基于Qt的OpenGL學習（2）—— 著色器

簡介

要學習OpenGL的話，強烈安利這個教程JoeyDeVries的learnopengl，這里是中文翻譯好的版本。教程中使用OpenGL是通過GLFW這個庫，而在Qt中對OpenGL封裝得很好，并且和GUI以及IO相關的處理Qt更便捷，學習起來更輕松。這里就對每篇教程，在Qt在分別直接使用OpenGL的函數和Qt封裝好的類以作對比。
教程中使用的OpenGL版本為3.3，在Qt中需要使用此版本的OpenGL只需要繼承類QOpenGLFunctions_3_3_Core即可。如果為了在不同設備上都能用OpenGL的話，Qt提供了類QOpenGLFunctions，這個類包含了大部分公共的函數，可能會有個別函數不能用。

對比說明

教程地址

原教程地址，相關知識可以點擊鏈接學習。
我的工程地址，準備后期每篇教程一個commit，可以切換著看，查看本篇代碼 git checkout v1.2，喜歡就點個Star吧~

不同點 (僅列出新增)

  1. 我的代碼實現的是原教程中練習2的三角形沿著X軸水平移動
  2. 原教程是一個while循環(huán)不停重繪，Qt中的paintGL則是在需要時才重繪，因此采用QTimer定時器觸發(fā)重繪刷新。

運行結果

運行結果

使用OpenGL函數版

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;
    float m_uniformValue = 0.0f;
};

#endif // COREFUNCTIONWIDGET_H

CoreFunctionWidget.cpp

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

static GLuint VBO, VAO, EBO;

CoreFunctionWidget::CoreFunctionWidget(QWidget *parent) : QOpenGLWidget(parent)
{
    m_pTimer = new QTimer(this);
    m_pTimer->setInterval(200);

    connect(m_pTimer, &QTimer::timeout, this, [=]{
        m_uniformValue += 0.1f;

        if (m_uniformValue > 1.5f) {
            m_uniformValue = -1.5f;
        }

        update();
    });

    m_pTimer->start();
}

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

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

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

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

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

    //VAO，VBO數據部分
    float vertices[] = {
        // positions         // colors
        0.5f, -0.5f, 0.0f,  1.0f, 0.0f, 0.0f,  // bottom right
        -0.5f, -0.5f, 0.0f,  0.0f, 1.0f, 0.0f,  // bottom left
        0.0f,  0.5f, 0.0f,  0.0f, 0.0f, 1.0f   // top
    };
//    unsigned int indices[] = {  // note that we start from 0!
//        0, 1, 3,  // first Triangle
//        1, 2, 3   // second Triangle
//    };

    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);
//    glGenBuffers(1, &EBO);
    // 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);  //頂點數據復制到緩沖

//    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
//    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);

    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(GLfloat), (void*)0);
    glEnableVertexAttribArray(0);
    glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(GLfloat), (GLvoid*)(3*sizeof(GLfloat)));
    glEnableVertexAttribArray(1);

    glBindBuffer(GL_ARRAY_BUFFER, 0);//取消VBO的綁定, glVertexAttribPointer已經把頂點屬性關聯到頂點緩沖對象了

//    remember: do NOT unbind the EBO while a VAO is active as the bound element buffer object IS stored in the VAO; keep the EBO bound.
//    glBindBuffer(GL_ELEMENT_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);   //取消VAO綁定

    //線框模式，QOpenGLExtraFunctions沒這函數, 3_3_Core有
//    glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
}

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

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

    shaderProgram.bind();
    {
        int xOffsetLocation = shaderProgram.uniformLocation("xOffset");
        glUniform1f(xOffsetLocation, m_uniformValue);

        // 繪制三角形
        glBindVertexArray(VAO);
        glDrawArrays(GL_TRIANGLES, 0, 3);

//        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, 6);
//        glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
    }
    shaderProgram.release();
}

使用Qt相關函數版

QtFunctionWidget.h

#ifndef QTFUNCTIONWIDGET_H
#define QTFUNCTIONWIDGET_H

#include <QOpenGLWidget>


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

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, ebo;
    QOpenGLVertexArrayObject vao;

    QTimer* m_pTimer = nullptr;
    float m_uniformValue = 0.0f;
};

#endif // QTFUNCTIONWIDGET_H

QtFunctionWidget.cpp

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

QtFunctionWidget::QtFunctionWidget(QWidget *parent) : QOpenGLWidget (parent),
    vbo(QOpenGLBuffer::VertexBuffer),
    ebo(QOpenGLBuffer::IndexBuffer)
{
    m_pTimer = new QTimer(this);
    m_pTimer->setInterval(200);

    connect(m_pTimer, &QTimer::timeout, this, [=]{
        m_uniformValue += 0.1f;

        if (m_uniformValue > 1.5f) {
            m_uniformValue = -1.5f;
        }

        update();
    });

    m_pTimer->start();
}

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

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

    doneCurrent();
}

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

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

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

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

    //VAO，VBO數據部分
    GLfloat vertices[] = {
        // positions         // colors
        0.5f, -0.5f, 0.0f,  1.0f, 0.0f, 0.0f,  // bottom right
        -0.5f, -0.5f, 0.0f,  0.0f, 1.0f, 0.0f,  // bottom left
        0.0f,  0.5f, 0.0f,  0.0f, 0.0f, 1.0f   // top
    };
//    unsigned int indices[] = {  // note that we start from 0!
//        0, 1, 3,  // first Triangle
//        1, 2, 3   // second Triangle
//    };

    QOpenGLVertexArrayObject::Binder vaoBind(&vao);

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

//    ebo.create();
//    ebo.bind();
//    ebo.allocate(indices, sizeof(indices));

    int attr = -1;
    attr = shaderProgram.attributeLocation("aPos");
    shaderProgram.setAttributeBuffer(attr, GL_FLOAT, 0, 3, sizeof(GLfloat) * 6);
    shaderProgram.enableAttributeArray(attr);

    attr = shaderProgram.attributeLocation("aColor");
    shaderProgram.setAttributeBuffer(attr, GL_FLOAT, sizeof(GLfloat) * 3, 3, sizeof(GLfloat) * 6);
    shaderProgram.enableAttributeArray(attr);

    vbo.release();
//    remember: do NOT unbind the EBO while a VAO is active as the bound element buffer object IS stored in the VAO; keep the EBO bound.
//    ebo.release();

}

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

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

    shaderProgram.bind();
    {
        shaderProgram.setUniformValue("xOffset", m_uniformValue);

        QOpenGLVertexArrayObject::Binder vaoBind(&vao);
        glDrawArrays(GL_TRIANGLES, 0, 3);

//        glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
    }
    shaderProgram.release();
}

GLSL

colortriangle.vert

#version 330 core
layout (location = 0) in vec3 aPos;
layout (location = 1) in vec3 aColor;
 
out vec3 ourColor;
uniform float xOffset;
 
void main(){
  gl_Position = vec4(aPos.x + xOffset, aPos.y, aPos.z, 1.0);
  ourColor = aColor;
}

colortriangle.frag

#version 330 core
out vec4 FragColor;
in vec3 ourColor;
 
void main(void)
{
    FragColor = vec4(ourColor, 1.0f);
}

main.cpp

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

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

//    MainWindow w;
    QtFunctionWidget w1;
    CoreFunctionWidget w2;

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

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

    return a.exec();
}
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