qtdeclarative/examples/quick/scenegraph/openglunderqml/squircle.cpp

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#include "squircle.h"

#include <QtQuick/qquickwindow.h>
#include <QtGui/QOpenGLShaderProgram>
#include <QtGui/QOpenGLContext>

//! [7]
Squircle::Squircle()
    : m_program(0)
{
}
//! [7]

//! [8]
void Squircle::setT(qreal t)
{
    if (t == m_t)
        return;
    m_t = t;
    emit tChanged();
    if (canvas())
        canvas()->update();
}
//! [8]


//! [1]
void Squircle::itemChange(ItemChange change, const ItemChangeData &)
{
    // The ItemSceneChange event is sent when we are first attached to a window.
    if (change == ItemSceneChange) {
        QQuickWindow *c = window();
        if (!c)
            return;
//! [1]

        // Connect the beforeRendering signal to our paint function.
        // Since this call is executed on the rendering thread it must be
        // a Qt::DirectConnection
//! [2]
        connect(c, SIGNAL(beforeRendering()), this, SLOT(paint()), Qt::DirectConnection);
//! [2]

        // If we allow QML to do the clearing, they would clear what we paint
        // and nothing would show.
//! [3]
        c->setClearBeforeRendering(false);
    }
}
//! [3] //! [4]
void Squircle::paint()
{
    if (!m_program) {
        m_program = new QOpenGLShaderProgram();
        m_program->addShaderFromSourceCode(QOpenGLShader::Vertex,
                                           "attribute highp vec4 vertices;"
                                           "varying highp vec2 coords;"
                                           "void main() {"
                                           "    gl_Position = vertices;"
                                           "    coords = vertices.xy;"
                                           "}");
        m_program->addShaderFromSourceCode(QOpenGLShader::Fragment,
                                           "uniform lowp float t;"
                                           "varying highp vec2 coords;"
                                           "void main() {"
                                           "    lowp float i = 1. - (pow(coords.x, 4.) + pow(coords.y, 4.));"
                                           "    i = smoothstep(t - 0.8, t + 0.8, i);"
                                           "    i = floor(i * 20.) / 20.;"
                                           "    gl_FragColor = vec4(coords * .5 + .5, i, i);"
                                           "}");

        m_program->bindAttributeLocation("vertices", 0);
        m_program->link();

        connect(canvas()->openglContext(), SIGNAL(aboutToBeDestroyed()),
                this, SLOT(cleanup()), Qt::DirectConnection);
    }
//! [4] //! [5]
    m_program->bind();

    m_program->enableAttributeArray(0);

    float values[] = {
        -1, -1,
        1, -1,
        -1, 1,
        1, 1
    };
    m_program->setAttributeArray(0, GL_FLOAT, values, 2);
    m_program->setUniformValue("t", (float) m_t);

    glViewport(0, 0, window()->width(), window()->height());

    glDisable(GL_DEPTH_TEST);

    glClearColor(0, 0, 0, 1);
    glClear(GL_COLOR_BUFFER_BIT);

    glEnable(GL_BLEND);
    glBlendFunc(GL_SRC_ALPHA, GL_ONE);

    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);

    m_program->disableAttributeArray(0);
    m_program->release();
}
//! [5]

//! [6]
void Squircle::cleanup()
{
    if (m_program) {
        delete m_program;
        m_program = 0;
    }
}
//! [6]