Drawing a triangle doesn't work on laptop Asus K53SV with Mesa using Qt 6.7.0 beta1

8Observer8

The example below should draw a red triangle but it draws nothing. It prints: OpenGL version, GLSL version, and vendor:

OpenGL Version: 3.0 Mesa 11.2.2
GLSL Version: 1.30
OpenGL Vendor: VMware, Inc.

main.cpp

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

class OpenGLWidget : public QOpenGLWidget, private QOpenGLFunctions
{
public:
    OpenGLWidget()
    {
        resize(350, 350);
        setWindowTitle("OpenGL Triangle");
    }

private:
    void initializeGL() override
    {
        initializeOpenGLFunctions();
        glClearColor(0.4f, 0.8f, 0.9f, 1.f);

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

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

        QString fragmentShaderSource =
            "#ifdef GL_ES\n"
            "precision mediump float;\n"
            "#endif\n"
            "//out vec4 fragColor;\n"
            "void main()\n"
            "{\n"
            "    gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);\n"
            "}\n";

        m_program.create();
        m_program.addShaderFromSourceCode(QOpenGLShader::ShaderTypeBit::Vertex,
                                          vertexShaderSource);
        m_program.addShaderFromSourceCode(QOpenGLShader::ShaderTypeBit::Fragment,
                                          fragmentShaderSource);
        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));
        m_program.setAttributeBuffer("aPosition", GL_FLOAT, 0, 2);
        m_program.enableAttributeArray("aPosition");
    }

    void paintGL() override
    {
        glClear(GL_COLOR_BUFFER_BIT);
        glDrawArrays(GL_TRIANGLES, 0, 4);
    }

private:
    QOpenGLShaderProgram m_program;
    QOpenGLBuffer m_vertPosBuffer;
};

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    OpenGLWidget w;
    w.show();
    return app.exec();
}

pro

QT += core gui openglwidgets widgets

win32: LIBS += -lopengl32

CONFIG = c+17

SOURCES += \
    main.cpp

I can active the integrated video card instead of Mesa by adding the AA_UseDesktopOpenGL attribute:


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

The example above prints an info about the integrated card now:


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

But a triangle is white instead of red:

To active the discrete video card I should add these lines of code to main.cpp for GeForce and Radeon:

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

It prints this info:

OpenGL Version: 4.6.0 NVIDIA 391.35
GLSL Version: 4.60 NVIDIAOpenGL
Vendor: NVIDIA Corporation

But a triangle is still white.

8Observer8

@Christian-Ehrlicher Thanks a lot! You are right! I forgot to activate (bind) the program in paintGL():

void paintGL() override
{
    m_program.bind();
    glClear(GL_COLOR_BUFFER_BIT);
    glDrawArrays(GL_TRIANGLES, 0, 4);
}

pro

QT += core gui openglwidgets widgets

win32: LIBS += -lopengl32

CONFIG += c++17

SOURCES += \
    main.cpp

main.cpp

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

class OpenGLWidget : public QOpenGLWidget, private QOpenGLFunctions
{
public:
    OpenGLWidget()
    {
        resize(350, 350);
        setWindowTitle("OpenGL Triangle");
    }

private:
    void initializeGL() override
    {
        initializeOpenGLFunctions();
        glClearColor(0.4f, 0.8f, 0.9f, 1.f);

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

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

        QString fragmentShaderSource =
            "#ifdef GL_ES\n"
            "precision mediump float;\n"
            "#endif\n"
            "//out vec4 fragColor;\n"
            "void main()\n"
            "{\n"
            "    gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);\n"
            "}\n";

        m_program.create();
        m_program.addShaderFromSourceCode(QOpenGLShader::ShaderTypeBit::Vertex,
                                          vertexShaderSource);
        m_program.addShaderFromSourceCode(QOpenGLShader::ShaderTypeBit::Fragment,
                                          fragmentShaderSource);
        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));
        m_program.setAttributeBuffer("aPosition", GL_FLOAT, 0, 2);
        m_program.enableAttributeArray("aPosition");
    }

    void paintGL() override
    {
        m_program.bind();
        glClear(GL_COLOR_BUFFER_BIT);
        glDrawArrays(GL_TRIANGLES, 0, 4);
    }

private:
    QOpenGLShaderProgram m_program;
    QOpenGLBuffer m_vertPosBuffer;
};

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    OpenGLWidget w;
    w.show();
    return app.exec();
}

8Observer8

I created a bug report about the problem above on Desktop: Drawing a triangle doesn't work on laptop Asus K53SV with Mesa using Qt 6.7.0 beta1: https://bugreports.qt.io/browse/QTBUG-120949

8Observer8

@Christian-Ehrlicher Thanks a lot! You are right! I forgot to activate (bind) the program in paintGL():

void paintGL() override
{
    m_program.bind();
    glClear(GL_COLOR_BUFFER_BIT);
    glDrawArrays(GL_TRIANGLES, 0, 4);
}

pro

QT += core gui openglwidgets widgets

win32: LIBS += -lopengl32

CONFIG += c++17

SOURCES += \
    main.cpp

main.cpp

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

class OpenGLWidget : public QOpenGLWidget, private QOpenGLFunctions
{
public:
    OpenGLWidget()
    {
        resize(350, 350);
        setWindowTitle("OpenGL Triangle");
    }

private:
    void initializeGL() override
    {
        initializeOpenGLFunctions();
        glClearColor(0.4f, 0.8f, 0.9f, 1.f);

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

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

        QString fragmentShaderSource =
            "#ifdef GL_ES\n"
            "precision mediump float;\n"
            "#endif\n"
            "//out vec4 fragColor;\n"
            "void main()\n"
            "{\n"
            "    gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);\n"
            "}\n";

        m_program.create();
        m_program.addShaderFromSourceCode(QOpenGLShader::ShaderTypeBit::Vertex,
                                          vertexShaderSource);
        m_program.addShaderFromSourceCode(QOpenGLShader::ShaderTypeBit::Fragment,
                                          fragmentShaderSource);
        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));
        m_program.setAttributeBuffer("aPosition", GL_FLOAT, 0, 2);
        m_program.enableAttributeArray("aPosition");
    }

    void paintGL() override
    {
        m_program.bind();
        glClear(GL_COLOR_BUFFER_BIT);
        glDrawArrays(GL_TRIANGLES, 0, 4);
    }

private:
    QOpenGLShaderProgram m_program;
    QOpenGLBuffer m_vertPosBuffer;
};

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    OpenGLWidget w;
    w.show();
    return app.exec();
}