squircle.cpp Example File

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  #include "squircle.h"

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

  Squircle::Squircle()
      : m_t(0)
      , m_renderer(0)
  {
      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 = 0;
      }
  }

  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->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(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();
  }