Qt's OpenGL vertex binding funcs problem

[8Observer8]

My laptop has two video cards: integrated on CPU and discrete GeForce. Qt uses the first one by default:

qDebug() << "OpenGL version:" << (const char*) glGetString(GL_VERSION);
qDebug() << "GLSL version: " << (const char*) glGetString(GL_SHADING_LANGUAGE_VERSION);
qDebug() << "Vendor: " << (const char*) glGetString(GL_VENDOR);

Output:

OpenGL version: 3.1.0 - Build 9.17.10.4459
GLSL version:  1.40 - Intel Build 9.17.10.4459
Vendor:  Intel

I am not expert in Qt but it is very interesting that the QOpenGLFunctions_3_3_Core.h header file is not available for me. I see it here:

But I don't see it here:

Even QOpenGLFunctions_3_1.h is not in the list.

[Bondrusiek]

Hmm, you can try run it and see result. Maybe compilation sees a OpenGL version and blocks some header files:

#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QSurfaceFormat fmt;
    fmt.setDepthBufferSize(24);

    // Request OpenGL 3.3 core or OpenGL ES 3.0.
    if (QOpenGLContext::openGLModuleType() == QOpenGLContext::LibGL) {
        qDebug("Requesting 3.3 core context");
        fmt.setVersion(3, 3);
        fmt.setProfile(QSurfaceFormat::CoreProfile);
    } else {
        qDebug("Requesting 3.0 context");
        fmt.setVersion(3, 0);
    }

    QSurfaceFormat::setDefaultFormat(fmt);

    return a.exec();
}

[8Observer8]

Output:

Requesting 3.3 core context
OpenGL version: 3.1.0 - Build 9.17.10.4459
GLSL version:  1.40 - Intel Build 9.17.10.4459
Vendor:  Intel

main.cpp

#include <QtGui/QOpenGLContext>
#include <QtGui/QOpenGLFunctions>
#include <QtGui/QSurfaceFormat>
#include <QtWidgets/QApplication>
#include <QtOpenGL/QOpenGLWindow>

class OpenGLWindow : public QOpenGLWindow, private QOpenGLFunctions
{
    void initializeGL() override
    {
        initializeOpenGLFunctions();

        qDebug() << "OpenGL version:" << (const char*) glGetString(GL_VERSION);
        qDebug() << "GLSL version: " << (const char*) glGetString(GL_SHADING_LANGUAGE_VERSION);
        qDebug() << "Vendor: " << (const char*) glGetString(GL_VENDOR);
    }
};

int main(int argc, char *argv[])
{
    QApplication::setAttribute(Qt::ApplicationAttribute::AA_UseDesktopOpenGL);
    QApplication app(argc, argv);
    QSurfaceFormat fmt;
    fmt.setDepthBufferSize(24);

    // Request OpenGL 3.3 core or OpenGL ES 3.0.
    if (QOpenGLContext::openGLModuleType() == QOpenGLContext::LibGL)
    {
        qDebug("Requesting 3.3 core context");
        fmt.setVersion(3, 3);
        fmt.setProfile(QSurfaceFormat::CoreProfile);
    }
    else
    {
        qDebug("Requesting 3.0 context");
        fmt.setVersion(3, 0);
    }

    OpenGLWindow w;
    w.setFormat(fmt);
    w.show();
    return app.exec();
}

[8Observer8]

I can activate the discrete GeForce (or Radeon) card by adding this code:

#ifdef _WIN32
#include <windows.h>
extern "C" __declspec(dllexport) DWORD NvOptimusEnablement = 0x00000001;
extern "C" __declspec(dllexport) DWORD AmdPowerXpressRequestHighPerformance = 0x00000001;
#endif

Output:

Requesting 3.3 core context
OpenGL version: 3.3.0 NVIDIA 391.35
GLSL version:  3.30 NVIDIA via Cg compiler
Vendor:  NVIDIA Corporation

main.cpp

#ifdef _WIN32
#include <windows.h>
extern "C" __declspec(dllexport) DWORD NvOptimusEnablement = 0x00000001;
extern "C" __declspec(dllexport) DWORD AmdPowerXpressRequestHighPerformance = 0x00000001;
#endif

#include <QtGui/QOpenGLContext>
#include <QtGui/QOpenGLFunctions>
#include <QtGui/QSurfaceFormat>
#include <QtWidgets/QApplication>
#include <QtOpenGL/QOpenGLWindow>

class OpenGLWindow : public QOpenGLWindow, private QOpenGLFunctions
{
    void initializeGL() override
    {
        initializeOpenGLFunctions();

        qDebug() << "OpenGL version:" << (const char*) glGetString(GL_VERSION);
        qDebug() << "GLSL version: " << (const char*) glGetString(GL_SHADING_LANGUAGE_VERSION);
        qDebug() << "Vendor: " << (const char*) glGetString(GL_VENDOR);
    }
};

int main(int argc, char *argv[])
{
    QApplication::setAttribute(Qt::ApplicationAttribute::AA_UseDesktopOpenGL);
    QApplication app(argc, argv);
    QSurfaceFormat fmt;
    fmt.setDepthBufferSize(24);

    // Request OpenGL 3.3 core or OpenGL ES 3.0.
    if (QOpenGLContext::openGLModuleType() == QOpenGLContext::LibGL)
    {
        qDebug("Requesting 3.3 core context");
        fmt.setVersion(3, 3);
        fmt.setProfile(QSurfaceFormat::CoreProfile);
    }
    else
    {
        qDebug("Requesting 3.0 context");
        fmt.setVersion(3, 0);
    }

    OpenGLWindow w;
    w.setFormat(fmt);
    w.show();
    return app.exec();
}

[Bondrusiek]

So you have a card that supports OpenGL 3.3. It's strange that Qt doesn't see this header files. If I had anything to suggest, you can update Qt via MaintenanceTool and update the graphics card drivers.

[8Observer8]

@Bondrusiek said in Qt's OpenGL vertex binding funcs problem:

update the graphics card drivers

I have the latest: OpenGL 4.6 for GeForce and OpenGL 3.1.0 for Intel. I cannot update OpenGL for Intel because 3.1 is maximum for my CPU.

@Bondrusiek said in Qt's OpenGL vertex binding funcs problem:

It's strange that Qt doesn't see this header files.

I see them now:

[8Observer8]

I don't understand why but there is no the QOpenGLFunctions_3_3_Core: No such file or directory error in your first example. It crashed: debug\opengl33-test.exe crashed. But it is crashed because I have a laptop and Qt runs with the integrated video card with OpenGL 3.1. I have added these lines to the main.cpp:

#ifdef _WIN32
#include <windows.h>
extern "C" __declspec(dllexport) DWORD NvOptimusEnablement = 0x00000001;
extern "C" __declspec(dllexport) DWORD AmdPowerXpressRequestHighPerformance = 0x00000001;
#endif

and your first example works now. I the the red triangle. But it prints the maximum version of OpenGL 4.6 on the discrete video card because setVersion(3 , 3) was not called:

OpenGL version: 4.6.0 NVIDIA 391.35
GLSL version:  4.60 NVIDIA
Vendor:  NVIDIA Corporation

[8Observer8]

Sorry. I have forgot to add setVersion(3, 3) to the main.cpp file. Now your first example prints correct version of OpenGL:

Requesting 3.3 core context
OpenGL version: 3.3.0 NVIDIA 391.35
GLSL version:  3.30 NVIDIA via Cg compiler
Vendor:  NVIDIA Corporation

But I don't see a red triangle. I can fix it only by comment the QSurfaceFormat code with setting setVersion and setProfile but it uses OpenGL 4.6 now:

main.cpp

#ifdef _WIN32
#include <windows.h>
extern "C" __declspec(dllexport) DWORD NvOptimusEnablement = 0x00000001;
extern "C" __declspec(dllexport) DWORD AmdPowerXpressRequestHighPerformance = 0x00000001;
#endif

#include "glwidget.h"

#include <QtGui/QSurfaceFormat>
#include <QtWidgets/QApplication>

int main(int argc, char *argv[])
{
    QApplication::setAttribute(Qt::ApplicationAttribute::AA_UseDesktopOpenGL);
    QApplication a(argc, argv);

    QSurfaceFormat fmt;
    fmt.setDepthBufferSize(24);

    // // Request OpenGL 3.3 core or OpenGL ES 3.0.
    // if (QOpenGLContext::openGLModuleType() == QOpenGLContext::LibGL) {
    //     qDebug("Requesting 3.3 core context");
    //     fmt.setVersion(3, 3);
    //     fmt.setProfile(QSurfaceFormat::CoreProfile);
    // } else {
    //     qDebug("Requesting 3.0 context");
    //     fmt.setVersion(3, 0);
    // }

    QSurfaceFormat::setDefaultFormat(fmt);

    MyGLWidget w;
    w.show();
    return a.exec();
}

[Bondrusiek]

Thanks for checking. As far as I know, in the case of shaders, you can also indicate what version of OpenGL you want to use.
#version 330 core
This means that you want to use 3.3 version of OpenGL. #version 460 core means set OpenGL to 4.6.

Perhaps the most important thing is that the second example does not render the triangle correctly for you either. Just like in my case, so I guess we can talk about a bug here.

[8Observer8]

I believe there is no need to spend time on OpenGL 3.3 Core, especially if you have just started learning the basics of OpenGL. You can defer learning OpenGL 3.3 Core until the next iteration. Take OpenGL ES 2.0. It's much smaller. It has all the basic things you need now. It works on iOS, Android and web browser. In the near future, focus on OpenGL ES 2.0 and make demos and small games on it. It will serve you for several years, and maybe a lifetime.

My simple triangle example is written using OpenGL ES 2.0. It is compiled to Desktop, Mobile, and Web from one code base.

• Demo in the browser using QOpenGLWindow
• Demo in the browser using QOpenGLWidget

main.cpp

#include <QtGui/QOpenGLFunctions>
#include <QtOpenGL/QOpenGLBuffer>
#include <QtOpenGL/QOpenGLShader>
#include <QtOpenGL/QOpenGLShaderProgram>
#include <QtOpenGLWidgets/QOpenGLWidget>
#include <QtWidgets/QApplication>

class OpenGLWindow : public QOpenGLWidget, private QOpenGLFunctions
{
public:
    OpenGLWindow()
    {
        setWindowTitle("OpenGL ES 2.0, Qt6, C++");
        resize(350, 350);
    }

    void initializeGL() override
    {
        initializeOpenGLFunctions();
        glClearColor(48.f / 255.f, 56.f / 255.f, 65.f / 255.f, 1.f);

        QString vertShaderSrc =
            "attribute vec2 aPosition;\n"
            "void main()\n"
            "{\n"
            "    gl_Position = vec4(aPosition, 0.0, 1.0);\n"
            "}\n";

        QString fragShaderSrc =
            "#ifdef GL_ES\n"
            "precision mediump float;\n"
            "#endif\n"
            "void main()\n"
            "{\n"
            "    gl_FragColor = vec4(0.2, 0.7, 0.3, 1.0);\n"
            "}\n";

        m_program.create();
        m_program.addShaderFromSourceCode(QOpenGLShader::ShaderTypeBit::Vertex, vertShaderSrc);
        m_program.addShaderFromSourceCode(QOpenGLShader::ShaderTypeBit::Fragment, fragShaderSrc);
        m_program.link();
        m_program.bind();

        float vertPositions[] = {
            -0.5f, -0.5f,
            0.5f, -0.5f,
            0.f, 0.5f
        };
        m_vertPosBuffer.create();
        m_vertPosBuffer.bind();
        m_vertPosBuffer.allocate(vertPositions, sizeof(vertPositions));
    }

    void paintGL() override
    {
        glClear(GL_COLOR_BUFFER_BIT);
        m_program.bind();
        m_vertPosBuffer.bind();
        m_program.setAttributeBuffer("aPosition", GL_FLOAT, 0, 2);
        m_program.enableAttributeArray("aPosition");
        glDrawArrays(GL_TRIANGLES, 0, 3);
    }

private:
    QOpenGLShaderProgram m_program;
    QOpenGLBuffer m_vertPosBuffer;
};

int main(int argc, char *argv[])
{
    QApplication::setAttribute(Qt::ApplicationAttribute::AA_UseDesktopOpenGL);
    QApplication app(argc, argv);
    OpenGLWindow w;
    w.show();
    return app.exec();
}

QT += core gui openglwidgets

win32: LIBS += -lopengl32

CONFIG += c++17

SOURCES += \
    main.cpp

[8Observer8]

I have created the bug report: https://bugreports.qt.io/browse/QTBUG-126389

I have tested with QOpenGLWindow. The result is the same.

[8Observer8]

My bug report was closed with the comment: You need a VAO to use a Core profile.

I have added solution examples to the bug report:

• solution-qopenglwidget.zip
• solution-qopenglwindow.zip

Steps to solve the problem:

• Add #include <QtOpenGL/QOpenGLVertexArrayObject> inside of the glwidget.h
• Create the QOpenGLVertexArrayObject vao; member inside of the MyGLWidget class
• Create and bind vao inside of the initializeGL method:

void MyGLWidget::initializeGL()
{
    initializeOpenGLFunctions();
    vao.create();
    vao.bind();

• Delete a binding of the vbo inside of the paintGL()
• Add a binding of the vao inside of the paintGL()
• Move attributeLocation, enableAttributeArray and setAttributeBuffer inside of the initializeGL method:
• I don't think that you should release the shader program inside of the paintGL() method
• Release vao inside of the paintGL() method
• I think you don't need to call disableAttributeArray inside of the paintGL() method

So, VAO allows to bind VBO and call enableAttributeArray and setAttributeBuffer only one time. You can bind VAO only inside of the paintGL() method. Now the program works:

pro

QT += core gui openglwidgets opengl

win32: LIBS += -lopengl32

CONFIG += c++17

SOURCES += \
    main.cpp \
    glwidget.cpp

HEADERS += \
    glwidget.h

glwidget.h

#ifndef GLWIDGET_H
#define GLWIDGET_H

#include <QOpenGLWidget>
#include <QOpenGLFunctions_3_3_Core>
#include <QOpenGLBuffer>
#include <QOpenGLShaderProgram>
#include <QtOpenGL/QOpenGLVertexArrayObject>

class MyGLWidget : public QOpenGLWidget, protected QOpenGLFunctions_3_3_Core
{
    Q_OBJECT

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

protected:
    void initializeGL() override;
    void resizeGL(int w, int h) override;
    void paintGL() override;

private:
    QOpenGLBuffer vbo;
    QOpenGLVertexArrayObject vao;
    QOpenGLShaderProgram *shaderProgram;
};

#endif // GLWIDGET_H

glwidget.cpp

#include "glwidget.h"

MyGLWidget::MyGLWidget(QWidget *parent)
    : QOpenGLWidget(parent), vbo(QOpenGLBuffer::VertexBuffer)
{
    setWindowTitle("Trianlge, OpenGL 3.3 Core");
    resize(500, 500);
}

MyGLWidget::~MyGLWidget()
{
    makeCurrent();
    vao.destroy();
    vbo.destroy();
    delete shaderProgram;
    doneCurrent();
}

void MyGLWidget::initializeGL()
{
    initializeOpenGLFunctions();

    qDebug() << "OpenGL version:" << (const char*) glGetString(GL_VERSION);
    qDebug() << "GLSL version: " << (const char*) glGetString(GL_SHADING_LANGUAGE_VERSION);
    qDebug() << "Vendor: " << (const char*) glGetString(GL_VENDOR);

    shaderProgram = new QOpenGLShaderProgram();
    shaderProgram->addShaderFromSourceCode(QOpenGLShader::Vertex,
        "#version 330 core\n"
        "layout(location = 0) in vec3 position;\n"
        "void main()\n"
        "{\n"
        "    gl_Position = vec4(position, 1.0);\n"
        "}\n"
        );
    shaderProgram->addShaderFromSourceCode(QOpenGLShader::Fragment,
        "#version 330 core\n"
        "out vec4 fragColor;\n"
        "void main()\n"
        "{\n"
        "    fragColor = vec4(1.0, 0.0, 0.0, 1.0);\n"
        "}\n"
        );
    shaderProgram->link();
    shaderProgram->bind();

    vao.create();
    vao.bind();
    vbo.create();
    vbo.bind();

    GLfloat vertices[] = {
        0.0f,  0.5f, 0.0f, // Top vertex
        -0.5f, -0.5f, 0.0f, // Bottom left vertex
        0.5f, -0.5f, 0.0f  // Bottom right vertex
    };

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

    int posLocation = shaderProgram->attributeLocation("position");
    shaderProgram->enableAttributeArray(posLocation);
    shaderProgram->setAttributeBuffer(posLocation, GL_FLOAT, 0, 3);

    vao.release();
}

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

void MyGLWidget::paintGL()
{
    glClear(GL_COLOR_BUFFER_BIT);

    shaderProgram->bind();
    vao.bind();

    glDrawArrays(GL_TRIANGLES, 0, 3);

    vao.release();
}

main.cpp

#ifdef _WIN32
#include <windows.h>
extern "C" __declspec(dllexport) DWORD NvOptimusEnablement = 0x00000001;
extern "C" __declspec(dllexport) DWORD AmdPowerXpressRequestHighPerformance = 0x00000001;
#endif

#include "glwidget.h"

#include <QtGui/QSurfaceFormat>
#include <QtWidgets/QApplication>

int main(int argc, char *argv[])
{
    QApplication::setAttribute(Qt::ApplicationAttribute::AA_UseDesktopOpenGL);
    QApplication a(argc, argv);

    QSurfaceFormat fmt;
    fmt.setDepthBufferSize(24);

    // Request OpenGL 3.3 core or OpenGL ES 3.0.
    if (QOpenGLContext::openGLModuleType() == QOpenGLContext::LibGL) {
        qDebug("Requesting 3.3 core context");
        fmt.setVersion(3, 3);
        fmt.setProfile(QSurfaceFormat::CoreProfile);
    } else {
        qDebug("Requesting 3.0 context");
        fmt.setVersion(3, 0);
    }

    QSurfaceFormat::setDefaultFormat(fmt);

    MyGLWidget w;
    w.show();
    return a.exec();
}

[8Observer8]

I think it is a solution. You can mark it as a solution: