Plug & Paint Basic Tools Example | Qt Widgets 5.13.0

Qt 5.13 | Qt Widgets | Plug & Paint Basic Tools Example

Qt 5.13.0 Reference Documentation

# Plug & Paint Basic Tools Example

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      #include "basictoolsplugin.h"

      #include <QtMath>
      #include <QtWidgets>

      #include <stdlib.h>

      QStringList BasicToolsPlugin::brushes() const
      {
          return {tr("Pencil"), tr("Air Brush"), tr("Random Letters")};
      }

      QRect BasicToolsPlugin::mousePress(const QString &brush, QPainter &painter,
                                         const QPoint &pos)
      {
          return mouseMove(brush, painter, pos, pos);
      }

      QRect BasicToolsPlugin::mouseMove(const QString &brush, QPainter &painter,
                                        const QPoint &oldPos, const QPoint &newPos)
      {
          painter.save();

          int rad = painter.pen().width() / 2;
          QRect boundingRect = QRect(oldPos, newPos).normalized()
                                                    .adjusted(-rad, -rad, +rad, +rad);
          QColor color = painter.pen().color();
          int thickness = painter.pen().width();
          QColor transparentColor(color.red(), color.green(), color.blue(), 0);

          if (brush == tr("Pencil")) {
              painter.drawLine(oldPos, newPos);
          } else if (brush == tr("Air Brush")) {
              int numSteps = 2 + (newPos - oldPos).manhattanLength() / 2;

              painter.setBrush(QBrush(color, Qt::Dense6Pattern));
              painter.setPen(Qt::NoPen);

              for (int i = 0; i < numSteps; ++i) {
                  int x = oldPos.x() + i * (newPos.x() - oldPos.x()) / (numSteps - 1);
                  int y = oldPos.y() + i * (newPos.y() - oldPos.y()) / (numSteps - 1);

                  painter.drawEllipse(x - (thickness / 2), y - (thickness / 2),
                                      thickness, thickness);
              }
          } else if (brush == tr("Random Letters")) {
              QChar ch(QRandomGenerator::global()->bounded('A', 'Z' + 1));

              QFont biggerFont = painter.font();
              biggerFont.setBold(true);
              biggerFont.setPointSize(biggerFont.pointSize() + thickness);
              painter.setFont(biggerFont);

              painter.drawText(newPos, QString(ch));

              QFontMetrics metrics(painter.font());
              boundingRect = metrics.boundingRect(ch);
              boundingRect.translate(newPos);
              boundingRect.adjust(-10, -10, +10, +10);
          }
          painter.restore();
          return boundingRect;
      }

      QRect BasicToolsPlugin::mouseRelease(const QString & /* brush */,
                                           QPainter & /* painter */,
                                           const QPoint & /* pos */)
      {
          return QRect(0, 0, 0, 0);
      }

      QStringList BasicToolsPlugin::shapes() const
      {
          return {tr("Circle"), tr("Star"), tr("Text...")};
      }

      QPainterPath BasicToolsPlugin::generateShape(const QString &shape,
                                                   QWidget *parent)
      {
          QPainterPath path;

          if (shape == tr("Circle")) {
              path.addEllipse(0, 0, 50, 50);
          } else if (shape == tr("Star")) {
              path.moveTo(90, 50);
              for (int i = 1; i < 5; ++i) {
                  path.lineTo(50 + 40 * std::cos(0.8 * i * M_PI),
                              50 + 40 * std::sin(0.8 * i * M_PI));
              }
              path.closeSubpath();
          } else if (shape == tr("Text...")) {
              QString text = QInputDialog::getText(parent, tr("Text Shape"),
                                                   tr("Enter text:"),
                                                   QLineEdit::Normal, tr("Qt"));
              if (!text.isEmpty()) {
                  QFont timesFont("Times", 50);
                  timesFont.setStyleStrategy(QFont::ForceOutline);
                  path.addText(0, 0, timesFont, text);
              }
          }

          return path;
      }

      QStringList BasicToolsPlugin::filters() const
      {
          return {tr("Invert Pixels"), tr("Swap RGB"), tr("Grayscale")};
      }

      QImage BasicToolsPlugin::filterImage(const QString &filter, const QImage &image,
                                           QWidget * /* parent */)
      {
          QImage result = image.convertToFormat(QImage::Format_RGB32);

          if (filter == tr("Invert Pixels")) {
              result.invertPixels();
          } else if (filter == tr("Swap RGB")) {
              result = result.rgbSwapped();
          } else if (filter == tr("Grayscale")) {
              for (int y = 0; y < result.height(); ++y) {
                  for (int x = 0; x < result.width(); ++x) {
                      QRgb pixel = result.pixel(x, y);
                      int gray = qGray(pixel);
                      int alpha = qAlpha(pixel);
                      result.setPixel(x, y, qRgba(gray, gray, gray, alpha));
                  }
              }
          }
          return result;
      }