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renderthread.cpp Example File
^{threads/mandelbrot/renderthread.cpp}

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 ** This file is part of the example classes of the Qt Toolkit.
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 ** and appearing in the file LICENSE.GPL included in the packaging of
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 #include <QtGui>

 #include <math.h>

 #include "renderthread.h"

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