Scene Graph - OpenGL Under QML | Qt Quick 5.13.0

Qt 5.13 | Qt Quick | Scene Graph - OpenGL Under QML

Qt 5.13.0 Reference Documentation

# Scene Graph - OpenGL Under QML

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      #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();
      }