/****************************************************************************
**
** Copyright (C) 2012 Nokia Corporation and/or its subsidiary(-ies).
** Contact: http://www.qt-project.org/
**
** This file is part of the demonstration applications of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:LGPL$
** GNU Lesser General Public License Usage
** This file may be used under the terms of the GNU Lesser General Public
** License version 2.1 as published by the Free Software Foundation and
** appearing in the file LICENSE.LGPL included in the packaging of this
** file. Please review the following information to ensure the GNU Lesser
** General Public License version 2.1 requirements will be met:
** http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
**
** In addition, as a special exception, Nokia gives you certain additional
** rights. These rights are described in the Nokia Qt LGPL Exception
** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
**
** GNU General Public License Usage
** Alternatively, this file may be used under the terms of the GNU General
** Public License version 3.0 as published by the Free Software Foundation
** and appearing in the file LICENSE.GPL included in the packaging of this
** file. Please review the following information to ensure the GNU General
** Public License version 3.0 requirements will be met:
** http://www.gnu.org/copyleft/gpl.html.
**
** Other Usage
** Alternatively, this file may be used in accordance with the terms and
** conditions contained in a signed written agreement between you and Nokia.
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** $QT_END_LICENSE$
**
****************************************************************************/

#include "squircle.h"

#include <QtQuick/qsgengine.h>
#include <QtQuick/qquickcanvas.h>
#include <QOpenGLShaderProgram>

Squircle::Squircle()
    : m_program(0)
{
    setFlag(ItemHasContents);
}

void Squircle::itemChange(ItemChange change, const ItemChangeData &)
{
    // The ItemSceneChange event is sent when we are first attached to a canvas.
    if (change == ItemSceneChange) {
        QQuickCanvas *c = canvas();

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

        // If we allow QML to do the clearing, they would clear what we paint
        // and nothing would show.
        c->setClearBeforeRendering(false);
    }
}


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 - 0.3, t + 0.3, i);"
                                           "    gl_FragColor = vec4(coords / 2. + .5, i, i);"
                                           "}");

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

    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);

    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();
}