tabletcanvas.cpp Example File

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  #include <QtWidgets>
  #include <math.h>

  #include "tabletcanvas.h"

  TabletCanvas::TabletCanvas()
    : QWidget(nullptr)
    , m_alphaChannelValuator(TangentialPressureValuator)
    , m_colorSaturationValuator(NoValuator)
    , m_lineWidthValuator(PressureValuator)
    , m_color(Qt::red)
    , m_brush(m_color)
    , m_pen(m_brush, 1.0, Qt::SolidLine, Qt::RoundCap, Qt::RoundJoin)
    , m_deviceDown(false)
  {
      resize(500, 500);
      setAutoFillBackground(true);
      setAttribute(Qt::WA_TabletTracking);
  }

  bool TabletCanvas::saveImage(const QString &file)
  {
      return m_pixmap.save(file);
  }

  bool TabletCanvas::loadImage(const QString &file)
  {
      bool success = m_pixmap.load(file);

      if (success) {
          update();
          return true;
      }
      return false;
  }

  void TabletCanvas::tabletEvent(QTabletEvent *event)
  {
      switch (event->type()) {
          case QEvent::TabletPress:
              if (!m_deviceDown) {
                  m_deviceDown = true;
                  lastPoint.pos = event->posF();
                  lastPoint.pressure = event->pressure();
                  lastPoint.rotation = event->rotation();
              }
              break;
          case QEvent::TabletMove:
  #ifndef Q_OS_IOS
              if (event->device() == QTabletEvent::RotationStylus)
                  updateCursor(event);
  #endif
              if (m_deviceDown) {
                  updateBrush(event);
                  QPainter painter(&m_pixmap);
                  paintPixmap(painter, event);
                  lastPoint.pos = event->posF();
                  lastPoint.pressure = event->pressure();
                  lastPoint.rotation = event->rotation();
              }
              break;
          case QEvent::TabletRelease:
              if (m_deviceDown && event->buttons() == Qt::NoButton)
                  m_deviceDown = false;
              update();
              break;
          default:
              break;
      }
      event->accept();
  }

  void TabletCanvas::initPixmap()
  {
      qreal dpr = devicePixelRatioF();
      QPixmap newPixmap = QPixmap(width() * dpr, height() * dpr);
      newPixmap.setDevicePixelRatio(dpr);
      newPixmap.fill(Qt::white);
      QPainter painter(&newPixmap);
      if (!m_pixmap.isNull())
          painter.drawPixmap(0, 0, m_pixmap);
      painter.end();
      m_pixmap = newPixmap;
  }

  void TabletCanvas::paintEvent(QPaintEvent *)
  {
      if (m_pixmap.isNull())
          initPixmap();
      QPainter painter(this);
      painter.drawPixmap(0, 0, m_pixmap);
  }

  void TabletCanvas::paintPixmap(QPainter &painter, QTabletEvent *event)
  {
      static qreal maxPenRadius = pressureToWidth(1.0);
      painter.setRenderHint(QPainter::Antialiasing);

      switch (event->device()) {
          case QTabletEvent::Airbrush:
              {
                  painter.setPen(Qt::NoPen);
                  QRadialGradient grad(lastPoint.pos, m_pen.widthF() * 10.0);
                  QColor color = m_brush.color();
                  color.setAlphaF(color.alphaF() * 0.25);
                  grad.setColorAt(0, m_brush.color());
                  grad.setColorAt(0.5, Qt::transparent);
                  painter.setBrush(grad);
                  qreal radius = grad.radius();
                  painter.drawEllipse(event->posF(), radius, radius);
                  update(QRect(event->pos() - QPoint(radius, radius), QSize(radius * 2, radius * 2)));
              }
              break;
          case QTabletEvent::RotationStylus:
              {
                  m_brush.setStyle(Qt::SolidPattern);
                  painter.setPen(Qt::NoPen);
                  painter.setBrush(m_brush);
                  QPolygonF poly;
                  qreal halfWidth = pressureToWidth(lastPoint.pressure);
                  QPointF brushAdjust(qSin(qDegreesToRadians(-lastPoint.rotation)) * halfWidth,
                                      qCos(qDegreesToRadians(-lastPoint.rotation)) * halfWidth);
                  poly << lastPoint.pos + brushAdjust;
                  poly << lastPoint.pos - brushAdjust;
                  halfWidth = m_pen.widthF();
                  brushAdjust = QPointF(qSin(qDegreesToRadians(-event->rotation())) * halfWidth,
                                        qCos(qDegreesToRadians(-event->rotation())) * halfWidth);
                  poly << event->posF() - brushAdjust;
                  poly << event->posF() + brushAdjust;
                  painter.drawConvexPolygon(poly);
                  update(poly.boundingRect().toRect());
              }
              break;
          case QTabletEvent::Puck:
          case QTabletEvent::FourDMouse:
              {
                  const QString error(tr("This input device is not supported by the example."));
  #if QT_CONFIG(statustip)
                  QStatusTipEvent status(error);
                  QApplication::sendEvent(this, &status);
  #else
                  qWarning() << error;
  #endif
              }
              break;
          default:
              {
                  const QString error(tr("Unknown tablet device - treating as stylus"));
  #if QT_CONFIG(statustip)
                  QStatusTipEvent status(error);
                  QApplication::sendEvent(this, &status);
  #else
                  qWarning() << error;
  #endif
              }
              // FALL-THROUGH
          case QTabletEvent::Stylus:
              painter.setPen(m_pen);
              painter.drawLine(lastPoint.pos, event->posF());
              update(QRect(lastPoint.pos.toPoint(), event->pos()).normalized()
                     .adjusted(-maxPenRadius, -maxPenRadius, maxPenRadius, maxPenRadius));
              break;
      }
  }

  qreal TabletCanvas::pressureToWidth(qreal pressure)
  {
      return pressure * 10 + 1;
  }

  void TabletCanvas::updateBrush(const QTabletEvent *event)
  {
      int hue, saturation, value, alpha;
      m_color.getHsv(&hue, &saturation, &value, &alpha);

      int vValue = int(((event->yTilt() + 60.0) / 120.0) * 255);
      int hValue = int(((event->xTilt() + 60.0) / 120.0) * 255);

      switch (m_alphaChannelValuator) {
          case PressureValuator:
              m_color.setAlphaF(event->pressure());
              break;
          case TangentialPressureValuator:
              if (event->device() == QTabletEvent::Airbrush)
                  m_color.setAlphaF(qMax(0.01, (event->tangentialPressure() + 1.0) / 2.0));
              else
                  m_color.setAlpha(255);
              break;
          case TiltValuator:
              m_color.setAlpha(maximum(abs(vValue - 127), abs(hValue - 127)));
              break;
          default:
              m_color.setAlpha(255);
      }

      switch (m_colorSaturationValuator) {
          case VTiltValuator:
              m_color.setHsv(hue, vValue, value, alpha);
              break;
          case HTiltValuator:
              m_color.setHsv(hue, hValue, value, alpha);
              break;
          case PressureValuator:
              m_color.setHsv(hue, int(event->pressure() * 255.0), value, alpha);
              break;
          default:
              ;
      }

      switch (m_lineWidthValuator) {
          case PressureValuator:
              m_pen.setWidthF(pressureToWidth(event->pressure()));
              break;
          case TiltValuator:
              m_pen.setWidthF(maximum(abs(vValue - 127), abs(hValue - 127)) / 12);
              break;
          default:
              m_pen.setWidthF(1);
      }

      if (event->pointerType() == QTabletEvent::Eraser) {
          m_brush.setColor(Qt::white);
          m_pen.setColor(Qt::white);
          m_pen.setWidthF(event->pressure() * 10 + 1);
      } else {
          m_brush.setColor(m_color);
          m_pen.setColor(m_color);
      }
  }

  void TabletCanvas::updateCursor(const QTabletEvent *event)
  {
      QCursor cursor;
      if (event->type() != QEvent::TabletLeaveProximity) {
          if (event->pointerType() == QTabletEvent::Eraser) {
              cursor = QCursor(QPixmap(":/images/cursor-eraser.png"), 3, 28);
          } else {
              switch (event->device()) {
              case QTabletEvent::Stylus:
                  cursor = QCursor(QPixmap(":/images/cursor-pencil.png"), 0, 0);
                  break;
              case QTabletEvent::Airbrush:
                  cursor = QCursor(QPixmap(":/images/cursor-airbrush.png"), 3, 4);
                  break;
              case QTabletEvent::RotationStylus: {
                  QImage origImg(QLatin1String(":/images/cursor-felt-marker.png"));
                  QImage img(32, 32, QImage::Format_ARGB32);
                  QColor solid = m_color;
                  solid.setAlpha(255);
                  img.fill(solid);
                  QPainter painter(&img);
                  QTransform transform = painter.transform();
                  transform.translate(16, 16);
                  transform.rotate(event->rotation());
                  painter.setTransform(transform);
                  painter.setCompositionMode(QPainter::CompositionMode_DestinationIn);
                  painter.drawImage(-24, -24, origImg);
                  painter.setCompositionMode(QPainter::CompositionMode_HardLight);
                  painter.drawImage(-24, -24, origImg);
                  painter.end();
                  cursor = QCursor(QPixmap::fromImage(img), 16, 16);
              } break;
              default:
                  break;
              }
          }
      }
      setCursor(cursor);
  }

  void TabletCanvas::resizeEvent(QResizeEvent *)
  {
      initPixmap();
  }