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# renderthread.cpp Example File
threads/mandelbrot/renderthread.cpp

     /****************************************************************************
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     ** Copyright (C) 2004-2006 Trolltech ASA. All rights reserved.
     **
     ** This file is part of the example classes of the Qt Toolkit.
     **
     ** This file may be used under the terms of the GNU General Public
     ** License version 2.0 as published by the Free Software Foundation
     ** and appearing in the file LICENSE.GPL included in the packaging of
     ** this file.  Please review the following information to ensure GNU
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     ** review the following information:
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     ** WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
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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));
     }