Qt 5.11 | Qt Widgets | Tablet Example | tabletcanvas.cpp Example File

Qt 5.11.3 Reference Documentation

# tabletcanvas.cpp Example File

widgets/tablet/tabletcanvas.cpp

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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();
      }