qtbase/examples/opengl/qopenglwindow/main.cpp

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#include <QtGui/QOpenGLWindow>
#include <QtGui/QScreen>
#include <QtGui/QPainter>
#include <QtGui/QGuiApplication>
#include <QtGui/QMatrix4x4>
#include <QtGui/QStaticText>

#include "background_renderer.h"

static QPainterPath painterPathForTriangle()
{
    static const QPointF bottomLeft(-1.0, -1.0);
    static const QPointF top(0.0, 1.0);
    static const QPointF bottomRight(1.0, -1.0);

    QPainterPath path(bottomLeft);
    path.lineTo(top);
    path.lineTo(bottomRight);
    path.closeSubpath();
    return path;
}

class OpenGLWindow : public QOpenGLWindow
{
    Q_OBJECT

public:
    // Use NoPartialUpdate. This means that all the rendering goes directly to
    // the window surface, no additional framebuffer object stands in the
    // middle. This is fine since we will clear the entire framebuffer on each
    // paint. Under the hood this means that the behavior is equivalent to the
    // manual makeCurrent - perform OpenGL calls - swapBuffers loop that is
    // typical in pure QWindow-based applications.
    OpenGLWindow()
        : QOpenGLWindow(QOpenGLWindow::NoPartialUpdate)
        , m_fragment_toy("background.frag")
        , m_text_layout("The triangle and this text is rendered with QPainter")
    {
        m_view.lookAt(QVector3D(3,1,1),
                      QVector3D(0,0,0),
                      QVector3D(0,1,0));
        connect(this, SIGNAL(frameSwapped()), this, SLOT(update()));

        QLinearGradient gradient(QPointF(-1,-1), QPointF(1,1));
        gradient.setColorAt(0, Qt::red);
        gradient.setColorAt(1, Qt::green);

        m_brush = QBrush(gradient);
    }

protected:
    void paintGL() Q_DECL_OVERRIDE
    {
        m_fragment_toy.draw(size());

        QPainter p(this);
        p.setWorldTransform(m_window_normalised_matrix.toTransform());

        QMatrix4x4 mvp = m_projection * m_view * m_model_triangle;
        p.setTransform(mvp.toTransform(), true);

        p.fillPath(painterPathForTriangle(), m_brush);

        QTransform text_transform = (m_window_painter_matrix * m_view * m_model_text).toTransform();
        p.setTransform(text_transform, false);
        p.setPen(QPen(Qt::white));
        m_text_layout.prepare(text_transform);
        qreal x = - (m_text_layout.size().width() / 2);
        qreal y = 0;
        p.drawStaticText(x, y, m_text_layout);

        m_model_triangle.rotate(-1, 0, 1, 0);
        m_model_text.rotate(1, 0, 1, 0);
    }

    void resizeGL(int w, int h) Q_DECL_OVERRIDE
    {
        m_window_normalised_matrix.setToIdentity();
        m_window_normalised_matrix.translate(w / 2.0, h / 2.0);
        m_window_normalised_matrix.scale(w / 2.0, -h / 2.0);

        m_window_painter_matrix.setToIdentity();
        m_window_painter_matrix.translate(w / 2.0, h / 2.0);

        m_text_layout.setTextWidth(std::max(w * 0.2, 80.0));

        m_projection.setToIdentity();
        m_projection.perspective(45.f, qreal(w) / qreal(h), 0.1f, 100.f);

    }

private:
    QMatrix4x4 m_window_normalised_matrix;
    QMatrix4x4 m_window_painter_matrix;
    QMatrix4x4 m_projection;
    QMatrix4x4 m_view;
    QMatrix4x4 m_model_triangle;
    QMatrix4x4 m_model_text;
    QBrush m_brush;

    FragmentToy m_fragment_toy;
    QStaticText m_text_layout;
};

int main (int argc, char **argv)
{
    QGuiApplication app(argc, argv);

    OpenGLWindow window;
    QSurfaceFormat fmt;
    fmt.setDepthBufferSize(24);
    fmt.setStencilBufferSize(8);
    window.setFormat(fmt);
    window.show();

    return app.exec();
}

#include "main.moc"