Small examples for game development in Qt, OpenGL, Box2D, Bullet Physics, and OpenAL

[8Observer8]

Moving a disk by mouse and touching

WebAssembly demo on free Netlify hosting

move-disk-by-mouse-and-touching-opengles2-qt6-cpp.pro

QT += core gui openglwidgets

CONFIG += c++17

SOURCES += \
    main.cpp

main.cpp

#include <QtMath>
#include <QtGui/QMatrix4x4>
#include <QtGui/QMouseEvent>
#include <QtGui/QOpenGLFunctions>
#include <QtGui/QSurfaceFormat>
#include <QtGui/QVector3D>
#include <QtOpenGL/QOpenGLBuffer>
#include <QtOpenGL/QOpenGLShader>
#include <QtOpenGL/QOpenGLShaderProgram>
#include <QtOpenGL/QOpenGLWindow>
#include <QtWidgets/QApplication>

class OpenGLWindow : public QOpenGLWindow, private QOpenGLFunctions
{
public:
    OpenGLWindow()
    {
        setTitle("OpenGL ES 2.0, Qt6, C++");
        resize(380, 380);

        QSurfaceFormat surfaceFormat;
        surfaceFormat.setDepthBufferSize(24);
        surfaceFormat.setSamples(4);
        setFormat(surfaceFormat);
    }

    void initializeGL() override
    {
        initializeOpenGLFunctions();
        glClearColor(0.04f, 0.62f, 0.48f, 1.f);

        QString vertShaderSrc =
            "attribute vec2 aPosition;\n"
            "uniform mat4 uMvpMatrix;"
            "void main()\n"
            "{\n"
            "    gl_Position = uMvpMatrix * vec4(aPosition, 0.0, 1.0);\n"
            "}\n";

        QString fragShaderSrc =
            "#ifdef GL_ES\n"
            "precision mediump float;\n"
            "#endif\n"
            "uniform vec3 uColor;\n"
            "void main()\n"
            "{\n"
            "    gl_FragColor = vec4(uColor, 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[m_amountOfDiskVertices * 2 + 8]; // Disk + Square
        float radius = 0.5f;
        float angle = 0.f;

        int index = 0;
        // Disk center
        vertPositions[index++] = 0.f;
        vertPositions[index++] = 0.f;

        // Disk
        for (int i = 0; i < m_amountOfDiskVertices - 1; i++)
        {
            float radians = qDegreesToRadians(angle);
            float x = radius * qCos(radians);
            float y = radius * qSin(radians);
            vertPositions[index++] = x;
            vertPositions[index++] = y;
            angle += m_angleStep;
        }
        // Square
        vertPositions[index++] = -0.5f;
        vertPositions[index++] = -0.5f;
        vertPositions[index++] = 0.5f;
        vertPositions[index++] = -0.5f;
        vertPositions[index++] = -0.5f;
        vertPositions[index++] = 0.5f;
        vertPositions[index++] = 0.5f;
        vertPositions[index++] = 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");

        m_uColorLocation = m_program.uniformLocation("uColor");
        m_uMvpMatrixLocation = m_program.uniformLocation("uMvpMatrix");
        m_viewMatrix.lookAt(QVector3D(0, 0, 1), QVector3D(0, 0, 0), QVector3D(0, 1, 0));
    }

    void resizeGL(int w, int h) override
    {
        int deviceW = w * devicePixelRatio();
        int deviceH = h * devicePixelRatio();
        float deviceAspect = deviceH / (float) deviceW;

        if (deviceAspect > m_worldAspect)
        {
            m_viewportWidth = deviceW;
            m_viewportHeight = (int) deviceW * m_worldAspect;
            m_viewportX = 0;
            m_viewportY = (int) (deviceH - m_viewportHeight) / 2.f;
        }
        else
        {
            m_viewportWidth = (int) deviceH / m_worldAspect;
            m_viewportHeight = deviceH;
            m_viewportX = (int) (deviceW - m_viewportWidth) / 2.f;
            m_viewportY = 0;
        }
        m_projMatrix.setToIdentity();
        m_projMatrix.ortho(0.f, m_worldWidth, 0.f, m_worldHeight, 1.f, -1.f);
        m_projViewMatrix = m_projMatrix * m_viewMatrix;
    }

    void paintGL() override
    {
        glClear(GL_COLOR_BUFFER_BIT);
        glClearColor(0.2, 0.2, 0.2, 1);
        glClear(GL_COLOR_BUFFER_BIT);
        glViewport(m_viewportX, m_viewportY, m_viewportWidth, m_viewportHeight);
        glScissor(m_viewportX, m_viewportY, m_viewportWidth, m_viewportHeight);
        glClearColor(0.04, 0.62, 0.48, 1);
        glEnable(GL_SCISSOR_TEST);
        glClear(GL_COLOR_BUFFER_BIT);
        glDisable(GL_SCISSOR_TEST);

        // Square
        drawRectangle(100, 50, 50, 50, 0, QVector3D(0.3, 0.07, 0.5));
        // Disk
        drawDisk(m_diskPosX, m_diskPosY, 50, QVector3D(0.8, 0.8, 0.5));
        // Left border
        drawRectangle(5, 50, 5, 85, 0, QVector3D(0.62, 0.04, 0.18));
        // Right border
        drawRectangle(195, 50, 5, 85, 0, QVector3D(0.62, 0.04, 0.18));
        // Top border
        drawRectangle(100, 95, 185, 5, 0, QVector3D(0.62, 0.04, 0.18));
        // Bottom border
        drawRectangle(100, 5, 185, 5, 0, QVector3D(0.62, 0.04, 0.18));
    }

    void drawDisk(float x, float y, float diameter, const QVector3D& color)
    {
        m_modelMatrix.setToIdentity();
        m_modelMatrix.translate(QVector3D(x, y, 0));
        m_modelMatrix.scale(QVector3D(diameter, diameter, 1));
        m_mvpMatrix = m_projViewMatrix * m_modelMatrix;
        m_program.setUniformValue(m_uMvpMatrixLocation, m_mvpMatrix);
        m_program.setUniformValue(m_uColorLocation, color);
        glDrawArrays(GL_TRIANGLE_FAN, 0, m_amountOfDiskVertices);
    }

    void drawRectangle(float x, float y, float w, float h,
        float angle, const QVector3D& color)
    {
        m_modelMatrix.setToIdentity();
        m_modelMatrix.translate(QVector3D(x, y, 0));
        m_modelMatrix.rotate(angle, QVector3D(0, 0, 1));
        m_modelMatrix.scale(QVector3D(w, h, 1));
        m_mvpMatrix = m_projViewMatrix * m_modelMatrix;
        m_program.setUniformValue(m_uMvpMatrixLocation, m_mvpMatrix);
        m_program.setUniformValue(m_uColorLocation, color);
        glDrawArrays(GL_TRIANGLE_STRIP, m_amountOfDiskVertices, 4);
    }

    void mousePressEvent(QMouseEvent *event) override
    {
        switch (event->button()) {
            case Qt::MouseButton::LeftButton:
            {
                m_mouseHolding = true;
                int x = event->pos().x() * devicePixelRatio();
                int y = (height() - event->pos().y() - 1) * devicePixelRatio();
                if ((m_viewportX <= x && x < (m_viewportX + m_viewportWidth)) &&
                    (m_viewportY <= y && y < (m_viewportY + m_viewportHeight)))
                {
                    float normalizedX = (x - m_viewportX) / (float) m_viewportWidth;
                    float normalizedY = (y - m_viewportY) / (float) m_viewportHeight;
                    m_diskPosX = m_worldWidth * normalizedX;
                    m_diskPosY = m_worldHeight * normalizedY;
                }
                update();
                break;
            }
            default:
                break;
        }
    }

    void mouseMoveEvent(QMouseEvent *event) override
    {
        if (!m_mouseHolding)
            return;

        int x = event->pos().x() * devicePixelRatio();
        int y = (height() - event->pos().y() - 1) * devicePixelRatio();
        if ((m_viewportX <= x && x < (m_viewportX + m_viewportWidth)) &&
            (m_viewportY <= y && y < (m_viewportY + m_viewportHeight)))
        {
            float normalizedX = (x - m_viewportX) / (float) m_viewportWidth;
            float normalizedY = (y - m_viewportY) / (float) m_viewportHeight;
            m_diskPosX = m_worldWidth * normalizedX;
            m_diskPosY = m_worldHeight * normalizedY;
        }
        update();
    }

    void mouseReleaseEvent(QMouseEvent *event) override
    {
        switch (event->button()) {
            case Qt::MouseButton::LeftButton:
            {
                m_mouseHolding = false;
                break;
            }
            default:
                break;
        }
    }

private:
    QOpenGLBuffer m_vertPosBuffer;
    QOpenGLShaderProgram m_program;
    int m_uColorLocation;
    int m_uMvpMatrixLocation;
    QMatrix4x4 m_mvpMatrix;
    QMatrix4x4 m_projMatrix;
    QMatrix4x4 m_viewMatrix;
    QMatrix4x4 m_projViewMatrix;
    QMatrix4x4 m_modelMatrix;
    const float m_worldWidth = 200.f;
    const float m_worldHeight = 100.f;
    float m_worldAspect = m_worldHeight / m_worldWidth;
    int m_viewportX;
    int m_viewportY;
    int m_viewportWidth;
    int m_viewportHeight;
    float m_angleStep = 10.f;
    int m_amountOfDiskVertices = 360.f / m_angleStep + 2;
    bool m_mouseHolding = false;
    float m_diskPosX = 100.f;
    float m_diskPosY = 50.f;
};

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

[8Observer8]

Custom collision detection between two disks

WebAssembly demo on free Netlify hosting

custom-collision-detection-disks-opengles2-qt6-cpp.pro

QT += core gui openglwidgets

CONFIG += c++17

SOURCES += \
    main.cpp

main.cpp

#include <QtMath>
#include <QtGui/QMatrix4x4>
#include <QtGui/QMouseEvent>
#include <QtGui/QOpenGLFunctions>
#include <QtGui/QSurfaceFormat>
#include <QtGui/QVector3D>
#include <QtGui/QVector4D>
#include <QtOpenGL/QOpenGLBuffer>
#include <QtOpenGL/QOpenGLShader>
#include <QtOpenGL/QOpenGLShaderProgram>
#include <QtOpenGL/QOpenGLWindow>
#include <QtWidgets/QApplication>

class OpenGLWindow : public QOpenGLWindow, private QOpenGLFunctions
{
public:
    OpenGLWindow()
    {
        setTitle("OpenGL ES 2.0, Qt6, C++");
        resize(500, 500);

        QSurfaceFormat surfaceFormat;
        surfaceFormat.setDepthBufferSize(24);
        surfaceFormat.setSamples(4);
        setFormat(surfaceFormat);
    }

    void initializeGL() override
    {
        initializeOpenGLFunctions();
        glClearColor(0.04f, 0.62f, 0.48f, 1.f);
        glEnable(GL_BLEND);
        glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

        QString vertShaderSrc =
            "attribute vec2 aPosition;\n"
            "uniform mat4 uMvpMatrix;"
            "void main()\n"
            "{\n"
            "    gl_Position = uMvpMatrix * vec4(aPosition, 0.0, 1.0);\n"
            "}\n";

        QString fragShaderSrc =
            "#ifdef GL_ES\n"
            "precision mediump float;\n"
            "#endif\n"
            "uniform vec4 uColor;\n"
            "void main()\n"
            "{\n"
            "    gl_FragColor = uColor;\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[m_amountOfDiskVertices * 2 + 8]; // Disk + Square
        float radius = 0.5f;
        float angle = 0.f;

        int index = 0;
        // Disk center
        vertPositions[index++] = 0.f;
        vertPositions[index++] = 0.f;

               // Disk
        for (int i = 0; i < m_amountOfDiskVertices - 1; i++)
        {
            float radians = qDegreesToRadians(angle);
            float x = radius * qCos(radians);
            float y = radius * qSin(radians);
            vertPositions[index++] = x;
            vertPositions[index++] = y;
            angle += m_angleStep;
        }
        // Square
        vertPositions[index++] = -0.5f;
        vertPositions[index++] = -0.5f;
        vertPositions[index++] = 0.5f;
        vertPositions[index++] = -0.5f;
        vertPositions[index++] = -0.5f;
        vertPositions[index++] = 0.5f;
        vertPositions[index++] = 0.5f;
        vertPositions[index++] = 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");

        m_uColorLocation = m_program.uniformLocation("uColor");
        m_uMvpMatrixLocation = m_program.uniformLocation("uMvpMatrix");
        m_viewMatrix.lookAt(QVector3D(0, 0, 1), QVector3D(0, 0, 0), QVector3D(0, 1, 0));
    }

    void resizeGL(int w, int h) override
    {
        int deviceW = w * devicePixelRatio();
        int deviceH = h * devicePixelRatio();
        float deviceAspect = deviceH / (float) deviceW;

        if (deviceAspect > m_worldAspect)
        {
            m_viewportWidth = deviceW;
            m_viewportHeight = (int) deviceW * m_worldAspect;
            m_viewportX = 0;
            m_viewportY = (int) (deviceH - m_viewportHeight) / 2.f;
        }
        else
        {
            m_viewportWidth = (int) deviceH / m_worldAspect;
            m_viewportHeight = deviceH;
            m_viewportX = (int) (deviceW - m_viewportWidth) / 2.f;
            m_viewportY = 0;
        }
        m_projMatrix.setToIdentity();
        m_projMatrix.ortho(0.f, m_worldWidth, 0.f, m_worldHeight, 1.f, -1.f);
        m_projViewMatrix = m_projMatrix * m_viewMatrix;
    }

    void paintGL() override
    {
        glClear(GL_COLOR_BUFFER_BIT);
        glClearColor(0.2, 0.2, 0.2, 1);
        glClear(GL_COLOR_BUFFER_BIT);
        glViewport(m_viewportX, m_viewportY, m_viewportWidth, m_viewportHeight);
        glScissor(m_viewportX, m_viewportY, m_viewportWidth, m_viewportHeight);
        glClearColor(0.04, 0.62, 0.48, 1);
        glEnable(GL_SCISSOR_TEST);
        glClear(GL_COLOR_BUFFER_BIT);
        glDisable(GL_SCISSOR_TEST);

        m_disk2Color.setW(0.2f);
        if (dist(m_disk1PosX, m_disk1PosY, m_disk2PosX, m_disk2PosY) < 30.f)
            m_disk2Color.setW(1.f);

        // Disk
        drawDisk(m_disk2PosX, m_disk2PosY, 30.f, m_disk2Color);
        // Disk
        drawDisk(m_disk1PosX, m_disk1PosY, 30.f, QVector4D(0.f, 0.f, 0.5f, 1.f));
        // Left border
        drawRectangle(5.f, 50.f, 5.f, 85.f, 0.f, QVector4D(0.62f, 0.04f, 0.18f, 1.f));
        // Right border
        drawRectangle(195.f, 50.f, 5.f, 85.f, 0.f, QVector4D(0.62f, 0.04f, 0.18f, 1.f));
        // Top border
        drawRectangle(100.f, 95.f, 185.f, 5.f, 0.f, QVector4D(0.62f, 0.04f, 0.18f, 1.f));
        // Bottom border
        drawRectangle(100.f, 5.f, 185.f, 5.f, 0.f, QVector4D(0.62f, 0.04f, 0.18f, 1.f));
    }

    float dist(float x1, float y1, float x2, float y2)
    {
        float deltaX = qFabs(x1 - x2);
        float deltaY = qFabs(y1 - y2);
        return qSqrt(qPow(deltaX, 2) + qPow(deltaY, 2));
    }

    void drawDisk(float x, float y, float diameter, const QVector4D& color)
    {
        m_modelMatrix.setToIdentity();
        m_modelMatrix.translate(QVector3D(x, y, 0));
        m_modelMatrix.scale(QVector3D(diameter, diameter, 1));
        m_mvpMatrix = m_projViewMatrix * m_modelMatrix;
        m_program.setUniformValue(m_uMvpMatrixLocation, m_mvpMatrix);
        m_program.setUniformValue(m_uColorLocation, color);
        glDrawArrays(GL_TRIANGLE_FAN, 0, m_amountOfDiskVertices);
    }

    void drawRectangle(float x, float y, float w, float h,
        float angle, const QVector4D& color)
    {
        m_modelMatrix.setToIdentity();
        m_modelMatrix.translate(QVector3D(x, y, 0));
        m_modelMatrix.rotate(angle, QVector3D(0, 0, 1));
        m_modelMatrix.scale(QVector3D(w, h, 1));
        m_mvpMatrix = m_projViewMatrix * m_modelMatrix;
        m_program.setUniformValue(m_uMvpMatrixLocation, m_mvpMatrix);
        m_program.setUniformValue(m_uColorLocation, color);
        glDrawArrays(GL_TRIANGLE_STRIP, m_amountOfDiskVertices, 4);
    }

    void mousePressEvent(QMouseEvent *event) override
    {
        switch (event->button()) {
            case Qt::MouseButton::LeftButton:
            {
                m_mouseHolding = true;
                int x = event->pos().x() * devicePixelRatio();
                int y = (height() - event->pos().y() - 1) * devicePixelRatio();
                if ((m_viewportX <= x && x < (m_viewportX + m_viewportWidth)) &&
                    (m_viewportY <= y && y < (m_viewportY + m_viewportHeight)))
                {
                    float normalizedX = (x - m_viewportX) / (float) m_viewportWidth;
                    float normalizedY = (y - m_viewportY) / (float) m_viewportHeight;
                    m_disk1PosX = m_worldWidth * normalizedX;
                    m_disk1PosY = m_worldHeight * normalizedY;
                }
                update();
                break;
            }
            default:
                break;
        }
    }

    void mouseMoveEvent(QMouseEvent *event) override
    {
        if (!m_mouseHolding)
            return;

        int x = event->pos().x() * devicePixelRatio();
        int y = (height() - event->pos().y() - 1) * devicePixelRatio();
        if ((m_viewportX <= x && x < (m_viewportX + m_viewportWidth)) &&
            (m_viewportY <= y && y < (m_viewportY + m_viewportHeight)))
        {
            float normalizedX = (x - m_viewportX) / (float) m_viewportWidth;
            float normalizedY = (y - m_viewportY) / (float) m_viewportHeight;
            m_disk1PosX = m_worldWidth * normalizedX;
            m_disk1PosY = m_worldHeight * normalizedY;
        }
        update();
    }

    void mouseReleaseEvent(QMouseEvent *event) override
    {
        switch (event->button()) {
            case Qt::MouseButton::LeftButton:
            {
                m_mouseHolding = false;
                break;
            }
            default:
                break;
        }
    }

private:
    QOpenGLBuffer m_vertPosBuffer;
    QOpenGLShaderProgram m_program;
    int m_uColorLocation;
    int m_uMvpMatrixLocation;
    QMatrix4x4 m_mvpMatrix;
    QMatrix4x4 m_projMatrix;
    QMatrix4x4 m_viewMatrix;
    QMatrix4x4 m_projViewMatrix;
    QMatrix4x4 m_modelMatrix;
    const float m_worldWidth = 200.f;
    const float m_worldHeight = 100.f;
    float m_worldAspect = m_worldHeight / m_worldWidth;
    int m_viewportX;
    int m_viewportY;
    int m_viewportWidth;
    int m_viewportHeight;
    float m_angleStep = 10.f;
    int m_amountOfDiskVertices = 360.f / m_angleStep + 2;
    bool m_mouseHolding = false;
    float m_disk1PosX = 150.f;
    float m_disk1PosY = 50.f;
    QVector4D m_disk2Color = QVector4D(0.8f, 0.f, 0.f, 0.2f);
    float m_disk2PosX = 70.f;
    float m_disk2PosY = 50.f;
};

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

[8Observer8]

Lines with thickness with disks between them

This example draws two lines from "start" to "finish" with thickness:

void drawLine(const QVector2D &from, const QVector2D &to, float thickness,
    const QVector3D& color)

It draws a rectangle. I place three disks: in the start point, between lines (where lines are connected), and in the finish point:

        // Strip line
        // Disk
        QVector3D lineColor(0.25f, 0.31f, 0.85f);
        drawDisk(20.f, 50.f, 10.f, lineColor);
        // Line
        drawLine(QVector2D(20.f, 50.f), QVector2D(50.f, 70.f), 10.f, lineColor);
        // Disk
        drawDisk(50.f, 70.f, 10.f, lineColor);
        // Line
        drawLine(QVector2D(50.f, 70.f), QVector2D(60.f, 20.f), 10.f, lineColor);
        // Disk
        drawDisk(60.f, 20.f, 10.f, lineColor);

WebAssembly demo on free Netlify hosting

lines-with-thickness-opengles2-qt6-cpp.pro

QT += core gui openglwidgets

CONFIG += c++17

SOURCES += \
    main.cpp

main.cpp

#include <QtMath>
#include <QtGui/QMatrix4x4>
#include <QtGui/QOpenGLFunctions>
#include <QtGui/QQuaternion>
#include <QtGui/QSurfaceFormat>
#include <QtGui/QVector2D>
#include <QtGui/QVector3D>
#include <QtOpenGL/QOpenGLBuffer>
#include <QtOpenGL/QOpenGLShader>
#include <QtOpenGL/QOpenGLShaderProgram>
#include <QtOpenGL/QOpenGLWindow>
#include <QtWidgets/QApplication>

class OpenGLWindow : public QOpenGLWindow, private QOpenGLFunctions
{
public:
    OpenGLWindow()
    {
        setTitle("OpenGL ES 2.0, Qt6, C++");
        resize(450, 450);

        QSurfaceFormat surfaceFormat;
        surfaceFormat.setDepthBufferSize(24);
        surfaceFormat.setSamples(4);
        setFormat(surfaceFormat);
    }

    void initializeGL() override
    {
        initializeOpenGLFunctions();
        glClearColor(0.04f, 0.62f, 0.48f, 1.f);

        QString vertShaderSrc =
            "attribute vec2 aPosition;\n"
            "uniform mat4 uMvpMatrix;"
            "void main()\n"
            "{\n"
            "    gl_Position = uMvpMatrix * vec4(aPosition, 0.0, 1.0);\n"
            "}\n";

        QString fragShaderSrc =
            "#ifdef GL_ES\n"
            "precision mediump float;\n"
            "#endif\n"
            "uniform vec3 uColor;\n"
            "void main()\n"
            "{\n"
            "    gl_FragColor = vec4(uColor, 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[m_amountOfDiskVertices * 2 + 8]; // Disk + Square
        float radius = 0.5f;
        float angle = 0.f;

        int index = 0;
        // Disk center
        vertPositions[index++] = 0.f;
        vertPositions[index++] = 0.f;

        // Disk
        for (int i = 0; i < m_amountOfDiskVertices - 1; i++)
        {
            float radians = qDegreesToRadians(angle);
            float x = radius * qCos(radians);
            float y = radius * qSin(radians);
            vertPositions[index++] = x;
            vertPositions[index++] = y;
            angle += m_angleStep;
        }
        // Square
        vertPositions[index++] = -0.5f;
        vertPositions[index++] = -0.5f;
        vertPositions[index++] = 0.5f;
        vertPositions[index++] = -0.5f;
        vertPositions[index++] = -0.5f;
        vertPositions[index++] = 0.5f;
        vertPositions[index++] = 0.5f;
        vertPositions[index++] = 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");

        m_uColorLocation = m_program.uniformLocation("uColor");
        m_uMvpMatrixLocation = m_program.uniformLocation("uMvpMatrix");
        m_viewMatrix.lookAt(QVector3D(0, 0, 1), QVector3D(0, 0, 0), QVector3D(0, 1, 0));
    }

    void resizeGL(int w, int h) override
    {
        int deviceW = w * devicePixelRatio();
        int deviceH = h * devicePixelRatio();
        float deviceAspect = deviceH / (float) deviceW;

        if (deviceAspect > m_worldAspect)
        {
            m_viewportWidth = deviceW;
            m_viewportHeight = (int) deviceW * m_worldAspect;
            m_viewportX = 0;
            m_viewportY = (int) (deviceH - m_viewportHeight) / 2.f;
        }
        else
        {
            m_viewportWidth = (int) deviceH / m_worldAspect;
            m_viewportHeight = deviceH;
            m_viewportX = (int) (deviceW - m_viewportWidth) / 2.f;
            m_viewportY = 0;
        }
        m_projMatrix.setToIdentity();
        m_projMatrix.ortho(0.f, m_worldWidth, 0.f, m_worldHeight, 1.f, -1.f);
        m_projViewMatrix = m_projMatrix * m_viewMatrix;
    }

    void paintGL() override
    {
        glClear(GL_COLOR_BUFFER_BIT);
        glClearColor(0.82f, 0.87f, 0.97f, 1.f);
        glClear(GL_COLOR_BUFFER_BIT);
        glViewport(m_viewportX, m_viewportY, m_viewportWidth, m_viewportHeight);
        glScissor(m_viewportX, m_viewportY, m_viewportWidth, m_viewportHeight);
        glClearColor(0.82f, 0.87f, 0.97f, 1.f);
        glEnable(GL_SCISSOR_TEST);
        glClear(GL_COLOR_BUFFER_BIT);
        glDisable(GL_SCISSOR_TEST);

        // Strip line
        // Disk
        QVector3D lineColor(0.25f, 0.31f, 0.85f);
        drawDisk(20.f, 50.f, 10.f, lineColor);
        // Line
        drawLine(QVector2D(20.f, 50.f), QVector2D(50.f, 70.f), 10.f, lineColor);
        // Disk
        drawDisk(50.f, 70.f, 10.f, lineColor);
        // Line
        drawLine(QVector2D(50.f, 70.f), QVector2D(60.f, 20.f), 10.f, lineColor);
        // Disk
        drawDisk(60.f, 20.f, 10.f, lineColor);

        // Square
        drawRectangle(100.f, 50.f, 50.f, 50.f, 0.f, QVector3D(0.3f, 0.07f, 0.5f));
        // Disk
        drawDisk(100.f, 50.f, 50.f, QVector3D(0.8f, 0.8f, 0.5f));

        // Borders
        QVector3D borderColor(0.62f, 0.04f, 0.18f);
        // Left border
        drawRectangle(5.f, 50.f, 5.f, 85.f, 0.f, borderColor);
        // Right border
        drawRectangle(195.f, 50.f, 5.f, 85.f, 0.f, borderColor);
        // Top border
        drawRectangle(100.f, 95.f, 185.f, 5.f, 0.f, borderColor);
        // Bottom border
        drawRectangle(100.f, 5.f, 185.f, 5.f, 0.f, borderColor);
    }

    void drawDisk(float x, float y, float diameter, const QVector3D& color)
    {
        m_modelMatrix.setToIdentity();
        m_modelMatrix.translate(QVector3D(x, y, 0.f));
        m_modelMatrix.scale(QVector3D(diameter, diameter, 1.f));
        m_mvpMatrix = m_projViewMatrix * m_modelMatrix;
        m_program.setUniformValue(m_uMvpMatrixLocation, m_mvpMatrix);
        m_program.setUniformValue(m_uColorLocation, color);
        glDrawArrays(GL_TRIANGLE_FAN, 0, m_amountOfDiskVertices);
    }

    void drawRectangle(float x, float y, float w, float h,
        float angle, const QVector3D& color)
    {
        m_modelMatrix.setToIdentity();
        m_modelMatrix.translate(QVector3D(x, y, 0.f));
        m_modelMatrix.rotate(angle, QVector3D(0.f, 0.f, 1.f));
        m_modelMatrix.scale(QVector3D(w, h, 1.f));
        m_mvpMatrix = m_projViewMatrix * m_modelMatrix;
        m_program.setUniformValue(m_uMvpMatrixLocation, m_mvpMatrix);
        m_program.setUniformValue(m_uColorLocation, color);
        glDrawArrays(GL_TRIANGLE_STRIP, m_amountOfDiskVertices, 4);
    }

    void drawLine(const QVector2D &from, const QVector2D &to, float thickness,
        const QVector3D& color)
    {
        QVector2D center;

        if (from.x() > to.x())
        {
            center.setX(to.x() + qFabs(from.x() - to.x()) / 2.f);
        }
        else
        {
            center.setX(from.x() + qFabs(to.x() - from.x()) / 2.f);
        }

        if (from.y() > to.y())
        {
            center.setY(to.y() + qFabs(from.y() - to.y()) / 2.f);
        }
        else
        {
            center.setY(from.y() + qFabs(to.y() - from.y()) / 2.f);
        }

        QVector3D tempVec;
        tempVec.setX(to.x() - from.x());
        tempVec.setY(to.y() - from.y());
        float length = tempVec.length();
        tempVec.normalize();
        QQuaternion quat = QQuaternion::rotationTo(QVector3D(1.f, 0.f, 0.f), tempVec);

        m_modelMatrix.setToIdentity();
        m_modelMatrix.translate(QVector3D(center.x(), center.y(), 0.f));
        m_modelMatrix.rotate(quat);
        m_modelMatrix.scale(QVector3D(length, thickness, 1.f));
        m_mvpMatrix = m_projViewMatrix * m_modelMatrix;
        m_program.setUniformValue(m_uMvpMatrixLocation, m_mvpMatrix);
        m_program.setUniformValue(m_uColorLocation, color);
        glDrawArrays(GL_TRIANGLE_STRIP, m_amountOfDiskVertices, 4);
    }

private:
    QOpenGLBuffer m_vertPosBuffer;
    QOpenGLShaderProgram m_program;
    int m_uColorLocation;
    int m_uMvpMatrixLocation;
    QMatrix4x4 m_mvpMatrix;
    QMatrix4x4 m_projMatrix;
    QMatrix4x4 m_viewMatrix;
    QMatrix4x4 m_projViewMatrix;
    QMatrix4x4 m_modelMatrix;
    const float m_worldWidth = 200.f;
    const float m_worldHeight = 100.f;
    float m_worldAspect = m_worldHeight / m_worldWidth;
    int m_viewportX;
    int m_viewportY;
    int m_viewportWidth;
    int m_viewportHeight;
    int m_angleStep = 10;
    int m_amountOfDiskVertices = 360 / m_angleStep + 2;
};

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

[8Observer8]

Line drawer

Created a separate class for drawing a line.

WebAssembly demo on free Netlify hosting

line-drawer-opengles2-qt6-cpp.pro

QT += core gui openglwidgets

win32: LIBS += -lopengl32

CONFIG += c++17

SOURCES += \
    line_drawer.cpp \
    main.cpp \
    opengl_window.cpp

HEADERS += \
    line_drawer.h \
    opengl_window.h

main.cpp

#include <QtWidgets/QApplication>
#include "opengl_window.h"

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

line_drawer.h

#ifndef LINE_DRAWER
#define LINE_DRAWER

#include <QtGui/QMatrix4x4>
#include <QtGui/QVector2D>
#include <QtGui/QVector3D>
#include <QtOpenGL/QOpenGLBuffer>
#include <QtOpenGL/QOpenGLShaderProgram>

class LineDrawer
{
public:
    LineDrawer(QOpenGLShaderProgram *program);

    void draw(const QVector2D &from, const QVector2D &to,
        const QVector3D &color, float thickness = 1.f);
    void setProjViewMatrix(const QMatrix4x4 &projViewMatrix);

private:
    void bind();

private:
    QOpenGLShaderProgram *m_program;
    QOpenGLBuffer m_vertPosBuffer;
    int m_aPositionLocation;
    int m_uMvpMatrixLocation;
    int m_uColorLocation;
    QMatrix4x4 m_projViewMatrix;
    QMatrix4x4 m_modelMatrix;
    QMatrix4x4 m_mvpMatrix;
};

#endif // LINE_DRAWER

line_drawer.cpp

#include "line_drawer.h"

LineDrawer::LineDrawer(QOpenGLShaderProgram *program)
{
    m_program = program;
    m_program->bind();

    m_aPositionLocation = m_program->attributeLocation("aPosition");
    m_uMvpMatrixLocation = m_program->uniformLocation("uMvpMatrix");
    m_uColorLocation = m_program->uniformLocation("uColor");

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

void LineDrawer::setProjViewMatrix(const QMatrix4x4 &projViewMatrix)
{
    m_projViewMatrix = projViewMatrix;
}

void LineDrawer::bind()
{
    m_program->bind();
    m_vertPosBuffer.bind();
    m_program->setAttributeBuffer(m_aPositionLocation, GL_FLOAT, 0, 2);
    m_program->enableAttributeArray(m_aPositionLocation);
}

void LineDrawer::draw(const QVector2D &from, const QVector2D &to,
    const QVector3D &color, float thickness)
{
    bind();
    float centerX, centerY;
    QVector3D tempVec;

    if (from.x() > to.x())
    {
        centerX = to.x() + std::abs(from.x() - to.x()) / 2.f;
    }
    else
    {
        centerX = from.x() + std::abs(to.x() - from.x()) / 2.f;
    }

    if (from.y() > to.y())
    {
        centerY = to.y() + std::abs(from.y() - to.y()) / 2.f;
    }
    else
    {
        centerY = from.y() + std::abs(to.y() - from.y()) / 2.f;
    }

    tempVec.setX(to.x() - from.x());
    tempVec.setY(to.y() - from.y());
    float length = tempVec.length();
    tempVec.normalize();
    QQuaternion quat = QQuaternion::rotationTo(QVector3D(1, 0, 0), tempVec);

    m_modelMatrix.setToIdentity();
    m_modelMatrix.translate(QVector3D(centerX, centerY, 0));
    m_modelMatrix.rotate(quat);
    m_modelMatrix.scale(QVector3D(length, thickness, 1));
    m_mvpMatrix = m_projViewMatrix * m_modelMatrix;
    m_program->setUniformValue(m_uMvpMatrixLocation, m_mvpMatrix);
    m_program->setUniformValue(m_uColorLocation, color);
    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
}

opengl_window.h

#ifndef OPENGL_WINDOW_H
#define OPENGL_WINDOW_H

#include <QtMath>
#include <QtGui/QMatrix4x4>
#include <QtGui/QOpenGLFunctions>
#include <QtGui/QQuaternion>
#include <QtGui/QSurfaceFormat>
#include <QtGui/QVector2D>
#include <QtGui/QVector3D>
#include <QtOpenGL/QOpenGLShader>
#include <QtOpenGL/QOpenGLShaderProgram>
#include <QtOpenGL/QOpenGLWindow>

#include "line_drawer.h"

class OpenGLWindow : public QOpenGLWindow, private QOpenGLFunctions
{
public:
    OpenGLWindow();

    ~OpenGLWindow();

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

private:
    QOpenGLShaderProgram m_program;
    QMatrix4x4 m_projMatrix;
    QMatrix4x4 m_viewMatrix;
    QMatrix4x4 m_projViewMatrix;
    const float m_worldWidth = 200.f;
    const float m_worldHeight = 100.f;
    float m_worldAspect = m_worldHeight / m_worldWidth;
    int m_viewportX;
    int m_viewportY;
    int m_viewportWidth;
    int m_viewportHeight;
    LineDrawer *m_lineDrawer;
};

#endif // OPENGL_WINDOW_H

opengl_window.cpp

#include "opengl_window.h"

OpenGLWindow::OpenGLWindow()
{
    setTitle("OpenGL ES 2.0, Qt6, C++");
    resize(450, 450);

    QSurfaceFormat surfaceFormat;
    surfaceFormat.setDepthBufferSize(24);
    surfaceFormat.setSamples(4);
    setFormat(surfaceFormat);
}

OpenGLWindow::~OpenGLWindow()
{
    delete m_lineDrawer;
}

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

    QString vertShaderSrc =
        "attribute vec2 aPosition;\n"
        "uniform mat4 uMvpMatrix;"
        "void main()\n"
        "{\n"
        "    gl_Position = uMvpMatrix * vec4(aPosition, 0.0, 1.0);\n"
        "}\n";

    QString fragShaderSrc =
        "#ifdef GL_ES\n"
        "precision mediump float;\n"
        "#endif\n"
        "uniform vec3 uColor;\n"
        "void main()\n"
        "{\n"
        "    gl_FragColor = vec4(uColor, 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();

    m_lineDrawer = new LineDrawer(&m_program);

    m_viewMatrix.lookAt(QVector3D(0, 0, 1), QVector3D(0, 0, 0), QVector3D(0, 1, 0));
}

void OpenGLWindow::resizeGL(int w, int h)
{
    int deviceW = w * devicePixelRatio();
    int deviceH = h * devicePixelRatio();
    float deviceAspect = deviceH / (float) deviceW;

    if (deviceAspect > m_worldAspect)
    {
        m_viewportWidth = deviceW;
        m_viewportHeight = (int) deviceW * m_worldAspect;
        m_viewportX = 0;
        m_viewportY = (int) (deviceH - m_viewportHeight) / 2.f;
    }
    else
    {
        m_viewportWidth = (int) deviceH / m_worldAspect;
        m_viewportHeight = deviceH;
        m_viewportX = (int) (deviceW - m_viewportWidth) / 2.f;
        m_viewportY = 0;
    }
    m_projMatrix.setToIdentity();
    m_projMatrix.ortho(0.f, m_worldWidth, 0.f, m_worldHeight, 1.f, -1.f);
    m_projViewMatrix = m_projMatrix * m_viewMatrix;

    m_lineDrawer->setProjViewMatrix(m_projViewMatrix);
}

void OpenGLWindow::paintGL()
{
    glClear(GL_COLOR_BUFFER_BIT);
    glClearColor(0.82f, 0.87f, 0.97f, 1.f);
    glClear(GL_COLOR_BUFFER_BIT);
    glViewport(m_viewportX, m_viewportY, m_viewportWidth, m_viewportHeight);
    glScissor(m_viewportX, m_viewportY, m_viewportWidth, m_viewportHeight);
    glClearColor(0.82f, 0.87f, 0.97f, 1.f);
    glEnable(GL_SCISSOR_TEST);
    glClear(GL_COLOR_BUFFER_BIT);
    glDisable(GL_SCISSOR_TEST);

    // X axis
    QVector3D xAxisColor(0.80f, 0.15f, 0.18f);
    m_lineDrawer->draw(QVector2D(30.f, 20.f), QVector2D(170.f, 20.f), xAxisColor);
    // Arrow
    m_lineDrawer->draw(QVector2D(165.f, 23.f), QVector2D(170.f, 20.f), xAxisColor);
    m_lineDrawer->draw(QVector2D(165.f, 17.f), QVector2D(170.f, 20.f),xAxisColor);
    // Divisions
    m_lineDrawer->draw(QVector2D(50.f, 17.f), QVector2D(50.f, 23.f), xAxisColor);
    m_lineDrawer->draw(QVector2D(70.f, 17.f), QVector2D(70.f, 23.f), xAxisColor);
    m_lineDrawer->draw(QVector2D(90.f, 17.f), QVector2D(90.f, 23.f), xAxisColor);
    m_lineDrawer->draw(QVector2D(110.f, 17.f), QVector2D(110.f, 23.f), xAxisColor);
    m_lineDrawer->draw(QVector2D(130.f, 17.f), QVector2D(130.f, 23.f), xAxisColor);
    m_lineDrawer->draw(QVector2D(150.f, 17.f), QVector2D(150.f, 23.f), xAxisColor);

    // Y axis
    QVector3D yAxisColor(0.20f, 0.60f, 0.30f);
    m_lineDrawer->draw(QVector2D(30.f, 20.f), QVector2D(30.f, 95.f), yAxisColor);
    // Arrow
    m_lineDrawer->draw(QVector2D(27.f, 90.f), QVector2D(30.f, 95.f), yAxisColor);
    m_lineDrawer->draw(QVector2D(33.f, 90.f), QVector2D(30.f, 95.f), yAxisColor);
    // Divisions
    m_lineDrawer->draw(QVector2D(27.f, 40.f), QVector2D(33.f, 40.f), yAxisColor);
    m_lineDrawer->draw(QVector2D(27.f, 60.f), QVector2D(33.f, 60.f), yAxisColor);
    m_lineDrawer->draw(QVector2D(27.f, 80.f), QVector2D(33.f, 80.f), yAxisColor);

    // Graph
    QVector3D graphColor(0.25f, 0.31f, 0.85f);
    m_lineDrawer->draw(QVector2D(50.f, 40.f), QVector2D(70.f, 60.f), graphColor);
    m_lineDrawer->draw(QVector2D(70.f, 60.f), QVector2D(130.f, 60.f), graphColor);
    m_lineDrawer->draw(QVector2D(130.f, 60.f), QVector2D(150.f, 80.f), graphColor);
}

[8Observer8]

Rectangle drawer

WebAssembly demo on free Netlify hosting

rectangle-drawer-opengles2-qt6-cpp.pro

QT += core gui openglwidgets

win32: LIBS += -lopengl32

CONFIG += c++17

SOURCES += \
    main.cpp \
    opengl_window.cpp \
    rectangle_drawer.cpp

HEADERS += \
    opengl_window.h \
    rectangle_drawer.h

main.cpp

#include <QtWidgets/QApplication>
#include "opengl_window.h"

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

rectangle_drawer.h

#ifndef RECTANGLE_DRAWER
#define RECTANGLE_DRAWER

#include <QtGui/QMatrix4x4>
#include <QtGui/QVector2D>
#include <QtGui/QVector3D>
#include <QtOpenGL/QOpenGLBuffer>
#include <QtOpenGL/QOpenGLShaderProgram>

class RectangleDrawer
{
public:
    RectangleDrawer(QOpenGLShaderProgram *program);

    void draw(const QVector2D &position, const QVector2D &size,
        const QVector3D &color, float angle = 0.f);
    void setProjViewMatrix(const QMatrix4x4 &projViewMatrix);

private:
    void bind();

private:
    QOpenGLShaderProgram *m_program;
    QOpenGLBuffer m_vertPosBuffer;
    int m_aPositionLocation;
    int m_uMvpMatrixLocation;
    int m_uColorLocation;
    QMatrix4x4 m_projViewMatrix;
    QMatrix4x4 m_modelMatrix;
    QMatrix4x4 m_mvpMatrix;
};

#endif // RECTANGLE_DRAWER

rectangle_drawer.cpp

#include "rectangle_drawer.h"

RectangleDrawer::RectangleDrawer(QOpenGLShaderProgram *program)
{
    m_program = program;
    m_program->bind();

    m_aPositionLocation = m_program->attributeLocation("aPosition");
    m_uMvpMatrixLocation = m_program->uniformLocation("uMvpMatrix");
    m_uColorLocation = m_program->uniformLocation("uColor");

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

void RectangleDrawer::setProjViewMatrix(const QMatrix4x4 &projViewMatrix)
{
    m_projViewMatrix = projViewMatrix;
}

void RectangleDrawer::bind()
{
    m_program->bind();
    m_vertPosBuffer.bind();
    m_program->setAttributeBuffer(m_aPositionLocation, GL_FLOAT, 0, 2);
    m_program->enableAttributeArray(m_aPositionLocation);
}

void RectangleDrawer::draw(const QVector2D &position, const QVector2D &size,
    const QVector3D &color, float angle)
{
    bind();
    m_modelMatrix.setToIdentity();
    m_modelMatrix.translate(QVector3D(position.x(), position.y(), 0.f));
    m_modelMatrix.rotate(angle, QVector3D(0.f, 0.f, 1.f));
    m_modelMatrix.scale(QVector3D(size.x(), size.y(), 1.f));
    m_mvpMatrix = m_projViewMatrix * m_modelMatrix;
    m_program->setUniformValue(m_uMvpMatrixLocation, m_mvpMatrix);
    m_program->setUniformValue(m_uColorLocation, color);
    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
}

opengl_window.h

#ifndef OPENGL_WINDOW
#define OPENGL_WINDOW

#include <QtMath>
#include <QtGui/QMatrix4x4>
#include <QtGui/QOpenGLFunctions>
#include <QtGui/QQuaternion>
#include <QtGui/QSurfaceFormat>
#include <QtGui/QVector2D>
#include <QtGui/QVector3D>
#include <QtOpenGL/QOpenGLShader>
#include <QtOpenGL/QOpenGLShaderProgram>
#include <QtOpenGL/QOpenGLWindow>

#include "rectangle_drawer.h"

class OpenGLWindow : public QOpenGLWindow, private QOpenGLFunctions
{
public:
    OpenGLWindow();

    ~OpenGLWindow();

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

private:
    QOpenGLShaderProgram m_program;
    QMatrix4x4 m_projMatrix;
    QMatrix4x4 m_viewMatrix;
    QMatrix4x4 m_projViewMatrix;
    const float m_worldWidth = 200.f;
    const float m_worldHeight = 100.f;
    float m_worldAspect = m_worldHeight / m_worldWidth;
    int m_viewportX;
    int m_viewportY;
    int m_viewportWidth;
    int m_viewportHeight;
    RectangleDrawer *m_rectangleDrawer;
};

#endif // OPENGL_WINDOW

opengl_window.cpp

#include "opengl_window.h"

OpenGLWindow::OpenGLWindow()
{
    setTitle("OpenGL ES 2.0, Qt6, C++");
    resize(600, 300);

    QSurfaceFormat surfaceFormat;
    surfaceFormat.setDepthBufferSize(24);
    surfaceFormat.setSamples(4);
    setFormat(surfaceFormat);
}

OpenGLWindow::~OpenGLWindow()
{
    delete m_rectangleDrawer;
}

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

    QString vertShaderSrc =
        "attribute vec2 aPosition;\n"
        "uniform mat4 uMvpMatrix;"
        "void main()\n"
        "{\n"
        "    gl_Position = uMvpMatrix * vec4(aPosition, 0.0, 1.0);\n"
        "}\n";

    QString fragShaderSrc =
        "#ifdef GL_ES\n"
        "precision mediump float;\n"
        "#endif\n"
        "uniform vec3 uColor;\n"
        "void main()\n"
        "{\n"
        "    gl_FragColor = vec4(uColor, 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();

    m_rectangleDrawer = new RectangleDrawer(&m_program);

    m_viewMatrix.lookAt(QVector3D(0, 0, 1), QVector3D(0, 0, 0), QVector3D(0, 1, 0));
}

void OpenGLWindow::resizeGL(int w, int h)
{
    int deviceW = w * devicePixelRatio();
    int deviceH = h * devicePixelRatio();
    float deviceAspect = deviceH / (float) deviceW;

    if (deviceAspect > m_worldAspect)
    {
        m_viewportWidth = deviceW;
        m_viewportHeight = (int) deviceW * m_worldAspect;
        m_viewportX = 0;
        m_viewportY = (int) (deviceH - m_viewportHeight) / 2.f;
    }
    else
    {
        m_viewportWidth = (int) deviceH / m_worldAspect;
        m_viewportHeight = deviceH;
        m_viewportX = (int) (deviceW - m_viewportWidth) / 2.f;
        m_viewportY = 0;
    }
    m_projMatrix.setToIdentity();
    m_projMatrix.ortho(0.f, m_worldWidth, 0.f, m_worldHeight, 1.f, -1.f);
    m_projViewMatrix = m_projMatrix * m_viewMatrix;

    m_rectangleDrawer->setProjViewMatrix(m_projViewMatrix);
}

void OpenGLWindow::paintGL()
{
    glClear(GL_COLOR_BUFFER_BIT);
    glClearColor(0.2f, 0.2f, 0.2f, 1.f);
    // glClearColor(0.82f, 0.87f, 0.97f, 1.f);
    glClear(GL_COLOR_BUFFER_BIT);
    glViewport(m_viewportX, m_viewportY, m_viewportWidth, m_viewportHeight);
    glScissor(m_viewportX, m_viewportY, m_viewportWidth, m_viewportHeight);
    glClearColor(0.82f, 0.87f, 0.97f, 1.f);
    glEnable(GL_SCISSOR_TEST);
    glClear(GL_COLOR_BUFFER_BIT);
    glDisable(GL_SCISSOR_TEST);

    m_rectangleDrawer->draw(QVector2D(50.f, 70.f), QVector2D(72.f, 7.f),
        QVector3D(0.80f, 0.15f, 0.18f), -27.f);
    m_rectangleDrawer->draw(QVector2D(160.f, 50.f), QVector2D(70.f, 5.f),
        QVector3D(0.20f, 0.60f, 0.30f), 10.f);
    m_rectangleDrawer->draw(QVector2D(100.f, 15.f), QVector2D(150.f, 7.f),
        QVector3D(0.25f, 0.31f, 0.85f));
}

[8Observer8]

Disk drawer

WebAssembly demo on free Netlify hosting

disk-drawer-opengles2-qt6-cpp.pro

QT += core gui openglwidgets

win32: LIBS += -lopengl32

CONFIG += c++17

SOURCES += \
    disk_drawer.cpp \
    main.cpp \
    opengl_window.cpp

HEADERS += \
    disk_drawer.h \
    opengl_window.h

main.cpp

#include <QtWidgets/QApplication>
#include "opengl_window.h"

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

disk_drawer.h

#ifndef DISK_DRAWER
#define DISK_DRAWER

#include <QtGui/QMatrix4x4>
#include <QtGui/QVector2D>
#include <QtGui/QVector3D>
#include <QtOpenGL/QOpenGLBuffer>
#include <QtOpenGL/QOpenGLShaderProgram>

class DiskDrawer
{
public:
    DiskDrawer(QOpenGLShaderProgram *program);

    void draw(const QVector2D &position, float diameter,
        const QVector3D &color);
    void setProjViewMatrix(const QMatrix4x4 &projViewMatrix);

private:
    void bind();

private:
    QOpenGLShaderProgram *m_program;
    QOpenGLBuffer m_vertPosBuffer;
    int m_aPositionLocation;
    int m_uMvpMatrixLocation;
    int m_uColorLocation;
    QMatrix4x4 m_projViewMatrix;
    QMatrix4x4 m_modelMatrix;
    QMatrix4x4 m_mvpMatrix;
    int m_angleStep = 5;
    int m_amountOfDiskVertices = 360 / m_angleStep + 2;
};

#endif // DISK_DRAWER

disk_drawer.cpp

#include "disk_drawer.h"

DiskDrawer::DiskDrawer(QOpenGLShaderProgram *program)
{
    m_program = program;
    m_program->bind();

    m_aPositionLocation = m_program->attributeLocation("aPosition");
    m_uMvpMatrixLocation = m_program->uniformLocation("uMvpMatrix");
    m_uColorLocation = m_program->uniformLocation("uColor");

    float vertPositions[m_amountOfDiskVertices * 2];
    float radius = 0.5f;
    float angle = 0.f;
    int index = 0;

    // Disk center
    vertPositions[index++] = 0.f;
    vertPositions[index++] = 0.f;

    for (int i = 0; i < m_amountOfDiskVertices - 1; i++)
    {
        float radians = qDegreesToRadians(angle);
        float x = radius * qCos(radians);
        float y = radius * qSin(radians);
        vertPositions[index++] = x;
        vertPositions[index++] = y;
        angle += m_angleStep;
    }

    m_vertPosBuffer.create();
    m_vertPosBuffer.bind();
    m_vertPosBuffer.allocate(vertPositions, sizeof(vertPositions));
}

void DiskDrawer::setProjViewMatrix(const QMatrix4x4 &projViewMatrix)
{
    m_projViewMatrix = projViewMatrix;
}

void DiskDrawer::bind()
{
    m_program->bind();
    m_vertPosBuffer.bind();
    m_program->setAttributeBuffer(m_aPositionLocation, GL_FLOAT, 0, 2);
    m_program->enableAttributeArray(m_aPositionLocation);
}

void DiskDrawer::draw(const QVector2D &position, float diameter,
    const QVector3D &color)
{
    bind();
    m_modelMatrix.setToIdentity();
    m_modelMatrix.translate(QVector3D(position.x(), position.y(), 0.f));
    m_modelMatrix.scale(QVector3D(diameter, diameter, 1.f));
    m_mvpMatrix = m_projViewMatrix * m_modelMatrix;
    m_program->setUniformValue(m_uMvpMatrixLocation, m_mvpMatrix);
    m_program->setUniformValue(m_uColorLocation, color);
    glDrawArrays(GL_TRIANGLE_FAN, 0, m_amountOfDiskVertices);
}

opengl_window.h

#ifndef OPENGL_WINDOW
#define OPENGL_WINDOW

#include <QtMath>
#include <QtGui/QMatrix4x4>
#include <QtGui/QOpenGLFunctions>
#include <QtGui/QQuaternion>
#include <QtGui/QSurfaceFormat>
#include <QtGui/QVector2D>
#include <QtGui/QVector3D>
#include <QtOpenGL/QOpenGLShader>
#include <QtOpenGL/QOpenGLShaderProgram>
#include <QtOpenGL/QOpenGLWindow>

#include "disk_drawer.h"

class OpenGLWindow : public QOpenGLWindow, private QOpenGLFunctions
{
public:
    OpenGLWindow();

    ~OpenGLWindow();

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

private:
    QOpenGLShaderProgram m_program;
    QMatrix4x4 m_projMatrix;
    QMatrix4x4 m_viewMatrix;
    QMatrix4x4 m_projViewMatrix;
    const float m_worldWidth = 200.f;
    const float m_worldHeight = 100.f;
    float m_worldAspect = m_worldHeight / m_worldWidth;
    int m_viewportX;
    int m_viewportY;
    int m_viewportWidth;
    int m_viewportHeight;
    DiskDrawer *m_diskDrawer;
};

#endif // OPENGL_WINDOW

opengl_window.cpp

#include "opengl_window.h"

OpenGLWindow::OpenGLWindow()
{
    setTitle("OpenGL ES 2.0, Qt6, C++");
    resize(600, 300);

    QSurfaceFormat surfaceFormat;
    surfaceFormat.setDepthBufferSize(24);
    surfaceFormat.setSamples(4);
    setFormat(surfaceFormat);
}

OpenGLWindow::~OpenGLWindow()
{
    delete m_diskDrawer;
}

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

    QString vertShaderSrc =
        "attribute vec2 aPosition;\n"
        "uniform mat4 uMvpMatrix;"
        "void main()\n"
        "{\n"
        "    gl_Position = uMvpMatrix * vec4(aPosition, 0.0, 1.0);\n"
        "}\n";

    QString fragShaderSrc =
        "#ifdef GL_ES\n"
        "precision mediump float;\n"
        "#endif\n"
        "uniform vec3 uColor;\n"
        "void main()\n"
        "{\n"
        "    gl_FragColor = vec4(uColor, 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();

    m_diskDrawer = new DiskDrawer(&m_program);

    m_viewMatrix.lookAt(QVector3D(0, 0, 1), QVector3D(0, 0, 0), QVector3D(0, 1, 0));
}

void OpenGLWindow::resizeGL(int w, int h)
{
    int deviceW = w * devicePixelRatio();
    int deviceH = h * devicePixelRatio();
    float deviceAspect = deviceH / (float) deviceW;

    if (deviceAspect > m_worldAspect)
    {
        m_viewportWidth = deviceW;
        m_viewportHeight = (int) deviceW * m_worldAspect;
        m_viewportX = 0;
        m_viewportY = (int) (deviceH - m_viewportHeight) / 2.f;
    }
    else
    {
        m_viewportWidth = (int) deviceH / m_worldAspect;
        m_viewportHeight = deviceH;
        m_viewportX = (int) (deviceW - m_viewportWidth) / 2.f;
        m_viewportY = 0;
    }
    m_projMatrix.setToIdentity();
    m_projMatrix.ortho(0.f, m_worldWidth, 0.f, m_worldHeight, 1.f, -1.f);
    m_projViewMatrix = m_projMatrix * m_viewMatrix;

    m_diskDrawer->setProjViewMatrix(m_projViewMatrix);
}

void OpenGLWindow::paintGL()
{
    glClear(GL_COLOR_BUFFER_BIT);
    // glClearColor(0.2f, 0.2f, 0.2f, 1.f);
    glClearColor(0.82f, 0.87f, 0.97f, 1.f);
    glClear(GL_COLOR_BUFFER_BIT);
    glViewport(m_viewportX, m_viewportY, m_viewportWidth, m_viewportHeight);
    glScissor(m_viewportX, m_viewportY, m_viewportWidth, m_viewportHeight);
    glClearColor(0.82f, 0.87f, 0.97f, 1.f);
    glEnable(GL_SCISSOR_TEST);
    glClear(GL_COLOR_BUFFER_BIT);
    glDisable(GL_SCISSOR_TEST);

    m_diskDrawer->draw(QVector2D(50.f, 70.f), 40.f,
        QVector3D(0.80f, 0.15f, 0.18f));
    m_diskDrawer->draw(QVector2D(160.f, 50.f), 50.f,
        QVector3D(0.20f, 0.60f, 0.30f));
    m_diskDrawer->draw(QVector2D(100.f, 15.f), 20.f,
        QVector3D(0.25f, 0.31f, 0.85f));
}

[8Observer8]

Ring drawer using line drawer

The RingDrawer class uses the LineDrawer class to draw the segments of a ring. For example, for number of segments equals to 10:

void RingDrawer::draw(const QVector2D &center, float radius,
    const QVector3D &color, int numberOfSegments, float thickness)
{
    float angle = 0.f;
    const float angleStep = 360.f / numberOfSegments;

    float x = radius * qCos(qDegreesToRadians(angle));
    float y = radius * qSin(qDegreesToRadians(angle));
    QVector2D from(center.x() + x, center.y() + y);
    angle += angleStep;

    for (int i = 0; i < numberOfSegments; i++)
    {
        x = radius * qCos(qDegreesToRadians(angle));
        y = radius * qSin(qDegreesToRadians(angle));
        QVector2D to(center.x() + x, center.y() + y);
        m_lineDrawer->draw(from, to, color, thickness);
        angle += angleStep;
        from = to;
    }
}

For number of segments equals to 50: WebAssembly demo on free Netlify hosting

ring-drawer-opengles2-qt6-cpp.pro

QT += core gui openglwidgets

win32: LIBS += -lopengl32

CONFIG += c++17

SOURCES += \
    line_drawer.cpp \
    main.cpp \
    opengl_window.cpp \
    ring_drawer.cpp

HEADERS += \
    line_drawer.h \
    opengl_window.h \
    ring_drawer.h

main.cpp

#include <QtWidgets/QApplication>
#include "opengl_window.h"

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

ring_drawer.h

#ifndef RING_DRAWER
#define RING_DRAWER

#include "line_drawer.h"

class RingDrawer
{
public:
    RingDrawer(QOpenGLShaderProgram *program);
    ~RingDrawer();

    void draw(const QVector2D &center, float radius,
        const QVector3D &color, int numberOfSegments = 50,
        float thickness = 1.f);
    void setProjViewMatrix(const QMatrix4x4 &projViewMatrix);

private:
    LineDrawer *m_lineDrawer;
};

#endif // RING_DRAWER

ring_drawer.cpp

#include <QtMath>

#include "ring_drawer.h"

RingDrawer::RingDrawer(QOpenGLShaderProgram *program)
{
    m_lineDrawer = new LineDrawer(program);
}

RingDrawer::~RingDrawer()
{
    delete m_lineDrawer;
}

void RingDrawer::setProjViewMatrix(const QMatrix4x4 &projViewMatrix)
{
    m_lineDrawer->setProjViewMatrix(projViewMatrix);
}

void RingDrawer::draw(const QVector2D &center, float radius,
    const QVector3D &color, int numberOfSegments, float thickness)
{
    float angle = 0.f;
    const float angleStep = 360.f / numberOfSegments;

    float x = radius * qCos(qDegreesToRadians(angle));
    float y = radius * qSin(qDegreesToRadians(angle));
    QVector2D from(center.x() + x, center.y() + y);
    angle += angleStep;

    for (int i = 0; i < numberOfSegments; i++)
    {
        x = radius * qCos(qDegreesToRadians(angle));
        y = radius * qSin(qDegreesToRadians(angle));
        QVector2D to(center.x() + x, center.y() + y);
        m_lineDrawer->draw(from, to, color, thickness);
        angle += angleStep;
        from = to;
    }
}

opengl_window.h

#ifndef OPENGL_WINDOW
#define OPENGL_WINDOW

#include <QtMath>
#include <QtGui/QMatrix4x4>
#include <QtGui/QOpenGLFunctions>
#include <QtGui/QQuaternion>
#include <QtGui/QSurfaceFormat>
#include <QtGui/QVector2D>
#include <QtGui/QVector3D>
#include <QtOpenGL/QOpenGLShader>
#include <QtOpenGL/QOpenGLShaderProgram>
#include <QtOpenGL/QOpenGLWindow>

#include "ring_drawer.h"

class OpenGLWindow : public QOpenGLWindow, private QOpenGLFunctions
{
public:
    OpenGLWindow();

    ~OpenGLWindow();

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

private:
    QOpenGLShaderProgram m_program;
    QMatrix4x4 m_projMatrix;
    QMatrix4x4 m_viewMatrix;
    QMatrix4x4 m_projViewMatrix;
    const float m_worldWidth = 200.f;
    const float m_worldHeight = 100.f;
    float m_worldAspect = m_worldHeight / m_worldWidth;
    int m_viewportX;
    int m_viewportY;
    int m_viewportWidth;
    int m_viewportHeight;
    RingDrawer *m_ringDrawer;
};

#endif // OPENGL_WINDOW

opengl_window.cpp

#include "opengl_window.h"

OpenGLWindow::OpenGLWindow()
{
    setTitle("OpenGL ES 2.0, Qt6, C++");
    resize(600, 300);

    QSurfaceFormat surfaceFormat;
    surfaceFormat.setDepthBufferSize(24);
    surfaceFormat.setSamples(4);
    setFormat(surfaceFormat);
}

OpenGLWindow::~OpenGLWindow()
{
    delete m_ringDrawer;
}

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


    QString vertShaderSrc =
        "attribute vec2 aPosition;\n"
        "uniform mat4 uMvpMatrix;"
        "void main()\n"
        "{\n"
        "    gl_Position = uMvpMatrix * vec4(aPosition, 0.0, 1.0);\n"
        "}\n";

    QString fragShaderSrc =
        "#ifdef GL_ES\n"
        "precision mediump float;\n"
        "#endif\n"
        "uniform vec3 uColor;\n"
        "void main()\n"
        "{\n"
        "    gl_FragColor = vec4(uColor, 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();

    m_ringDrawer = new RingDrawer(&m_program);

    m_viewMatrix.lookAt(QVector3D(0, 0, 1), QVector3D(0, 0, 0), QVector3D(0, 1, 0));
}

void OpenGLWindow::resizeGL(int w, int h)
{
    int deviceW = w * devicePixelRatio();
    int deviceH = h * devicePixelRatio();
    float deviceAspect = deviceH / (float) deviceW;

    if (deviceAspect > m_worldAspect)
    {
        m_viewportWidth = deviceW;
        m_viewportHeight = (int) deviceW * m_worldAspect;
        m_viewportX = 0;
        m_viewportY = (int) (deviceH - m_viewportHeight) / 2.f;
    }
    else
    {
        m_viewportWidth = (int) deviceH / m_worldAspect;
        m_viewportHeight = deviceH;
        m_viewportX = (int) (deviceW - m_viewportWidth) / 2.f;
        m_viewportY = 0;
    }
    m_projMatrix.setToIdentity();
    m_projMatrix.ortho(0.f, m_worldWidth, 0.f, m_worldHeight, 1.f, -1.f);
    m_projViewMatrix = m_projMatrix * m_viewMatrix;

    m_ringDrawer->setProjViewMatrix(m_projViewMatrix);
}

void OpenGLWindow::paintGL()
{
    glClear(GL_COLOR_BUFFER_BIT);
    // glClearColor(0.2f, 0.2f, 0.2f, 1.f);
    glClearColor(0.82f, 0.87f, 0.97f, 1.f);
    glClear(GL_COLOR_BUFFER_BIT);
    glViewport(m_viewportX, m_viewportY, m_viewportWidth, m_viewportHeight);
    glScissor(m_viewportX, m_viewportY, m_viewportWidth, m_viewportHeight);
    glClearColor(0.82f, 0.87f, 0.97f, 1.f);
    glEnable(GL_SCISSOR_TEST);
    glClear(GL_COLOR_BUFFER_BIT);
    glDisable(GL_SCISSOR_TEST);

    m_ringDrawer->draw(QVector2D(50.f, 70.f), 20.f,
        QVector3D(0.80f, 0.15f, 0.18f));
    m_ringDrawer->draw(QVector2D(160.f, 50.f), 25.f,
        QVector3D(0.20f, 0.60f, 0.30f));
    m_ringDrawer->draw(QVector2D(100.f, 15.f), 10.f,
        QVector3D(0.25f, 0.31f, 0.85f));
}

line_drawer.h

#ifndef LINE_DRAWER
#define LINE_DRAWER

#include <QtGui/QMatrix4x4>
#include <QtGui/QVector2D>
#include <QtGui/QVector3D>
#include <QtOpenGL/QOpenGLBuffer>
#include <QtOpenGL/QOpenGLShaderProgram>

class LineDrawer
{
public:
    LineDrawer(QOpenGLShaderProgram *program);

    void draw(const QVector2D &from, const QVector2D &to,
        const QVector3D &color, float thickness = 1.f);
    void setProjViewMatrix(const QMatrix4x4 &projViewMatrix);

private:
    void bind();

private:
    QOpenGLShaderProgram *m_program;
    QOpenGLBuffer m_vertPosBuffer;
    int m_aPositionLocation;
    int m_uMvpMatrixLocation;
    int m_uColorLocation;
    QMatrix4x4 m_projViewMatrix;
    QMatrix4x4 m_modelMatrix;
    QMatrix4x4 m_mvpMatrix;
};

#endif // LINE_DRAWER

line_drawer.cpp

#include "line_drawer.h"

LineDrawer::LineDrawer(QOpenGLShaderProgram *program)
{
    m_program = program;
    m_program->bind();

    m_aPositionLocation = m_program->attributeLocation("aPosition");
    m_uMvpMatrixLocation = m_program->uniformLocation("uMvpMatrix");
    m_uColorLocation = m_program->uniformLocation("uColor");

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

void LineDrawer::setProjViewMatrix(const QMatrix4x4 &projViewMatrix)
{
    m_projViewMatrix = projViewMatrix;
}

void LineDrawer::bind()
{
    m_program->bind();
    m_vertPosBuffer.bind();
    m_program->setAttributeBuffer(m_aPositionLocation, GL_FLOAT, 0, 2);
    m_program->enableAttributeArray(m_aPositionLocation);
}

void LineDrawer::draw(const QVector2D &from, const QVector2D &to,
    const QVector3D &color, float thickness)
{
    bind();
    float centerX, centerY;
    QVector3D tempVec;

    if (from.x() > to.x())
    {
        centerX = to.x() + std::abs(from.x() - to.x()) / 2.f;
    }
    else
    {
        centerX = from.x() + std::abs(to.x() - from.x()) / 2.f;
    }

    if (from.y() > to.y())
    {
        centerY = to.y() + std::abs(from.y() - to.y()) / 2.f;
    }
    else
    {
        centerY = from.y() + std::abs(to.y() - from.y()) / 2.f;
    }

    tempVec.setX(to.x() - from.x());
    tempVec.setY(to.y() - from.y());
    float length = tempVec.length();
    tempVec.normalize();
    QQuaternion quat = QQuaternion::rotationTo(QVector3D(1, 0, 0), tempVec);

    m_modelMatrix.setToIdentity();
    m_modelMatrix.translate(QVector3D(centerX, centerY, 0));
    m_modelMatrix.rotate(quat);
    m_modelMatrix.scale(QVector3D(length, thickness, 1));
    m_mvpMatrix = m_projViewMatrix * m_modelMatrix;
    m_program->setUniformValue(m_uMvpMatrixLocation, m_mvpMatrix);
    m_program->setUniformValue(m_uColorLocation, color);
    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
}

[8Observer8]

Orbit controls

I have created the OrbitControls class to pan a camera with right mouse button, rotate with the left mouse button, and zoom in/out with the wheel:

WebAssembly demo on free Netlify hosting

It is not ready to pan and zoom in/out on Android, rotation only:

Source code for QOpenGLWindow, Qt6, C++

[8Observer8]

How to set up Box2D in Qt Creator from sources for build for Android, Desktop, and WebAssembly

I have recorded this video today. But I don't like it. The voice is too low. I will make another video later and I will delete this one.

https://www.youtube.com/watch?v=OE4OOPQC7Nk

[8Observer8]

Detecting a mobile browser with Qt WebAssembly (topic)

It is important to determine whether a WebAssembly game is running on a mobile device or a personal computer in order to show or hide the joystick.

#ifdef Q_OS_WASM
#include <emscripten.h>
#endif

#include "widget.h"

#ifdef Q_OS_WASM
EM_JS(bool, isMobile, (), {
    return /iPhone|iPad|iPod|Android/i.test(navigator.userAgent);
})
#endif

Widget::Widget(QWidget *parent)
    : QWidget(parent)
{
    bool isMobile = false;

#ifdef Q_OS_WASM
    isMobile = isMobile();
#endif

#if defined Q_OS_ANDROID || defined Q_OS_IOS
    isMobile = true;
#endif

    qDebug() << "isMobile:" << isMobile;
}

Don't forget to add wasm: here:

QT += core gui widgets

CONFIG += c++17

wasm: INCLUDEPATH += "C:\emsdk\upstream\emscripten\cache\sysroot\include"

SOURCES += \
    main.cpp \
    widget.cpp

HEADERS += \
    widget.h

[8Observer8]

Get data with Qt client from deployed Node.js server using WebSockets (topic)

My following Qt 6.6.3 example works on Android, Desktop, and Web (with Qt WebAssembly). It prints data received from the server. The server contains the Box2D-WASM library. It sends the gravity value in JSON format when a client is connected. It is useful example to make multiplayer games with physics on the server side. I have deployed the example on free Glitch hosting: https://glitch.com/edit/#!/merciful-regal-soursop from the GitHub repository: send-gravity-from-server-to-client-box2d-wasm-js The client contains only one main.cpp file. It outputs the following information to the console:

connected
"{\"action\":\"scGravity\",\"data\":\"{\\\"x\\\":0,\\\"y\\\":-3}\"}"

You should download OpenSSL to run the following example on Android. Open the following window in Qt Creator (Edit > Preferences... > Devices > Android):

Add the following path to your pro-file:

QT += core gui websockets widgets

android: include(C:/Qt/Tools/OpenSSL-1.1.1j/Win_x64/bin/openssl.pri)

CONFIG += c++17

SOURCES += \
    main.cpp

Read how to add OpenSSL to your CMake project if you use CMake instead of QMake in the Qt documentaion: Adding OpenSSL Support for Android

Build the following example for Android, Desktop, and WebAssembly (I have tested it):

main.cpp

#include <QtNetwork/QNetworkRequest>
#include <QtWebSockets/QWebSocket>
#include <QtWidgets/QApplication>
#include <QtWidgets/QWidget>

class Widget : public QWidget
{
    Q_OBJECT

public:
    Widget()
    {
        setWindowTitle("Show gravity from server with Box2D-WASM");
        resize(420, 200);

        connect(&m_webSocket, &QWebSocket::connected,
            this, &Widget::onConnected);
        connect(&m_webSocket, &QWebSocket::textMessageReceived,
            this, &Widget::onMessageReceived);
        connect(&m_webSocket, &QWebSocket::errorOccurred,
            this, &Widget::onErrorOccurred);

        QUrl url("wss://merciful-regal-soursop.glitch.me");

        QNetworkRequest request;
        request.setUrl(url);
        request.setRawHeader(QByteArray("User-Agent"),
            QByteArray("Mozilla/5.0 "
                       "(Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) "
                       "Chrome/124.0.0.0 Safari/537.36"));

        m_webSocket.open(request);
    }

private slots:

    void onConnected()
    {
        qDebug() << "connected";
    }
    void onMessageReceived(const QString &message)
    {
        qDebug() << message;
    }

    void onErrorOccurred(QAbstractSocket::SocketError error)
    {
        qDebug() << "!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!";
        qDebug() << "Error:" << error;
        qDebug() << "Device supports OpenSSL:" << QSslSocket::supportsSsl();
        qDebug() << "!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!";
    }

private:
    QWebSocket m_webSocket;
};

#include "main.moc"

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

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How to set up PyOpenAL

PyOpenAL (released Dec 17, 2019): https://pypi.org/project/PyOpenAL/

pip install PyOpenAL

You can use original OpenAL API but PyOpenAL has a helpful wrapper functions. If your audio file plays with problems try to open it in the Audacity and export it with Encoding: Signed 16-bit PCM:

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Play sound by button click with PyOpenAL

pip install PyOpenAL PySide6

import sys

from openal import oalOpen
from PySide6.QtWidgets import QApplication, QPushButton, QWidget


class Widget(QWidget):

    def __init__(self):
        super().__init__()
        self.setWindowTitle("PyOpenAL, PySide6")
        self.resize(300, 150)

        self.btn = QPushButton("Play Sound", self)
        self.btn.clicked.connect(self.onPlay)

        self.source = oalOpen("assets/bounce.wav")
    
    def onPlay(self):
        self.source.play()

if __name__ == "__main__":
    app = QApplication(sys.argv)
    w = Widget()
    w.show()
    sys.exit(app.exec())

These are the Audacity settings when exporting an audio file. By default for PyOpenAL it must be "Encoding: Signed 16-bit PCM":

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Music volume slider

pip install PyOpenAL PySide6

The free audio file from itch is used in this example.

import sys

from openal import oalOpen, oalQuit
from PySide6.QtCore import Qt
from PySide6.QtWidgets import (QApplication, QCheckBox, QHBoxLayout, QPushButton,
                             QSlider, QVBoxLayout, QWidget)


class Widget(QWidget):

    def __init__(self):
        super().__init__()
        self.setWindowTitle("PyOpenAL, PySide6")
        self.resize(300, 150)

        # Music check box
        playMusic = QCheckBox("Play music")
        # playMusic.toggle()
        # print(playMusic.isChecked())
        playMusic.stateChanged.connect(self.onPlayMusic)

        # Sound button
        playSoundButton = QPushButton("Play sound")
        playSoundButton.clicked.connect(self.onPlaySound)

        mousicVolume = 0.1

        # Volume slider
        volumeSlider = QSlider(Qt.Orientation.Horizontal)
        volumeSlider.setValue(int(mousicVolume * 100))
        volumeSlider.valueChanged[int].connect(self.onChangeVolume)

        self.mousicSource = oalOpen("assets/infant_tour.wav")
        self.soundSource = oalOpen("assets/bounce.wav")
        self.mousicSource.set_gain(mousicVolume)

        self.mousicSource.set_looping(True)

        vbox = QVBoxLayout()
        vbox.addWidget(volumeSlider)
        vbox.addWidget(playMusic)
        vbox.addWidget(playSoundButton)
        vbox.addStretch(1)

        hbox = QHBoxLayout()
        hbox.addLayout(vbox)
        hbox.addStretch(1)
        self.setLayout(hbox)

    def onPlayMusic(self, state):
        
        if state == Qt.CheckState.Checked.value:
            self.mousicSource.play()
        else:
            self.mousicSource.pause()

    def onPlaySound(self):
        self.soundSource.play()

    def onChangeVolume(self, value):
        self.mousicSource.set_gain(value / 100)

    def closeEvent(self, event):
        oalQuit()

if __name__ == "__main__":
    app = QApplication(sys.argv)
    w = Widget()
    w.show()
    sys.exit(app.exec())

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Custom OpenGL button for WebAssembly and Android

You cannot make the standard Qt button for WebAssembly because of this bug: https://bugreports.qt.io/browse/QTBUG-120651 (you can use the patch from the "Gerrit Reviews") But OpenGL allows to make custom GUI elements.

WebAssembly demo on free Netlify hosting (QOpenGLWindow)

QOpenGLWindow works on Android 7.1.2 in the mobile browser without problems. You can find a lot of GUI game assets on itch: https://itch.io/game-assets/tag-gui I use the following GUI game asset in this demo: https://wenrexa.itch.io/holoui I have used Free Texture Packer to pack to button textures to one texture + json-file. Text was added in GIMP.

Source code for Qt6 C++

The same demo for SDL3:

Click buttons with color ID using glReadPixels

Demo in the browser

This example uses the following GUI asset: https://wenrexa.itch.io/holoui. You can find a lot of GUI assets on itch: https://itch.io/game-assets/tag-gui I packed the GUI textures using Free Texture Packer to one texture + JSON. RapidJSON is used to parse the JSON file.

Tools: SDL3, Emscripten, C++, CMake, OpenGL ES 2.0, GLM, stb_image, Free Texture Packer, and RapidJSON

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Activating the discrete GeForce of Radeon video card and OpenGL 3.3 Core profile on laptops

You can make it with the following code. The first one is for GeForce. The second one is for Radeon. If you can GeForce the second like with be ignored.

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

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();
}

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

By default the laptops with two video cards use the integrated video card:

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();
}

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

[8Observer8]

Rotate a 3D vector around X, Y, Z axes

In my example, three vectors are rotated 10 degrees around the X, Y and Z axes:

• Rotate the vector (0.f, 0.f, 1.f) 10 degrees around the X axis. Output: (0, -0.173648, 0.984808)
• Rotate the vector (1.f, 0.f, 0.f) 10 degrees around the Y axis. Output: (0.984808, 0, -0.173648)
• Rotate the vector (0.f, 1.f, 0.f) 10 degrees around the Z axis. Output: (-0.173648, 0.984808, 0)

#include <QtGlobal>
#include <QtMath>
#include <QtGui/QOpenGLFunctions>
#include <QtGui/QVector3D>
#include <QtOpenGL/QOpenGLWindow>
#include <QtWidgets/QApplication>

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

        // Rotate a 3D vector around the x-axis
        QVector3D vector1(0.f, 0.f, 1.f);
        QVector3D origin1(0.f, 0.f, 0.f);
        float r1 = qDegreesToRadians(10.f);
        QVector3D out1 = rotateX(vector1, origin1, r1);
        qDebug() << out1;

        // Rotate a 3D vector around the y-axis
        QVector3D vector2(1.f, 0.f, 0.f);
        QVector3D origin2(0.f, 0.f, 0.f);
        float r2 = qDegreesToRadians(10.f);
        QVector3D out2 = rotateY(vector2, origin2, r2);
        qDebug() << out2;

        // Rotate a 3D vector around the z-axis
        QVector3D vector3(0.f, 1.f, 0.f);
        QVector3D origin3(0.f, 0.f, 0.f);
        float r3 = qDegreesToRadians(10.f);
        QVector3D out3 = rotateZ(vector3, origin3, r3);
        qDebug() << out3;
    }

    QVector3D rotateX(const QVector3D &vector, const QVector3D &origin, float rad)
    {
        // Translate point to the origin
        QVector3D pos;
        pos.setX(vector.x() - origin.x());
        pos.setY(vector.y() - origin.y());
        pos.setZ(vector.z() - origin.z());

        // Perform rotation
        QVector3D rot;
        rot.setX(pos.x());
        rot.setY(pos.y() * qCos(rad) - pos.z() * qSin(rad));
        rot.setZ(pos.y() * qSin(rad) + pos.z() * qCos(rad));

        // Translate to correct position
        QVector3D out;
        out.setX(rot.x() + origin.x());
        out.setY(rot.y() + origin.y());
        out.setZ(rot.z() + origin.z());

        return out;
    }

    QVector3D rotateY(const QVector3D &vector, const QVector3D &origin, float rad)
    {
        // Translate point to the origin
        QVector3D pos;
        pos.setX(vector.x() - origin.x());
        pos.setY(vector.y() - origin.y());
        pos.setZ(vector.z() - origin.z());

        // Perform rotation
        QVector3D rot;
        rot.setX(pos.z() * qSin(rad) + pos.x() * qCos(rad));
        rot.setY(pos.y());
        rot.setZ(pos.z() * qCos(rad) - pos.x() * qSin(rad));

        // Translate to correct position
        QVector3D out;
        out.setX(rot.x() + origin.x());
        out.setY(rot.y() + origin.y());
        out.setZ(rot.z() + origin.z());

        return out;
    }

    QVector3D rotateZ(const QVector3D &vector, const QVector3D &origin, float rad)
    {
        // Translate point to the origin
        QVector3D pos;
        pos.setX(vector.x() - origin.x());
        pos.setY(vector.y() - origin.y());
        pos.setZ(vector.z() - origin.z());

        // Perform rotation
        QVector3D rot;
        rot.setX(pos.x() * qCos(rad) - pos.y() * qSin(rad));
        rot.setY(pos.x() * qSin(rad) + pos.y() * qCos(rad));
        rot.setZ(pos.z());

        // Translate to correct position
        QVector3D out;
        out.setX(rot.x() + origin.x());
        out.setY(rot.y() + origin.y());
        out.setZ(rot.z() + origin.z());

        return out;
    }
};

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

pro

QT += core gui openglwidgets

win32: LIBS += -lopengl32

CONFIG += c++17

SOURCES += \
    main.cpp

Source: https://glmatrix.net/docs/vec3.js.html#line564

Using GLM:

// Input vector
auto v = glm::vec3(0.f, 0.f, 1.f);
std::cout << v.x << ", " << v.y << ", " << v.z << std::endl;
// Rotation
auto rotationMatrix = glm::rotate(glm::mat4(1.f), glm::radians(10.f), glm::vec3{1.f, 0.f, 0.f});
auto newVector = rotationMatrix * glm::vec4(v, 0.f);
std::cout << newVector.x << ", " << newVector.y << ", " << newVector.z << std::endl;
// Output: 0, -0.173648, 0.984808

Stack Oveflow: https://stackoverflow.com/a/78633772/4159530

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This post is deleted!

[8Observer8]

I have found two solutions how I can make the first person movement in the browser. Qt doesn't allow it because it is impossible to call emscripten_request_pointerlock() from Qt application: https://bugreports.qt.io/browse/QTBUG-126513

The first solution is to use pure WebGL and Ammo.js: Click to run a demo in the browser

The second solution is to use SDL3, Emscripten, and Bullet Physics: Click to run a demo in the browser

The demo allows to move with first person and third person view:

Baked shadows and textures using SDL3, Emscripten, OpenGL ES 2.0, Bullet Physics, and C++

Demo in the browser

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Critical problems for WebAssembly

• Background color of parent window is changed to black: https://bugreports.qt.io/browse/QTBUG-120651
• emscripten_request_pointerlock() returns EMSCRIPTEN_RESULT_UNKNOWN_TARGET: https://bugreports.qt.io/browse/QTBUG-126513
• Dealing with keyboard layout for input on Qt WebAssembly: https://forum.qt.io/post/790688