我的qtopengl小部件没有出现？

Question

main.cpp

#include "QtGuiApplication4.h"
#include <QtWidgets/QApplication>
#include "megui.h"

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

    return a.exec();
}

qtguiapplication4.h

#pragma once

#include <QtWidgets/QMainWindow>
#include "ui_QtGuiApplication4.h"

class QtGuiApplication4 : public QMainWindow
{
    Q_OBJECT

public:
    QtGuiApplication4(QWidget *parent = Q_NULLPTR);

private:
    Ui::QtGuiApplication4Class ui;
};

qtguiapplication4.cpp

#include "QtGuiApplication4.h"

QtGuiApplication4::QtGuiApplication4(QWidget *parent)
    : QMainWindow(parent)
{
    ui.setupUi(this);
}

megui.h

#pragma once
#include "QOpenGLWidget"
#include "QOpenGLBuffer"
#include "QOpenGLFunctions"
#include "QOpenGLShaderProgram"
#include <iostream>
class megui:public QOpenGLWidget, protected QOpenGLFunctions
{
public:
    QOpenGLFunctions glfunctions;
    QOpenGLShaderProgram program;

    void initializeGL();
    void paintGL();

    megui();
    ~megui();
};

megui.cpp

#include "megui.h"

void megui::initializeGL()
{
    makeCurrent();
    float vertexpositions[] = {
        0.5f,0.5f,
        0.0f,-0.5f,
        0.5f,-0.5f
    };
    QOpenGLBuffer buffer1(QOpenGLBuffer::VertexBuffer);
    buffer1.create();
    buffer1.setUsagePattern(QOpenGLBuffer::StaticDraw);
    buffer1.allocate(vertexpositions, sizeof(vertexpositions));
    buffer1.bind();
    glfunctions.initializeOpenGLFunctions();
    glfunctions.glEnableVertexAttribArray(0);
    glfunctions.glVertexAttribPointer(0, 3, GL_FLOAT, false, 0, 0);

    program.addShaderFromSourceFile(QOpenGLShader::Vertex, "C:/open gl testimg/opengl testing/opengl testing/vertex.glsl");
    program.addShaderFromSourceFile(QOpenGLShader::Fragment, "C:/open gl testimg/opengl testing/opengl testing/fragmentshader.glsl");
    program.link();
}

void megui::paintGL()
{
    makeCurrent();

    glfunctions.initializeOpenGLFunctions();

    program.bind();
    glfunctions.glDrawArrays(GL_TRIANGLES, 0, 3);   
}

megui::megui()
{
}

megui::~megui()
{
}

碎片着色器

#version 430

out vec4 inalcolors;

void main() {

    inalcolors =vec4( 1.0f, 0.0f, 0.0f,1.0) ;
}

顶点着色器

#version 430 

layout(location = 0) in vec4 positions;

void main() {

    gl_Position =positions; 
}

小部件屏幕没有显示出来，但是当我删除glDrawArrays调用时，它就会显示出来。我怀疑opengl代码中有什么问题导致了这个问题。我按照youtube的教程，他和我的代码都是一样的，我希望我使用的是qt opengl包装类，而不是glew library.what。

Answer 1

QOpenGLBuffer buffer1是megui::initializeGL()方法中的局部变量。Qt OpenGL对象使用资源获取是初始化(RAII)技术。这意味着在函数的末尾，buffer1被破坏，缓冲区消失，无效。

此外，QOpenGLBuffer对象必须在之前绑定(bind()) ，然后才能分配(allocate())。请参阅QOpenGLBuffer::allocate的文档。

顺便说一句，你的顶点坐标由两个组件组成(x，y)，而不是3。

在类QOpenGLBuffer中创建megui成员

class megui:public QOpenGLWidget, protected QOpenGLFunctions
{
public:
    QOpenGLFunctions glfunctions;
    QOpenGLShaderProgram program;

    QOpenGLBuffer buffer1;

    .....
}

​

megui::megui()
    : buffer1(QOpenGLBuffer::VertexBuffer)
{}

在分配缓冲区之前绑定它：

void megui::initializeGL()
{
    .....

    buffer1.create();
    buffer1.setUsagePattern(QOpenGLBuffer::StaticDraw);

    buffer1.bind(); // <-------- bind before allocate
    buffer1.allocate(vertexpositions, sizeof(vertexpositions));


    float vertexpositions[] = {
        0.5f,0.5f,
        0.0f,-0.5f,
        0.5f,-0.5f
    };

    glfunctions.glEnableVertexAttribArray(0);

    glfunctions.glVertexAttribPointer(
        0, 2,       // <-------- 2 instead of 3
        GL_FLOAT, false, 0, 0);

    buffer1.release();

    .....
}