Finger Paint Example

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#include <QtWidgets>
#if defined(QT_PRINTSUPPORT_LIB)
#include <QtPrintSupport/qtprintsupportglobal.h>
#if QT_CONFIG(printdialog)
#include <QPrinter>
#include <QPrintDialog>
#endif
#endif

#include "scribblearea.h"

static const qreal MinimumDiameter = 3.0;
static const qreal MaximumDiameter = 50.0;

ScribbleArea::ScribbleArea(QWidget *parent)
    : QWidget(parent)
{
    setAttribute(Qt::WA_AcceptTouchEvents);
    setAttribute(Qt::WA_StaticContents);
    modified = false;

    myPenColors
            << QColor("green")
            << QColor("purple")
            << QColor("red")
            << QColor("blue")
            << QColor("yellow")

            << QColor("pink")
            << QColor("orange")
            << QColor("brown")
            << QColor("grey")
            << QColor("black");
}

bool ScribbleArea::openImage(const QString &fileName)
{
    QImage loadedImage;
    if (!loadedImage.load(fileName))
        return false;

    QSize newSize = loadedImage.size().expandedTo(size());
    resizeImage(&loadedImage, newSize);
    image = loadedImage;
    modified = false;
    update();
    return true;
}

bool ScribbleArea::saveImage(const QString &fileName, const char *fileFormat)
{
    QImage visibleImage = image;
    resizeImage(&visibleImage, size());

    if (visibleImage.save(fileName, fileFormat)) {
        modified = false;
        return true;
    } else {
        return false;
    }
}

void ScribbleArea::clearImage()
{
    image.fill(qRgb(255, 255, 255));
    modified = true;
    update();
}

void ScribbleArea::paintEvent(QPaintEvent *event)
{
    QPainter painter(this);
    const QRect rect = event->rect();
    painter.drawImage(rect.topLeft(), image, rect);
}

void ScribbleArea::resizeEvent(QResizeEvent *event)
{
    if (width() > image.width() || height() > image.height()) {
        int newWidth = qMax(width() + 128, image.width());
        int newHeight = qMax(height() + 128, image.height());
        resizeImage(&image, QSize(newWidth, newHeight));
        update();
    }
    QWidget::resizeEvent(event);
}

void ScribbleArea::resizeImage(QImage *image, const QSize &newSize)
{
    if (image->size() == newSize)
        return;

    QImage newImage(newSize, QImage::Format_RGB32);
    newImage.fill(qRgb(255, 255, 255));
    QPainter painter(&newImage);
    painter.drawImage(QPoint(0, 0), *image);
    *image = newImage;
}

void ScribbleArea::print()
{
#if QT_CONFIG(printdialog)
    QPrinter printer(QPrinter::HighResolution);

    QPrintDialog printDialog(&printer, this);
    if (printDialog.exec() == QDialog::Accepted) {
        QPainter painter(&printer);
        QRect rect = painter.viewport();
        QSize size = image.size();
        size.scale(rect.size(), Qt::KeepAspectRatio);
        painter.setViewport(rect.x(), rect.y(), size.width(), size.height());
        painter.setWindow(image.rect());
        painter.drawImage(0, 0, image);
    }
#endif // QT_CONFIG(printdialog)
}

bool ScribbleArea::event(QEvent *event)
{
    switch (event->type()) {
    case QEvent::TouchBegin:
    case QEvent::TouchUpdate:
    case QEvent::TouchEnd:
    {
        QTouchEvent *touch = static_cast<QTouchEvent *>(event);
        QList<QTouchEvent::TouchPoint> touchPoints = static_cast<QTouchEvent *>(event)->touchPoints();
        foreach (const QTouchEvent::TouchPoint &touchPoint, touchPoints) {
            switch (touchPoint.state()) {
            case Qt::TouchPointStationary:
            case Qt::TouchPointReleased:
                // don't do anything if this touch point hasn't moved or has been released
                continue;
            default:
                {
                    QRectF rect = touchPoint.rect();
                    if (rect.isEmpty()) {
                        qreal diameter = MaximumDiameter;
                        if (touch->device()->capabilities() & QTouchDevice::Pressure)
                            diameter = MinimumDiameter + (MaximumDiameter - MinimumDiameter) * touchPoint.pressure();
                        rect.setSize(QSizeF(diameter, diameter));
                    }

                    QPainter painter(&image);
                    painter.setPen(Qt::NoPen);
                    painter.setBrush(myPenColors.at(touchPoint.id() % myPenColors.count()));
                    painter.drawEllipse(rect);
                    painter.end();

                    modified = true;
                    int rad = 2;
                    update(rect.toRect().adjusted(-rad,-rad, +rad, +rad));
                }
                break;
            }
        }
        break;
    }
    default:
        return QWidget::event(event);
    }
    return true;
}