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 documentation 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));
    }