Qt 5.11 | Qt Core | Mandelbrot Example | renderthread.cpp Example File

Qt 5.11.3 Reference Documentation

# renderthread.cpp Example File

threads/mandelbrot/renderthread.cpp

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      #include "renderthread.h"

      #include <QtWidgets>
      #include <cmath>

      RenderThread::RenderThread(QObject *parent)
          : QThread(parent)
      {
          restart = false;
          abort = false;

          for (int i = 0; i < ColormapSize; ++i)
              colormap[i] = rgbFromWaveLength(380.0 + (i * 400.0 / ColormapSize));
      }

      RenderThread::~RenderThread()
      {
          mutex.lock();
          abort = true;
          condition.wakeOne();
          mutex.unlock();

          wait();
      }

      void RenderThread::render(double centerX, double centerY, double scaleFactor,
                                QSize resultSize)
      {
          QMutexLocker locker(&mutex);

          this->centerX = centerX;
          this->centerY = centerY;
          this->scaleFactor = scaleFactor;
          this->resultSize = resultSize;

          if (!isRunning()) {
              start(LowPriority);
          } else {
              restart = true;
              condition.wakeOne();
          }
      }

      void RenderThread::run()
      {
          forever {
              mutex.lock();
              QSize resultSize = this->resultSize;
              double scaleFactor = this->scaleFactor;
              double centerX = this->centerX;
              double centerY = this->centerY;
              mutex.unlock();

              int halfWidth = resultSize.width() / 2;
              int halfHeight = resultSize.height() / 2;
              QImage image(resultSize, QImage::Format_RGB32);

              const int NumPasses = 8;
              int pass = 0;
              while (pass < NumPasses) {
                  const int MaxIterations = (1 << (2 * pass + 6)) + 32;
                  const int Limit = 4;
                  bool allBlack = true;

                  for (int y = -halfHeight; y < halfHeight; ++y) {
                      if (restart)
                          break;
                      if (abort)
                          return;

                      uint *scanLine =
                              reinterpret_cast<uint *>(image.scanLine(y + halfHeight));
                      double ay = centerY + (y * scaleFactor);

                      for (int x = -halfWidth; x < halfWidth; ++x) {
                          double ax = centerX + (x * scaleFactor);
                          double a1 = ax;
                          double b1 = ay;
                          int numIterations = 0;

                          do {
                              ++numIterations;
                              double a2 = (a1 * a1) - (b1 * b1) + ax;
                              double b2 = (2 * a1 * b1) + ay;
                              if ((a2 * a2) + (b2 * b2) > Limit)
                                  break;

                              ++numIterations;
                              a1 = (a2 * a2) - (b2 * b2) + ax;
                              b1 = (2 * a2 * b2) + ay;
                              if ((a1 * a1) + (b1 * b1) > Limit)
                                  break;
                          } while (numIterations < MaxIterations);

                          if (numIterations < MaxIterations) {
                              *scanLine++ = colormap[numIterations % ColormapSize];
                              allBlack = false;
                          } else {
                              *scanLine++ = qRgb(0, 0, 0);
                          }
                      }
                  }

                  if (allBlack && pass == 0) {
                      pass = 4;
                  } else {
                      if (!restart)
                          emit renderedImage(image, scaleFactor);
                      ++pass;
                  }
              }

              mutex.lock();
              if (!restart)
                  condition.wait(&mutex);
              restart = false;
              mutex.unlock();
          }
      }

      uint RenderThread::rgbFromWaveLength(double wave)
      {
          double r = 0.0;
          double g = 0.0;
          double b = 0.0;

          if (wave >= 380.0 && wave <= 440.0) {
              r = -1.0 * (wave - 440.0) / (440.0 - 380.0);
              b = 1.0;
          } else if (wave >= 440.0 && wave <= 490.0) {
              g = (wave - 440.0) / (490.0 - 440.0);
              b = 1.0;
          } else if (wave >= 490.0 && wave <= 510.0) {
              g = 1.0;
              b = -1.0 * (wave - 510.0) / (510.0 - 490.0);
          } else if (wave >= 510.0 && wave <= 580.0) {
              r = (wave - 510.0) / (580.0 - 510.0);
              g = 1.0;
          } else if (wave >= 580.0 && wave <= 645.0) {
              r = 1.0;
              g = -1.0 * (wave - 645.0) / (645.0 - 580.0);
          } else if (wave >= 645.0 && wave <= 780.0) {
              r = 1.0;
          }

          double s = 1.0;
          if (wave > 700.0)
              s = 0.3 + 0.7 * (780.0 - wave) / (780.0 - 700.0);
          else if (wave <  420.0)
              s = 0.3 + 0.7 * (wave - 380.0) / (420.0 - 380.0);

          r = std::pow(r * s, 0.8);
          g = std::pow(g * s, 0.8);
          b = std::pow(b * s, 0.8);
          return qRgb(int(r * 255), int(g * 255), int(b * 255));
      }