基于Qt的OpenGL编程（3.x以上GLSL可编程管线版）---(五)变换

本篇目的是在学习着色器中uniform类型变量的传值，和QMatrix4*4矩阵的应用，掌握最基本的translate，scale，rotate矩阵操作。

（Vries的原教程地址如下，https://learnopengl-cn.github.io/01%20Getting%20started/07%20Transformations/ 关于函数的具体解析及OpenGL中的矩阵变换思想请看这个教程，本篇旨在对Vires思想做Qt平台的移植）

将上一个纹理教程的图片作移动，旋转操作，如下图所示。

在Vries教程中，实现此功能的核心代码，仅6行，生成矩阵，移动旋转矩阵。放在while循环不停更新即可。

现在让我们在Qt环境下实现这个功能，首先是对于glfwGetTime()这个函数。这个函数是在glfw.h头文件里，qt的核心模式里没有这个函数。使用Qtime类对象代替之。查阅函数解析，说明返回的是秒s，但实际应用上，感觉返回的应该是毫秒ms。

同时，qt对绘图函数paintGL()是只绘一次的，所以需在paintGL()中增添函数update（），更新绘图函数。

源代码如下，较上篇教程代码修改widget.h,widget.cpp与vertexshadersource.vert文件，修改部分见注释

widget.h

#ifndef WIDGET_H
#define WIDGET_H

#include <QOpenGLWidget>
#include <QDebug>
#include <QOpenGLFunctions_3_3_Core>
#include "shader.h"
#include <QOpenGLTexture>
#include <QTime>    //增添头文件

class Triangle : public QOpenGLWidget
{
public:
    Triangle();
    GLuint a;
    ~Triangle();
protected:
    virtual void initializeGL();
    virtual void resizeGL(int w, int h);
    virtual void paintGL();
private:
    Shader *ourShader;
    QOpenGLTexture *texture1;
    QOpenGLTexture *texture2;

    QOpenGLFunctions_3_3_Core *core;
    QTime time; //增添QTime对象，替代glfwGetTime()函数
};

#endif // WIDGET_H

widget.cpp

#include "widget.h"
GLuint VBO, VAO, EBO;

Triangle::Triangle(){
    this->setWindowTitle("Texture");
}

Triangle::~Triangle(){
    delete ourShader;
    core->glDeleteVertexArrays(1, &VAO);
    core->glDeleteBuffers(1, &VBO);
    core->glDeleteBuffers(1, &EBO);
    texture1->destroy();
    texture2->destroy();
}

void Triangle::initializeGL(){

    //着色器部分
    core = QOpenGLContext::currentContext()->versionFunctions<QOpenGLFunctions_3_3_Core>();
    ourShader = new Shader(":/shaders/vertexshadersource.vert", ":/shaders/fragmentshadersource.frag");

    //VAO，VBO数据部分
    GLfloat vertices[] = {
        0.5f,  0.5f, 0.0f,   1.0f, 0.0f, 0.0f,   1.0f, 1.0f, // top right
        0.5f, -0.5f, 0.0f,   0.0f, 1.0f, 0.0f,   1.0f, 0.0f, // bottom right
       -0.5f, -0.5f, 0.0f,   0.0f, 0.0f, 1.0f,   0.0f, 0.0f, // bottom left
       -0.5f,  0.5f, 0.0f,   1.0f, 1.0f, 0.0f,   0.0f, 1.0f  // top left
    };

    GLuint indices[] = {
        0, 1, 3, // first triangle
        1, 2, 3  // second triangle
    };

    core->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
    core->glGenBuffers(1, &VBO);
    core->glGenBuffers(1, &EBO);

    core->glBindVertexArray(VAO);

    core->glBindBuffer(GL_ARRAY_BUFFER, VBO);
    core->glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    core->glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
    core->glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);

    core->glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)0);
    core->glEnableVertexAttribArray(0);
    // color attribute
    core->glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(3 * sizeof(float)));
    core->glEnableVertexAttribArray(1);
    // texture coord attribute
    core->glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(6 * sizeof(float)));
    core->glEnableVertexAttribArray(2);

    //纹理
    //第一张箱子
    texture1 = new QOpenGLTexture(QImage(":/textures/res/textures/container.jpg").mirrored(), QOpenGLTexture::GenerateMipMaps); //直接生成绑定一个2d纹理, 并生成多级纹理MipMaps
    if(!texture1->isCreated()){
        qDebug() << "Failed to load texture" << endl;
    }
    texture1->setWrapMode(QOpenGLTexture::DirectionS, QOpenGLTexture::Repeat);// 等于glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    texture1->setWrapMode(QOpenGLTexture::DirectionT, QOpenGLTexture::Repeat);//    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);

    texture1->setMinificationFilter(QOpenGLTexture::Linear);   //等价于glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    texture1->setMagnificationFilter(QOpenGLTexture::Linear);  //     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);


    //第二张笑脸
    texture2 = new QOpenGLTexture(QImage(":/textures/res/textures/smile.png").mirrored(), QOpenGLTexture::GenerateMipMaps); //直接生成绑定一个2d纹理, 并生成多级纹理MipMaps
    if(!texture2->isCreated()){
        qDebug() << "Failed to load texture" << endl;
    }
    texture2->setWrapMode(QOpenGLTexture::DirectionS, QOpenGLTexture::Repeat);// 等于glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    texture2->setWrapMode(QOpenGLTexture::DirectionT, QOpenGLTexture::Repeat);//    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);

    texture2->setMinificationFilter(QOpenGLTexture::Linear);   //等价于glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    texture2->setMagnificationFilter(QOpenGLTexture::Linear);  //     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

    //设置纹理单元编号
    ourShader->use();
    ourShader->shaderProgram->setUniformValue(ourShader->shaderProgram->uniformLocation("texture1"), 0);//等价于ourShader.setInt("texture1", 0) setInt函数，是Vries自写的函数，实际应用还是要先获取“texture1”的location，然后设值
    ourShader->shaderProgram->setUniformValue(ourShader->shaderProgram->uniformLocation("texture2"), 1);

    core->glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
    time.start();//开启计时器，返回毫秒
}

void Triangle::resizeGL(int w, int h){
    core->glViewport(0, 0, w, h);
}

void Triangle::paintGL(){
    core->glClear(GL_COLOR_BUFFER_BIT);

    core->glActiveTexture(GL_TEXTURE0);
    texture1->bind();
    core->glActiveTexture(GL_TEXTURE1);
    texture2->bind();

    QMatrix4x4 transform;
    transform.translate(QVector3D(0.5f, -0.5f, 0.0f));
    transform.rotate((float)time.elapsed()/10, QVector3D(0.0f, 0.0f, 1.0f));//elapsed（）返回自start()函数开始的毫秒ms

    ourShader->use();
    ourShader->shaderProgram->setUniformValue(ourShader->shaderProgram->uniformLocation("transform"), transform);
    core->glBindVertexArray(VAO);
    core->glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);

    update();
}

vertexshadersource.vert

#version 330 core
layout (location = 0) in vec3 aPos;
layout (location = 1) in vec3 aColor;
layout (location = 2) in vec2 aTexCoord;

out vec3 ourColor;
out vec2 TexCoord;

uniform mat4 transform;

void main(){
  gl_Position = transform * vec4(aPos, 1.0f);
  ourColor = aColor;
  TexCoord = aTexCoord;
}

以下是没有改动过的函数：

fragmentshadersource.frag

#version 330 core
out vec4 FragColor;

in vec3 ourColor;
in vec2 TexCoord;

uniform sampler2D texture1;
uniform sampler2D texture2;

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

shader.h

#ifndef SHADER_H
#define SHADER_H

#include <QDebug>
#include <QOpenGLShader>
#include <QOpenGLShaderProgram>
#include <QString>

class Shader {
public:
  Shader(const QString& vertexSourcePath, const QString& fragmentSourcePath);
  ~Shader();
  QOpenGLShaderProgram shaderProgram;

  void use(){
    shaderProgram.bind();
  }


};

#endif // SHADER_H

shader.cpp

#include "shader.h"

Shader::Shader(const QString& vertexPath, const QString& fragmentPath){
    QOpenGLShader vertexShader(QOpenGLShader::Vertex);
    bool success = vertexShader.compileSourceFile(vertexPath);
    if(!success){
        qDebug() << "ERROR::SHADER::VERTEX::COMPILATION_FAILED" << endl;
        qDebug() << vertexShader.log() << endl;
    }

    QOpenGLShader fragmentShader(QOpenGLShader::Fragment);
    success  =fragmentShader.compileSourceFile(fragmentPath);
    if(!success){
        qDebug() << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED" << endl;
        qDebug() << fragmentShader.log() << endl;
    }

   shaderProgram.addShader(&vertexShader);
   shaderProgram.addShader(&fragmentShader);
   success = shaderProgram.link();
   if(!success){
        qDebug() << "ERROR::SHADER::PROGRAM::LINKING_FAILED" << endl;
        qDebug() << shaderProgram.log() << endl;
   }
}

Shader::~Shader(){
}

main.cpp

#include "widget.h"
#include <QApplication>

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

    return a.exec();
}