squircle.cpp Example File

 /****************************************************************************
 **
 ** Copyright (C) 2016 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the demonstration applications of the Qt Toolkit.
 **
 ** $QT_BEGIN_LICENSE:BSD$
 ** Commercial License Usage
 ** Licensees holding valid commercial Qt licenses may use this file in
 ** accordance with the commercial license agreement provided with the
 ** Software or, alternatively, in accordance with the terms contained in
 ** a written agreement between you and The Qt Company. For licensing terms
 ** and conditions see https://www.qt.io/terms-conditions. For further
 ** information use the contact form at https://www.qt.io/contact-us.
 **
 ** BSD License Usage
 ** Alternatively, you may use this file under the terms of the BSD license
 ** as follows:
 **
 ** "Redistribution and use in source and binary forms, with or without
 ** modification, are permitted provided that the following conditions are
 ** met:
 **   * Redistributions of source code must retain the above copyright
 **     notice, this list of conditions and the following disclaimer.
 **   * Redistributions in binary form must reproduce the above copyright
 **     notice, this list of conditions and the following disclaimer in
 **     the documentation and/or other materials provided with the
 **     distribution.
 **   * Neither the name of The Qt Company Ltd nor the names of its
 **     contributors may be used to endorse or promote products derived
 **     from this software without specific prior written permission.
 **
 **
 ** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 ** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 ** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 ** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 ** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 ** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 ** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 ** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 ** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 ** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
 **
 ** $QT_END_LICENSE$
 **
 ****************************************************************************/

 #include "squircle.h"

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

 Squircle::Squircle()
     : m_t(0)
     , m_renderer(nullptr)
 {
     connect(this, &QQuickItem::windowChanged, this, &Squircle::handleWindowChanged);
 }

 void Squircle::setT(qreal t)
 {
     if (t == m_t)
         return;
     m_t = t;
     emit tChanged();
     if (window())
         window()->update();
 }

 void Squircle::handleWindowChanged(QQuickWindow *win)
 {
     if (win) {
         connect(win, &QQuickWindow::beforeSynchronizing, this, &Squircle::sync, Qt::DirectConnection);
         connect(win, &QQuickWindow::sceneGraphInvalidated, this, &Squircle::cleanup, Qt::DirectConnection);
         // If we allow QML to do the clearing, they would clear what we paint
         // and nothing would show.
         win->setClearBeforeRendering(false);
     }
 }

 void Squircle::cleanup()
 {
     if (m_renderer) {
         delete m_renderer;
         m_renderer = nullptr;
     }
 }

 SquircleRenderer::~SquircleRenderer()
 {
     delete m_program;
 }

 void Squircle::sync()
 {
     if (!m_renderer) {
         m_renderer = new SquircleRenderer();
         connect(window(), &QQuickWindow::beforeRendering, m_renderer, &SquircleRenderer::paint, Qt::DirectConnection);
     }
     m_renderer->setViewportSize(window()->size() * window()->devicePixelRatio());
     m_renderer->setT(m_t);
     m_renderer->setWindow(window());
 }

 void SquircleRenderer::paint()
 {
     if (!m_program) {
         initializeOpenGLFunctions();

         m_program = new QOpenGLShaderProgram();
         m_program->addCacheableShaderFromSourceCode(QOpenGLShader::Vertex,
                                                     "attribute highp vec4 vertices;"
                                                     "varying highp vec2 coords;"
                                                     "void main() {"
                                                     "    gl_Position = vertices;"
                                                     "    coords = vertices.xy;"
                                                     "}");
         m_program->addCacheableShaderFromSourceCode(QOpenGLShader::Fragment,
                                                     "uniform lowp float t;"
                                                     "varying highp vec2 coords;"
                                                     "void main() {"
                                                     "    lowp float i = 1. - (pow(abs(coords.x), 4.) + pow(abs(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();

     }
     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, m_viewportSize.width(), m_viewportSize.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();

     // Not strictly needed for this example, but generally useful for when
     // mixing with raw OpenGL.
     m_window->resetOpenGLState();
 }