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# pieview.cpp Example File
itemviews/chart/pieview.cpp

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     #include <math.h>
     #include <QtGui>

     #ifndef M_PI
     #define M_PI 3.1415927
     #endif

     #include "pieview.h"

     PieView::PieView(QWidget *parent)
         : QAbstractItemView(parent)
     {
         horizontalScrollBar()->setRange(0, 0);
         verticalScrollBar()->setRange(0, 0);

         margin = 8;
         totalSize = 300;
         pieSize = totalSize - 2*margin;
         validItems = 0;
         totalValue = 0.0;
         rubberBand = 0;
     }

     void PieView::dataChanged(const QModelIndex &topLeft,
                               const QModelIndex &bottomRight)
     {
         QAbstractItemView::dataChanged(topLeft, bottomRight);

         validItems = 0;
         totalValue = 0.0;

         for (int row = 0; row < model()->rowCount(rootIndex()); ++row) {

             QModelIndex index = model()->index(row, 1, rootIndex());
             double value = model()->data(index).toDouble();

             if (value > 0.0) {
                 totalValue += value;
                 validItems++;
             }
         }
         viewport()->update();
     }

     bool PieView::edit(const QModelIndex &index, EditTrigger trigger, QEvent *event)
     {
         if (index.column() == 0)
             return QAbstractItemView::edit(index, trigger, event);
         else
             return false;
     }

     /*
         Returns the item that covers the coordinate given in the view.
     */

     QModelIndex PieView::indexAt(const QPoint &point) const
     {
         if (validItems == 0)
             return QModelIndex();

         // Transform the view coordinates into contents widget coordinates.
         int wx = point.x() + horizontalScrollBar()->value();
         int wy = point.y() + verticalScrollBar()->value();

         if (wx < totalSize) {
             double cx = wx - totalSize/2;
             double cy = totalSize/2 - wy; // positive cy for items above the center

             // Determine the distance from the center point of the pie chart.
             double d = pow(pow(cx, 2) + pow(cy, 2), 0.5);

             if (d == 0 || d > pieSize/2)
                 return QModelIndex();

             // Determine the angle of the point.
             double angle = (180 / M_PI) * acos(cx/d);
             if (cy < 0)
                 angle = 360 - angle;

             // Find the relevant slice of the pie.
             double startAngle = 0.0;

             for (int row = 0; row < model()->rowCount(rootIndex()); ++row) {

                 QModelIndex index = model()->index(row, 1, rootIndex());
                 double value = model()->data(index).toDouble();

                 if (value > 0.0) {
                     double sliceAngle = 360*value/totalValue;

                     if (angle >= startAngle && angle < (startAngle + sliceAngle))
                         return model()->index(row, 1, rootIndex());

                     startAngle += sliceAngle;
                 }
             }
         } else {
             double itemHeight = QFontMetrics(viewOptions().font).height();
             int listItem = int((wy - margin) / itemHeight);
             int validRow = 0;

             for (int row = 0; row < model()->rowCount(rootIndex()); ++row) {

                 QModelIndex index = model()->index(row, 1, rootIndex());
                 if (model()->data(index).toDouble() > 0.0) {

                     if (listItem == validRow)
                         return model()->index(row, 0, rootIndex());

                     // Update the list index that corresponds to the next valid row.
                     validRow++;
                 }
             }
         }

         return QModelIndex();
     }

     bool PieView::isIndexHidden(const QModelIndex & /*index*/) const
     {
         return false;
     }

     /*
         Returns the rectangle of the item at position \a index in the
         model. The rectangle is in contents coordinates.
     */

     QRect PieView::itemRect(const QModelIndex &index) const
     {
         if (!index.isValid())
             return QRect();

         // Check whether the index's row is in the list of rows represented
         // by slices.
         QModelIndex valueIndex;

         if (index.column() != 1)
             valueIndex = model()->index(index.row(), 1, rootIndex());
         else
             valueIndex = index;

         if (model()->data(valueIndex).toDouble() > 0.0) {

             int listItem = 0;
             for (int row = index.row()-1; row >= 0; --row) {
                 if (model()->data(model()->index(row, 1, rootIndex())).toDouble() > 0.0)
                     listItem++;
             }

             double itemHeight;

             switch (index.column()) {
             case 0:
                 itemHeight = QFontMetrics(viewOptions().font).height();

                 return QRect(totalSize,
                              int(margin + listItem*itemHeight),
                              totalSize - margin, int(itemHeight));
             case 1:
                 return viewport()->rect();
             }

         }
         return QRect();
     }

     QRegion PieView::itemRegion(const QModelIndex &index) const
     {
         if (!index.isValid())
             return QRegion();

         if (index.column() != 1)
             return itemRect(index);

         if (model()->data(index).toDouble() <= 0.0)
             return QRegion();

         double startAngle = 0.0;
         for (int row = 0; row < model()->rowCount(rootIndex()); ++row) {

             QModelIndex sliceIndex = model()->index(row, 1, rootIndex());
             double value = model()->data(sliceIndex).toDouble();

             if (value > 0.0) {
                 double angle = 360*value/totalValue;

                 if (sliceIndex == index) {
                     QPainterPath slicePath;
                     slicePath.moveTo(totalSize/2, totalSize/2);
                     slicePath.arcTo(margin, margin, margin+pieSize, margin+pieSize,
                                     startAngle, angle);
                     slicePath.closeSubpath();

                     return QRegion(slicePath.toFillPolygon().toPolygon());
                 }

                 startAngle += angle;
             }
         }

         return QRegion();
     }

     int PieView::horizontalOffset() const
     {
         return horizontalScrollBar()->value();
     }

     void PieView::mousePressEvent(QMouseEvent *event)
     {
         QAbstractItemView::mousePressEvent(event);
         origin = event->pos();
         if (!rubberBand)
             rubberBand = new QRubberBand(QRubberBand::Rectangle, this);
         rubberBand->setGeometry(QRect(origin, QSize()));
         rubberBand->show();
     }

     void PieView::mouseMoveEvent(QMouseEvent *event)
     {
         if (rubberBand)
             rubberBand->setGeometry(QRect(origin, event->pos()).normalized());
         QAbstractItemView::mouseMoveEvent(event);
     }

     void PieView::mouseReleaseEvent(QMouseEvent *event)
     {
         QAbstractItemView::mouseReleaseEvent(event);
         if (rubberBand)
             rubberBand->hide();
         viewport()->update();
     }

     QModelIndex PieView::moveCursor(QAbstractItemView::CursorAction cursorAction,
                                     Qt::KeyboardModifiers /*modifiers*/)
     {
         QModelIndex current = currentIndex();

         switch (cursorAction) {
             case MoveLeft:
             case MoveUp:
                 if (current.row() > 0)
                     current = model()->index(current.row() - 1, current.column(),
                                              rootIndex());
                 else
                     current = model()->index(0, current.column(), rootIndex());
                 break;
             case MoveRight:
             case MoveDown:
                 if (current.row() < rows(current) - 1)
                     current = model()->index(current.row() + 1, current.column(),
                                              rootIndex());
                 else
                     current = model()->index(rows(current) - 1, current.column(),
                                              rootIndex());
                 break;
             default:
                 break;
         }

         viewport()->update();
         return current;
     }

     void PieView::paintEvent(QPaintEvent *event)
     {
         QItemSelectionModel *selections = selectionModel();
         QStyleOptionViewItem option = viewOptions();
         QStyle::State state = option.state;

         QBrush background = option.palette.base();
         QPen foreground(option.palette.color(QPalette::WindowText));
         QPen textPen(option.palette.color(QPalette::Text));
         QPen highlightedPen(option.palette.color(QPalette::HighlightedText));

         QPainter painter(viewport());
         painter.setRenderHint(QPainter::Antialiasing);

         painter.fillRect(event->rect(), background);
         painter.setPen(foreground);

         // Viewport rectangles
         QRect pieRect = QRect(margin, margin, pieSize, pieSize);
         QPoint keyPoint = QPoint(totalSize - horizontalScrollBar()->value(),
                                  margin - verticalScrollBar()->value());

         if (validItems > 0) {

             painter.save();
             painter.translate(pieRect.x() - horizontalScrollBar()->value(),
                               pieRect.y() - verticalScrollBar()->value());
             painter.drawEllipse(0, 0, pieSize, pieSize);
             double startAngle = 0.0;
             int row;

             for (row = 0; row < model()->rowCount(rootIndex()); ++row) {

                 QModelIndex index = model()->index(row, 1, rootIndex());
                 double value = model()->data(index).toDouble();

                 if (value > 0.0) {
                     double angle = 360*value/totalValue;

                     QModelIndex colorIndex = model()->index(row, 0, rootIndex());
                     QColor color = QColor(model()->data(colorIndex,
                                     Qt::DecorationRole).toString());

                     if (currentIndex() == index)
                         painter.setBrush(QBrush(color, Qt::Dense4Pattern));
                     else if (selections->isSelected(index))
                         painter.setBrush(QBrush(color, Qt::Dense3Pattern));
                     else
                         painter.setBrush(QBrush(color));

                     painter.drawPie(0, 0, pieSize, pieSize, int(startAngle*16),
                                     int(angle*16));

                     startAngle += angle;
                 }
             }
             painter.restore();

             int keyNumber = 0;

             for (row = 0; row < model()->rowCount(rootIndex()); ++row) {

                 QModelIndex index = model()->index(row, 1, rootIndex());
                 double value = model()->data(index).toDouble();

                 if (value > 0.0) {
                     QModelIndex labelIndex = model()->index(row, 0, rootIndex());

                     QStyleOptionViewItem option = viewOptions();
                     option.rect = visualRect(labelIndex);
                     if (selections->isSelected(labelIndex))
                         option.state |= QStyle::State_Selected;
                     if (currentIndex() == labelIndex)
                         option.state |= QStyle::State_HasFocus;
                     itemDelegate()->paint(&painter, option, labelIndex);

                     keyNumber++;
                 }
             }
         }
     }

     void PieView::resizeEvent(QResizeEvent * /* event */)
     {
         updateGeometries();
     }

     int PieView::rows(const QModelIndex &index) const
     {
         return model()->rowCount(model()->parent(index));
     }

     void PieView::rowsInserted(const QModelIndex &parent, int start, int end)
     {
         for (int row = start; row <= end; ++row) {

             QModelIndex index = model()->index(row, 1, rootIndex());
             double value = model()->data(index).toDouble();

             if (value > 0.0) {
                 totalValue += value;
                 validItems++;
             }
         }

         QAbstractItemView::rowsInserted(parent, start, end);
     }

     void PieView::rowsAboutToBeRemoved(const QModelIndex &parent, int start, int end)
     {
         for (int row = start; row <= end; ++row) {

             QModelIndex index = model()->index(row, 1, rootIndex());
             double value = model()->data(index).toDouble();
             if (value > 0.0) {
                 totalValue -= value;
                 validItems--;
             }
         }

         QAbstractItemView::rowsAboutToBeRemoved(parent, start, end);
     }

     void PieView::scrollContentsBy(int dx, int dy)
     {
         viewport()->scroll(dx, dy);
     }

     void PieView::scrollTo(const QModelIndex &index, ScrollHint)
     {
         QRect area = viewport()->rect();
         QRect rect = visualRect(index);

         if (rect.left() < area.left())
             horizontalScrollBar()->setValue(
                 horizontalScrollBar()->value() + rect.left() - area.left());
         else if (rect.right() > area.right())
             horizontalScrollBar()->setValue(
                 horizontalScrollBar()->value() + qMin(
                     rect.right() - area.right(), rect.left() - area.left()));

         if (rect.top() < area.top())
             verticalScrollBar()->setValue(
                 verticalScrollBar()->value() + rect.top() - area.top());
         else if (rect.bottom() > area.bottom())
             verticalScrollBar()->setValue(
                 verticalScrollBar()->value() + qMin(
                     rect.bottom() - area.bottom(), rect.top() - area.top()));

         update();
     }

     /*
         Find the indices corresponding to the extent of the selection.
     */

     void PieView::setSelection(const QRect &rect, QItemSelectionModel::SelectionFlags command)
     {
         // Use content widget coordinates because we will use the itemRegion()
         // function to check for intersections.

         QRect contentsRect = rect.translated(
                                 horizontalScrollBar()->value(),
                                 verticalScrollBar()->value()).normalized();

         int rows = model()->rowCount(rootIndex());
         int columns = model()->columnCount(rootIndex());
         QModelIndexList indexes;

         for (int row = 0; row < rows; ++row) {
             for (int column = 0; column < columns; ++column) {
                 QModelIndex index = model()->index(row, column, rootIndex());
                 QRegion region = itemRegion(index);
                 if (!region.intersect(contentsRect).isEmpty())
                     indexes.append(index);
             }
         }

         if (indexes.size() > 0) {
             int firstRow = indexes[0].row();
             int lastRow = indexes[0].row();
             int firstColumn = indexes[0].column();
             int lastColumn = indexes[0].column();

             for (int i = 1; i < indexes.size(); ++i) {
                 firstRow = qMin(firstRow, indexes[i].row());
                 lastRow = qMax(lastRow, indexes[i].row());
                 firstColumn = qMin(firstColumn, indexes[i].column());
                 lastColumn = qMax(lastColumn, indexes[i].column());
             }

             QItemSelection selection(
                 model()->index(firstRow, firstColumn, rootIndex()),
                 model()->index(lastRow, lastColumn, rootIndex()));
             selectionModel()->select(selection, command);
         } else {
             QModelIndex noIndex;
             QItemSelection selection(noIndex, noIndex);
             selectionModel()->select(selection, command);
         }

         update();
     }

     void PieView::updateGeometries()
     {
         horizontalScrollBar()->setPageStep(viewport()->width());
         horizontalScrollBar()->setRange(0, qMax(0, 2*totalSize - viewport()->width()));
         verticalScrollBar()->setPageStep(viewport()->height());
         verticalScrollBar()->setRange(0, qMax(0, totalSize - viewport()->height()));
     }

     int PieView::verticalOffset() const
     {
         return verticalScrollBar()->value();
     }

     /*
         Returns the position of the item in viewport coordinates.
     */

     QRect PieView::visualRect(const QModelIndex &index) const
     {
         QRect rect = itemRect(index);
         if (rect.isValid())
             return QRect(rect.left() - horizontalScrollBar()->value(),
                          rect.top() - verticalScrollBar()->value(),
                          rect.width(), rect.height());
         else
             return rect;
     }

     /*
         Returns a region corresponding to the selection in viewport coordinates.
     */

     QRegion PieView::visualRegionForSelection(const QItemSelection &selection) const
     {
         int ranges = selection.count();

         if (ranges == 0)
             return QRect();

         QRegion region;
         for (int i = 0; i < ranges; ++i) {
             QItemSelectionRange range = selection.at(i);
             for (int row = range.top(); row <= range.bottom(); ++row) {
                 for (int col = range.left(); col <= range.right(); ++col) {
                     QModelIndex index = model()->index(row, col, rootIndex());
                     region += visualRect(index);
                 }
             }
         }
         return region;
     }