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

        #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, 32);

                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));
        }