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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;
        }

        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::mouseReleaseEvent(QMouseEvent *event)
        {
            QAbstractItemView::mouseReleaseEvent(event);
            selectionRect = QRect();
            viewport()->update();
        }

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

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

            viewport()->update();
        }

        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::Foreground));
            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++;
                    }
                }
            }

            if (!selectionRect.isEmpty()) {
                QStyleOptionRubberBand band;
                band.shape = QRubberBand::Rectangle;
                band.rect = selectionRect;
                painter.save();
                style()->drawControl(QStyle::CE_RubberBand, &band, &painter);
                painter.restore();
            }
        }

        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()));
        }

        /*
            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());

            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);
            }

            selectionRect = rect;
            viewport()->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();

            // Note that we use the top and bottom functions of the selection range
            // since the data is stored in rows.

            int firstRow = selection.at(0).top();
            int lastRow = selection.at(0).top();

            for (int i = 0; i < ranges; ++i) {
                firstRow = qMin(firstRow, selection.at(i).top());
                lastRow = qMax(lastRow, selection.at(i).bottom());
            }

            QModelIndex firstItem = model()->index(qMin(firstRow, lastRow), 0, rootIndex());
            QModelIndex lastItem = model()->index(qMax(firstRow, lastRow), 0, rootIndex());

            QRect firstRect = visualRect(firstItem);
            QRect lastRect = visualRect(lastItem);

            return firstRect.unite(lastRect);
        }