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

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    ** 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 "mandelbrotwidget.h"

    const double DefaultCenterX = -0.637011f;
    const double DefaultCenterY = -0.0395159f;
    const double DefaultScale = 0.00403897f;

    const double ZoomInFactor = 0.8f;
    const double ZoomOutFactor = 1 / ZoomInFactor;
    const int ScrollStep = 20;

    MandelbrotWidget::MandelbrotWidget(QWidget *parent)
        : QWidget(parent)
    {
        centerX = DefaultCenterX;
        centerY = DefaultCenterY;
        pixmapScale = DefaultScale;
        curScale = DefaultScale;

        qRegisterMetaType<QImage>("QImage");
        connect(&thread, SIGNAL(renderedImage(const QImage &, double)),
                this, SLOT(updatePixmap(const QImage &, double)));

        setWindowTitle(tr("Mandelbrot"));
        setCursor(Qt::CrossCursor);
        resize(550, 400);
    }

    void MandelbrotWidget::paintEvent(QPaintEvent * /* event */)
    {
        QPainter painter(this);
        painter.fillRect(rect(), Qt::black);

        if (pixmap.isNull()) {
            painter.setPen(Qt::white);
            painter.drawText(rect(), Qt::AlignCenter,
                             tr("Rendering initial image, please wait..."));
            return;
        }

        if (curScale == pixmapScale) {
            painter.drawPixmap(pixmapOffset, pixmap);
        } else {
            double scaleFactor = pixmapScale / curScale;
            int newWidth = int(pixmap.width() * scaleFactor);
            int newHeight = int(pixmap.height() * scaleFactor);
            int newX = pixmapOffset.x() + (pixmap.width() - newWidth) / 2;
            int newY = pixmapOffset.y() + (pixmap.height() - newHeight) / 2;

            painter.save();
            painter.translate(newX, newY);
            painter.scale(scaleFactor, scaleFactor);
            painter.drawPixmap(0, 0, pixmap);
            painter.restore();
        }

        QString text = tr("Use mouse wheel to zoom. "
                          "Press and hold left mouse button to scroll.");
        QFontMetrics metrics = painter.fontMetrics();
        int textWidth = metrics.width(text);

        painter.setPen(Qt::NoPen);
        painter.setBrush(QColor(0, 0, 0, 127));
        painter.drawRect((width() - textWidth) / 2 - 5, 0, textWidth + 10,
                         metrics.lineSpacing() + 5);
        painter.setPen(Qt::white);
        painter.drawText((width() - textWidth) / 2,
                         metrics.leading() + metrics.ascent(), text);
    }

    void MandelbrotWidget::resizeEvent(QResizeEvent * /* event */)
    {
        thread.render(centerX, centerY, curScale, size());
    }

    void MandelbrotWidget::keyPressEvent(QKeyEvent *event)
    {
        switch (event->key()) {
        case Qt::Key_Plus:
            zoom(ZoomInFactor);
            break;
        case Qt::Key_Minus:
            zoom(ZoomOutFactor);
            break;
        case Qt::Key_Left:
            scroll(-ScrollStep, 0);
            break;
        case Qt::Key_Right:
            scroll(+ScrollStep, 0);
            break;
        case Qt::Key_Down:
            scroll(0, -ScrollStep);
            break;
        case Qt::Key_Up:
            scroll(0, +ScrollStep);
            break;
        default:
            QWidget::keyPressEvent(event);
        }
    }

    void MandelbrotWidget::wheelEvent(QWheelEvent *event)
    {
        int numDegrees = event->delta() / 8;
        double numSteps = numDegrees / 15.0f;
        zoom(pow(ZoomInFactor, numSteps));
    }

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

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

    void MandelbrotWidget::mouseReleaseEvent(QMouseEvent *event)
    {
        if (event->button() == Qt::LeftButton) {
            pixmapOffset += event->pos() - lastDragPos;
            lastDragPos = QPoint();

            int deltaX = (width() - pixmap.width()) / 2 - pixmapOffset.x();
            int deltaY = (height() - pixmap.height()) / 2 - pixmapOffset.y();
            scroll(deltaX, deltaY);
        }
    }

    void MandelbrotWidget::updatePixmap(const QImage &image, double scaleFactor)
    {
        if (!lastDragPos.isNull())
            return;

        pixmap = QPixmap::fromImage(image);
        pixmapOffset = QPoint();
        lastDragPos = QPoint();
        pixmapScale = scaleFactor;
        update();
    }

    void MandelbrotWidget::zoom(double zoomFactor)
    {
        curScale *= zoomFactor;
        update();
        thread.render(centerX, centerY, curScale, size());
    }

    void MandelbrotWidget::scroll(int deltaX, int deltaY)
    {
        centerX += deltaX * curScale;
        centerY += deltaY * curScale;
        update();
        thread.render(centerX, centerY, curScale, size());
    }