"
#include <QApplication>

int main(int argc, char *argv[])
{
QApplication a(argc, argv);
Triangle t;
t.show();

return a.exec();
}在继承QOpenGLExtraFunctions的情形下，整个Vries的代码可以在基本无改动的情况下，直接移植。