简介：界面线程是主线程，工作线程负责绘制图像，然后通过使用信号槽的方式传递给界面线程进行显示。
工作线程与界面线程之间的信号槽

connect(&thread, SIGNAL(renderedImage(QImage,double)), this, SLOT(updatePixmap(QImage,double)));

工作线程重写run函数，实现图像绘制

//! [3]
void RenderThread::run()
{
    forever {
        mutex.lock();
        QSize resultSize = this->resultSize;
        double scaleFactor = this->scaleFactor;
        double centerX = this->centerX;
        double centerY = this->centerY;
        mutex.unlock();
//! [3]

//! [4]
        int halfWidth = resultSize.width() / 2;
//! [4] //! [5]
        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);
//! [5] //! [6]
                ++pass;
            }
//! [6] //! [7]
        }
//! [7]

//! [8]
        mutex.lock();
//! [8] //! [9]
        if (!restart)
            condition.wait(&mutex);
        restart = false;
        mutex.unlock();
    }
}

界面线程重写鼠标移动、鼠标*移动等函数，实现改变绘图焦点

#ifndef QT_NO_WHEELEVENT
//! [12]
void MandelbrotWidget::wheelEvent(QWheelEvent *event)
{
    int numDegrees = event->delta() / 8;
    double numSteps = numDegrees / 15.0f;
    zoom(pow(ZoomInFactor, numSteps));
}
//! [12]
#endif

//! [13]
void MandelbrotWidget::mousePressEvent(QMouseEvent *event)
{
    if (event->button() == Qt::LeftButton)
        lastDragPos = event->pos();
}
//! [13]

//! [14]
void MandelbrotWidget::mouseMoveEvent(QMouseEvent *event)
{
    if (event->buttons() & Qt::LeftButton) {
        pixmapOffset += event->pos() - lastDragPos;
        lastDragPos = event->pos();
        update();
    }
}

通过这个示例，我们知道了在qt中如何添加工作线程，并与界面线程进行交互。使用线程还有一些细节，比如锁还有条件锁。
举例：条件锁
在run函数里condition.wait(&mutex);使程序卡住，然后在render中触发condition.wakeOne();使得程序在卡住的地方继续运行。