KChart/Polar/KChartPieDiagram.cpp

/*
 * Copyright (C) 2001-2015 Klaralvdalens Datakonsult AB.  All rights reserved.
 *
 * This file is part of the KD Chart library.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 of
 * the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

#include "KChartPieDiagram.h"
#include "KChartPieDiagram_p.h"

#include "KChartPaintContext.h"
#include "KChartPieAttributes.h"
#include "KChartPolarCoordinatePlane_p.h"
#include "KChartThreeDPieAttributes.h"
#include "KChartPainterSaver_p.h"
#include "KChartMath_p.h"

#include <QDebug>
#include <QPainter>
#include <QStack>


using namespace KChart;

PieDiagram::Private::Private()
  : labelDecorations( PieDiagram::NoDecoration ),
    isCollisionAvoidanceEnabled( false )
{
}

PieDiagram::Private::~Private() {}

#define d d_func()

PieDiagram::PieDiagram( QWidget* parent, PolarCoordinatePlane* plane ) :
    AbstractPieDiagram( new Private(), parent, plane )
{
    init();
}

PieDiagram::~PieDiagram()
{
}

void PieDiagram::init()
{
}

PieDiagram * PieDiagram::clone() const
{
    return new PieDiagram( new Private( *d ) );
}

void PieDiagram::setLabelDecorations( LabelDecorations decorations )
{
    d->labelDecorations = decorations;
}

PieDiagram::LabelDecorations PieDiagram::labelDecorations() const
{
    return d->labelDecorations;
}

void PieDiagram::setLabelCollisionAvoidanceEnabled( bool enabled )
{
    d->isCollisionAvoidanceEnabled = enabled;
}

bool PieDiagram::isLabelCollisionAvoidanceEnabled() const
{
    return d->isCollisionAvoidanceEnabled;
}

const QPair<QPointF, QPointF> PieDiagram::calculateDataBoundaries () const
{
    if ( !checkInvariants( true ) || model()->rowCount() < 1 ) return QPair<QPointF, QPointF>( QPointF( 0, 0 ), QPointF( 0, 0 ) );

    const PieAttributes attrs( pieAttributes() );

    QPointF bottomLeft( QPointF( 0, 0 ) );
    QPointF topRight;
    // If we explode, we need extra space for the slice that has the largest explosion distance.
    if ( attrs.explode() ) {
        const int colCount = columnCount();
        qreal maxExplode = 0.0;
        for ( int j = 0; j < colCount; ++j ) {
            const PieAttributes columnAttrs( pieAttributes( model()->index( 0, j, rootIndex() ) ) ); // checked
            maxExplode = qMax( maxExplode, columnAttrs.explodeFactor() );
        }
        topRight = QPointF( 1.0 + maxExplode, 1.0 + maxExplode );
    } else {
        topRight = QPointF( 1.0, 1.0 );
    }
    return QPair<QPointF, QPointF> ( bottomLeft,  topRight );
}


void PieDiagram::paintEvent( QPaintEvent* )
{
    QPainter painter ( viewport() );
    PaintContext ctx;
    ctx.setPainter ( &painter );
    ctx.setRectangle( QRectF ( 0, 0, width(), height() ) );
    paint ( &ctx );
}

void PieDiagram::resizeEvent( QResizeEvent* )
{
}

void PieDiagram::resize( const QSizeF& size )
{
    AbstractPieDiagram::resize(size);
}

void PieDiagram::paint( PaintContext* ctx )
{
    // Painting is a two stage process
    // In the first stage we figure out how much space is needed
    // for text labels.
    // In the second stage, we make use of that information and
    // perform the actual painting.
    placeLabels( ctx );
    paintInternal( ctx );
}

void PieDiagram::calcSliceAngles()
{
    // determine slice positions and sizes
    const qreal sum = valueTotals();
    const qreal sectorsPerValue = 360.0 / sum;
    const PolarCoordinatePlane* plane = polarCoordinatePlane();
    qreal currentValue = plane ? plane->startPosition() : 0.0;

    const int colCount = columnCount();
    d->startAngles.resize( colCount );
    d->angleLens.resize( colCount );

    bool atLeastOneValue = false; // guard against completely empty tables
    for ( int iColumn = 0; iColumn < colCount; ++iColumn ) {
        bool isOk;
        const qreal cellValue = qAbs( model()->data( model()->index( 0, iColumn, rootIndex() ) ) // checked
            .toReal( &isOk ) );
        // toReal() returns 0.0 if there was no value or a non-numeric value
        atLeastOneValue = atLeastOneValue || isOk;

        d->startAngles[ iColumn ] = currentValue;
        d->angleLens[ iColumn ] = cellValue * sectorsPerValue;

        currentValue = d->startAngles[ iColumn ] + d->angleLens[ iColumn ];
    }

    // If there was no value at all, this is the sign for other code to bail out
    if ( !atLeastOneValue ) {
        d->startAngles.clear();
        d->angleLens.clear();
    }
}

void PieDiagram::calcPieSize( const QRectF &contentsRect )
{
    d->size = qMin( contentsRect.width(), contentsRect.height() );

    // if any slice explodes, the whole pie needs additional space so we make the basic size smaller
    qreal maxExplode = 0.0;
    const int colCount = columnCount();
    for ( int j = 0; j < colCount; ++j ) {
        const PieAttributes columnAttrs( pieAttributes( model()->index( 0, j, rootIndex() ) ) ); // checked
        maxExplode = qMax( maxExplode, columnAttrs.explodeFactor() );
    }
    d->size /= ( 1.0 + 1.0 * maxExplode );

    if ( d->size < 0.0 ) {
        d->size = 0;
    }
}

// this is the rect of the top surface of the pie, i.e. excluding the "3D" rim effect.
QRectF PieDiagram::twoDPieRect( const QRectF &contentsRect, const ThreeDPieAttributes& threeDAttrs ) const
{
    QRectF pieRect;
    if ( !threeDAttrs.isEnabled() ) {
        qreal x = ( contentsRect.width() - d->size ) / 2.0;
        qreal y = ( contentsRect.height() - d->size ) / 2.0;
        pieRect = QRectF( contentsRect.left() + x, contentsRect.top() + y, d->size, d->size );
    } else {
        // threeD: width is the maximum possible width; height is 1/2 of that
        qreal sizeFor3DEffect = 0.0;

        qreal x = ( contentsRect.width() - d->size ) / 2.0;
        qreal height = d->size;
        // make sure that the height plus the threeDheight is not more than the
        // available size
        if ( threeDAttrs.depth() >= 0.0 ) {
            // positive pie height: absolute value
            sizeFor3DEffect = threeDAttrs.depth();
            height = d->size - sizeFor3DEffect;
        } else {
            // negative pie height: relative value
            sizeFor3DEffect = - threeDAttrs.depth() / 100.0 * height;
            height = d->size - sizeFor3DEffect;
        }
        qreal y = ( contentsRect.height() - height - sizeFor3DEffect ) / 2.0;

        pieRect = QRectF( contentsRect.left() + x, contentsRect.top() + y, d->size, height );
    }
    return pieRect;
}

void PieDiagram::placeLabels( PaintContext* paintContext )
{
    if ( !checkInvariants(true) || model()->rowCount() < 1 ) {
        return;
    }
    if ( paintContext->rectangle().isEmpty() || valueTotals() == 0.0 ) {
        return;
    }

    const ThreeDPieAttributes threeDAttrs( threeDPieAttributes() );
    const int colCount = columnCount();

    d->reverseMapper.clear(); // on first call, this sets up the internals of the ReverseMapper.

    calcSliceAngles();
    if ( d->startAngles.isEmpty() ) {
        return;
    }

    calcPieSize( paintContext->rectangle() );

    // keep resizing the pie until the labels and the pie fit into paintContext->rectangle()

    bool tryAgain = true;
    while ( tryAgain ) {
        tryAgain = false;

        QRectF pieRect = twoDPieRect( paintContext->rectangle(), threeDAttrs );
        d->forgetAlreadyPaintedDataValues();
        d->labelPaintCache.clear();

        for ( int slice = 0; slice < colCount; slice++ ) {
            if ( d->angleLens[ slice ] != 0.0 ) {
                const QRectF explodedPieRect = explodedDrawPosition( pieRect, slice );
                addSliceLabel( &d->labelPaintCache, explodedPieRect, slice );
            }
        }

        QRectF textBoundingRect;
        d->paintDataValueTextsAndMarkers( paintContext, d->labelPaintCache, false, true,
                                          &textBoundingRect );
        if ( d->isCollisionAvoidanceEnabled ) {
            shuffleLabels( &textBoundingRect );
        }

        if ( !textBoundingRect.isEmpty() && d->size > 0.0 ) {
            const QRectF &clipRect = paintContext->rectangle();
            // see by how many pixels the text is clipped on each side
            qreal right = qMax( qreal( 0.0 ), textBoundingRect.right() - clipRect.right() );
            qreal left = qMax( qreal( 0.0 ), clipRect.left() - textBoundingRect.left() );
            // attention here - y coordinates in Qt are inverted compared to the convention in maths
            qreal top = qMax( qreal( 0.0 ), clipRect.top() - textBoundingRect.top() );
            qreal bottom = qMax( qreal( 0.0 ), textBoundingRect.bottom() - clipRect.bottom() );
            qreal maxOverhang = qMax( qMax( right, left ), qMax( top, bottom ) );

            if ( maxOverhang > 0.0 ) {
                // subtract 2x as much because every side only gets half of the total diameter reduction
                // and we have to make up for the overhang on one particular side.
                d->size -= qMin<qreal>( d->size, maxOverhang * 2.0 );
                tryAgain = true;
            }
        }
    }
}

static int wraparound( int i, int size )
{
    while ( i < 0 ) {
        i += size;
    }
    while ( i >= size ) {
        i -= size;
    }
    return i;
}

//#define SHUFFLE_DEBUG

void PieDiagram::shuffleLabels( QRectF* textBoundingRect )
{
    // things that could be improved here:
    // - use a variable number (chosen using angle information) of neighbors to check
    // - try harder to arrange the labels to look nice

    // ideas:
    // - leave labels that don't collide alone (only if they their offset is zero)
    // - use a graphics view for collision detection

    LabelPaintCache& lpc = d->labelPaintCache;
    const int n = lpc.paintReplay.size();
    bool modified = false;
    qreal direction = 5.0;
    QVector< qreal > offsets;
    offsets.fill( 0.0, n );

    for ( bool lastRoundModified = true; lastRoundModified; ) {
        lastRoundModified = false;

        for ( int i = 0; i < n; i++ ) {
            const int neighborsToCheck = qMax( 10, lpc.paintReplay.size() - 1 );
            const int minComp = wraparound( i - neighborsToCheck / 2, n );
            const int maxComp = wraparound( i + ( neighborsToCheck + 1 ) / 2, n );

            QPainterPath& path = lpc.paintReplay[ i ].labelArea;

            for ( int j = minComp; j != maxComp; j = wraparound( j + 1, n ) ) {
                if ( i == j ) {
                    continue;
                }
                QPainterPath& otherPath = lpc.paintReplay[ j ].labelArea;

                while ( ( offsets[ i ] + direction > 0 ) && otherPath.intersects( path ) ) {
#ifdef SHUFFLE_DEBUG
                    qDebug() << "collision involving" << j << "and" << i << " -- n =" << n;
                    TextAttributes ta = lpc.paintReplay[ i ].attrs.textAttributes();
                    ta.setPen( QPen( Qt::white ) );
                    lpc.paintReplay[ i ].attrs.setTextAttributes( ta );
#endif
                    uint slice = lpc.paintReplay[ i ].index.column();
                    qreal angle = DEGTORAD( d->startAngles[ slice ] + d->angleLens[ slice ] / 2.0 );
                    qreal dx = cos( angle ) * direction;
                    qreal dy = -sin( angle ) * direction;
                    offsets[ i ] += direction;
                    path.translate( dx, dy );
                    lastRoundModified = true;
                }
            }
        }
        direction *= -1.07; // this can "overshoot", but avoids getting trapped in local minimums
        modified = modified || lastRoundModified;
    }

    if ( modified ) {
        for ( int i = 0; i < lpc.paintReplay.size(); i++ ) {
            *textBoundingRect |= lpc.paintReplay[ i ].labelArea.boundingRect();
        }
    }
}

static QPolygonF polygonFromPainterPath( const QPainterPath &pp )
{
    QPolygonF ret;
    for ( int i = 0; i < pp.elementCount(); i++ ) {
        const QPainterPath::Element& el = pp.elementAt( i );
        Q_ASSERT( el.type == QPainterPath::MoveToElement || el.type == QPainterPath::LineToElement );
        ret.append( el );
    }
    return ret;
}

// you can call it "normalizedProjectionLength" if you like
static qreal normProjection( const QLineF &l1, const QLineF &l2 )
{
    const qreal dotProduct = l1.dx() * l2.dx() + l1.dy() * l2.dy();
    return qAbs( dotProduct / ( l1.length() * l2.length() ) );
}

static QLineF labelAttachmentLine( const QPointF &center, const QPointF &start, const QPainterPath &label )
{
    Q_ASSERT ( label.elementCount() == 5 );

    // start is assumed to lie on the outer rim of the slice(!), making it possible to derive the
    // radius of the pie
    const qreal pieRadius = QLineF( center, start ).length();

    // don't draw a line at all when the label is connected to its slice due to at least one of its
    // corners falling inside the slice.
    for ( int i = 0; i < 4; i++ ) { // point 4 is just a duplicate of point 0
        if ( QLineF( label.elementAt( i ), center ).length() < pieRadius ) {
            return QLineF();
        }
    }

    // find the closest edge in the polygon, and its two neighbors
    QPointF closeCorners[3];
    {
        QPointF closest = QPointF( 1000000, 1000000 );
        int closestIndex = 0; // better misbehave than crash
        for ( int i = 0; i < 4; i++ ) { // point 4 is just a duplicate of point 0
            QPointF p = label.elementAt( i );
            if ( QLineF( p, center ).length() < QLineF( closest, center ).length() ) {
                closest = p;
                closestIndex = i;
            }
        }

        closeCorners[ 0 ] = label.elementAt( wraparound( closestIndex - 1, 4 ) );
        closeCorners[ 1 ] = closest;
        closeCorners[ 2 ] = label.elementAt( wraparound( closestIndex + 1, 4 ) );
    }

    QLineF edge1 = QLineF( closeCorners[ 0 ], closeCorners[ 1 ] );
    QLineF edge2 = QLineF( closeCorners[ 1 ], closeCorners[ 2 ] );
    QLineF connection1 = QLineF( ( closeCorners[ 0 ] + closeCorners[ 1 ] ) / 2.0, center );
    QLineF connection2 = QLineF( ( closeCorners[ 1 ] + closeCorners[ 2 ] ) / 2.0, center );
    QLineF ret;
    // prefer the connecting line meeting its edge at a more perpendicular angle
    if ( normProjection( edge1, connection1 ) < normProjection( edge2, connection2 ) ) {
        ret = connection1;
    } else {
        ret = connection2;
    }

    // This tends to look a bit better than not doing it *shrug*
    ret.setP2( ( start + center ) / 2.0 );

    // make the line end at the rim of the slice (not 100% accurate because the line is not precisely radial)
    qreal p1Radius = QLineF( ret.p1(), center ).length();
    ret.setLength( p1Radius - pieRadius );

    return ret;
}

void PieDiagram::paintInternal( PaintContext* paintContext )
{
    // note: Not having any data model assigned is no bug
    //       but we can not draw a diagram then either.
    if ( !checkInvariants( true ) || model()->rowCount() < 1 ) {
        return;
    }
    if ( d->startAngles.isEmpty() || paintContext->rectangle().isEmpty() || valueTotals() == 0.0 ) {
        return;
    }

    const ThreeDPieAttributes threeDAttrs( threeDPieAttributes() );
    const int colCount = columnCount();

    // Paint from back to front ("painter's algorithm") - first draw the backmost slice,
    // then the slices on the left and right from back to front, then the frontmost one.

    QRectF pieRect = twoDPieRect( paintContext->rectangle(), threeDAttrs );
    const int backmostSlice = findSliceAt( 90, colCount );
    const int frontmostSlice = findSliceAt( 270, colCount );
    int currentLeftSlice = backmostSlice;
    int currentRightSlice = backmostSlice;

    drawSlice( paintContext->painter(), pieRect, backmostSlice );

    if ( backmostSlice == frontmostSlice ) {
        const int rightmostSlice = findSliceAt( 0, colCount );
        const int leftmostSlice = findSliceAt( 180, colCount );

        if ( backmostSlice == leftmostSlice ) {
            currentLeftSlice = findLeftSlice( currentLeftSlice, colCount );
        }
        if ( backmostSlice == rightmostSlice ) {
            currentRightSlice = findRightSlice( currentRightSlice, colCount );
        }
    }

    while ( currentLeftSlice != frontmostSlice ) {
        if ( currentLeftSlice != backmostSlice ) {
            drawSlice( paintContext->painter(), pieRect, currentLeftSlice );
        }
        currentLeftSlice = findLeftSlice( currentLeftSlice, colCount );
    }

    while ( currentRightSlice != frontmostSlice ) {
        if ( currentRightSlice != backmostSlice ) {
            drawSlice( paintContext->painter(), pieRect, currentRightSlice );
        }
        currentRightSlice = findRightSlice( currentRightSlice, colCount );
    }

    // if the backmost slice is not the frontmost slice, we draw the frontmost one last
    if ( backmostSlice != frontmostSlice || ! threeDPieAttributes().isEnabled() ) {
        drawSlice( paintContext->painter(), pieRect, frontmostSlice );
    }

    d->paintDataValueTextsAndMarkers( paintContext, d->labelPaintCache, false, false );
    // it's safer to do this at the beginning of placeLabels, but we can save some memory here.
    d->forgetAlreadyPaintedDataValues();
    // ### maybe move this into AbstractDiagram, also make ReverseMapper deal better with multiple polygons
    const QPointF center = paintContext->rectangle().center();
    const PainterSaver painterSaver( paintContext->painter() );
    paintContext->painter()->setBrush( Qt::NoBrush );
    Q_FOREACH( const LabelPaintInfo &pi, d->labelPaintCache.paintReplay ) {
        // we expect the PainterPath to be a rectangle
        if ( pi.labelArea.elementCount() != 5 ) {
            continue;
        }

        paintContext->painter()->setPen( pen( pi.index ) );
        if ( d->labelDecorations & LineFromSliceDecoration ) {
            paintContext->painter()->drawLine( labelAttachmentLine( center, pi.markerPos, pi.labelArea ) );
        }
        if ( d->labelDecorations & FrameDecoration ) {
            paintContext->painter()->drawPath( pi.labelArea );
        }
        d->reverseMapper.addPolygon( pi.index.row(), pi.index.column(),
                                     polygonFromPainterPath( pi.labelArea ) );
    }
    d->labelPaintCache.clear();
    d->startAngles.clear();
    d->angleLens.clear();
}

#if defined ( Q_OS_WIN)
#define trunc(x) ((int)(x))
#endif

QRectF PieDiagram::explodedDrawPosition( const QRectF& drawPosition, uint slice ) const
{
    const QModelIndex index( model()->index( 0, slice, rootIndex() ) ); // checked
    const PieAttributes attrs( pieAttributes( index ) );

    QRectF adjustedDrawPosition = drawPosition;
    if ( attrs.explode() ) {
        qreal startAngle = d->startAngles[ slice ];
        qreal angleLen = d->angleLens[ slice ];
        qreal explodeAngle = ( DEGTORAD( startAngle + angleLen / 2.0 ) );
        qreal explodeDistance = attrs.explodeFactor() * d->size / 2.0;

        adjustedDrawPosition.translate( explodeDistance * cos( explodeAngle ),
                                        explodeDistance * - sin( explodeAngle ) );
    }
    return adjustedDrawPosition;
}

void PieDiagram::drawSlice( QPainter* painter, const QRectF& drawPosition, uint slice)
{
    // Is there anything to draw at all?
    if ( d->angleLens[ slice ] == 0.0 ) {
        return;
    }
    const QRectF adjustedDrawPosition = explodedDrawPosition( drawPosition, slice );
    draw3DEffect( painter, adjustedDrawPosition, slice );
    drawSliceSurface( painter, adjustedDrawPosition, slice );
}

void PieDiagram::drawSliceSurface( QPainter* painter, const QRectF& drawPosition, uint slice )
{
    // Is there anything to draw at all?
    const qreal angleLen = d->angleLens[ slice ];
    const qreal startAngle = d->startAngles[ slice ];
    const QModelIndex index( model()->index( 0, slice, rootIndex() ) ); // checked

    const PieAttributes attrs( pieAttributes( index ) );
    const ThreeDPieAttributes threeDAttrs( threeDPieAttributes( index ) );

    painter->setRenderHint ( QPainter::Antialiasing );
    QBrush br = brush( index );
    if ( threeDAttrs.isEnabled() ) {
        br = threeDAttrs.threeDBrush( br, drawPosition );
    }
    painter->setBrush( br );

    QPen pen = this->pen( index );
    if ( threeDAttrs.isEnabled() ) {
        pen.setColor( Qt::black );
    }
    painter->setPen( pen );

    if ( angleLen == 360 ) {
        // full circle, avoid nasty line in the middle
        painter->drawEllipse( drawPosition );

        //Add polygon to Reverse mapper for showing tool tips.
        QPolygonF poly( drawPosition );
        d->reverseMapper.addPolygon( index.row(), index.column(), poly );
    } else {
        // draw the top of this piece
        // Start with getting the points for the arc.
        const int arcPoints = static_cast<int>(trunc( angleLen / granularity() ));
        QPolygonF poly( arcPoints + 2 );
        qreal degree = 0.0;
        int iPoint = 0;
        bool perfectMatch = false;

        while ( degree <= angleLen ) {
            poly[ iPoint ] = pointOnEllipse( drawPosition, startAngle + degree );
            //qDebug() << degree << angleLen << poly[ iPoint ];
            perfectMatch = ( degree == angleLen );
            degree += granularity();
            ++iPoint;
        }
        // if necessary add one more point to fill the last small gap
        if ( !perfectMatch ) {
            poly[ iPoint ] = pointOnEllipse( drawPosition, startAngle + angleLen );

            // add the center point of the piece
            poly.append( drawPosition.center() );
        } else {
            poly[ iPoint ] = drawPosition.center();
        }
        //find the value and paint it
        //fix value position
        d->reverseMapper.addPolygon( index.row(), index.column(), poly );

        painter->drawPolygon( poly );
    }
}

// calculate the position points for the label and pass them to addLabel()
void PieDiagram::addSliceLabel( LabelPaintCache* lpc, const QRectF& drawPosition, uint slice )
{
    const qreal angleLen = d->angleLens[ slice ];
    const qreal startAngle = d->startAngles[ slice ];
    const QModelIndex index( model()->index( 0, slice, rootIndex() ) ); // checked
    const qreal sum = valueTotals();

    // Position points are calculated relative to the slice.
    // They are calculated as if the slice was 'standing' on its tip and the rim was up,
    // so North is the middle (also highest part) of the rim and South is the tip of the slice.

    const QPointF south = drawPosition.center();
    const QPointF southEast = south;
    const QPointF southWest = south;
    const QPointF north = pointOnEllipse( drawPosition, startAngle + angleLen / 2.0 );

    const QPointF northEast = pointOnEllipse( drawPosition, startAngle );
    const QPointF northWest = pointOnEllipse( drawPosition, startAngle + angleLen );
    QPointF center = ( south + north ) / 2.0;
    const QPointF east = ( south + northEast ) / 2.0;
    const QPointF west = ( south + northWest ) / 2.0;

    PositionPoints points( center, northWest, north, northEast, east, southEast, south, southWest, west );
    qreal topAngle = startAngle - 90;
    if ( topAngle < 0.0 ) {
        topAngle += 360.0;
    }

    points.setDegrees( KChartEnums::PositionEast, topAngle );
    points.setDegrees( KChartEnums::PositionNorthEast, topAngle );
    points.setDegrees( KChartEnums::PositionWest, topAngle + angleLen );
    points.setDegrees( KChartEnums::PositionNorthWest, topAngle + angleLen );
    points.setDegrees( KChartEnums::PositionCenter, topAngle + angleLen / 2.0 );
    points.setDegrees( KChartEnums::PositionNorth, topAngle + angleLen / 2.0 );

    qreal favoriteTextAngle = 0.0;
    if ( autoRotateLabels() ) {
        favoriteTextAngle = - ( startAngle + angleLen / 2 ) + 90.0;
        while ( favoriteTextAngle <= 0.0 ) {
            favoriteTextAngle += 360.0;
        }
        // flip the label when upside down
        if ( favoriteTextAngle > 90.0 && favoriteTextAngle < 270.0 ) {
            favoriteTextAngle = favoriteTextAngle - 180.0;
        }
        // negative angles can have special meaning in addLabel; otherwise they work fine
        if ( favoriteTextAngle <= 0.0 ) {
            favoriteTextAngle += 360.0;
        }
    }

    d->addLabel( lpc, index, nullptr, points, Position::Center, Position::Center,
                 angleLen * sum / 360, favoriteTextAngle );
}

static bool doSpansOverlap( qreal s1Start, qreal s1End, qreal s2Start, qreal s2End )
{
    if ( s1Start < s2Start ) {
        return s1End >= s2Start;
    } else {
        return s1Start <= s2End;
    }
}

static bool doArcsOverlap( qreal a1Start, qreal a1End, qreal a2Start, qreal a2End )
{
    Q_ASSERT( a1Start >= 0 && a1Start <= 360 && a1End >= 0 && a1End <= 360 &&
              a2Start >= 0 && a2Start <= 360 && a2End >= 0 && a2End <= 360 );
    // all of this could probably be done better...
    if ( a1End < a1Start ) {
        a1End += 360;
    }
    if ( a2End < a2Start ) {
        a2End += 360;
    }

    if ( doSpansOverlap( a1Start, a1End, a2Start, a2End ) ) {
        return true;
    }
    if ( a1Start > a2Start ) {
        return doSpansOverlap( a1Start - 360.0, a1End - 360.0, a2Start, a2End );
    } else {
        return doSpansOverlap( a1Start + 360.0, a1End + 360.0, a2Start, a2End );
    }
}

void PieDiagram::draw3DEffect( QPainter* painter, const QRectF& drawPosition, uint slice )
{
    const QModelIndex index( model()->index( 0, slice, rootIndex() ) ); // checked
    const ThreeDPieAttributes threeDAttrs( threeDPieAttributes( index ) );
    if ( ! threeDAttrs.isEnabled() ) {
        return;
    }

    // NOTE: We cannot optimize away drawing some of the effects (even
    // when not exploding), because some of the pies might be left out
    // in future versions which would make some of the normally hidden
    // pies visible. Complex hidden-line algorithms would be much more
    // expensive than just drawing for nothing.

    // No need to save the brush, will be changed on return from this
    // method anyway.
    const QBrush brush = this->brush( model()->index( 0, slice, rootIndex() ) ); // checked
    if ( threeDAttrs.useShadowColors() ) {
        painter->setBrush( QBrush( brush.color().darker() ) );
    } else {
        painter->setBrush( brush );
    }

    qreal startAngle = d->startAngles[ slice ];
    qreal endAngle = startAngle + d->angleLens[ slice ];
    // Normalize angles
    while ( startAngle >= 360 )
        startAngle -= 360;
    while ( endAngle >= 360 )
        endAngle -= 360;
    Q_ASSERT( startAngle >= 0 && startAngle <= 360 );
    Q_ASSERT( endAngle >= 0 && endAngle <= 360 );

    // positive pie height: absolute value
    // negative pie height: relative value
    const int depth = threeDAttrs.depth() >= 0.0 ? threeDAttrs.depth() : -threeDAttrs.depth() / 100.0 * drawPosition.height();

    if ( startAngle == endAngle || startAngle == endAngle - 360 ) { // full circle
        draw3dOuterRim( painter, drawPosition, depth, 180, 360 );
    } else {
        if ( doArcsOverlap( startAngle, endAngle, 180, 360 ) ) {
            draw3dOuterRim( painter, drawPosition, depth, startAngle, endAngle );
        }

        if ( startAngle >= 270 || startAngle <= 90 ) {
            draw3dCutSurface( painter, drawPosition, depth, startAngle );
        }
        if ( endAngle >= 90 && endAngle <= 270 ) {
            draw3dCutSurface( painter, drawPosition, depth, endAngle );
        }
    }
}


void PieDiagram::draw3dCutSurface( QPainter* painter,
        const QRectF& rect,
        qreal threeDHeight,
        qreal angle )
{
    QPolygonF poly( 4 );
    const QPointF center = rect.center();
    const QPointF circlePoint = pointOnEllipse( rect, angle );
    poly[0] = center;
    poly[1] = circlePoint;
    poly[2] = QPointF( circlePoint.x(), circlePoint.y() + threeDHeight );
    poly[3] = QPointF( center.x(), center.y() + threeDHeight );
    // TODO: add polygon to ReverseMapper
    painter->drawPolygon( poly );
}

void PieDiagram::draw3dOuterRim( QPainter* painter,
        const QRectF& rect,
        qreal threeDHeight,
        qreal startAngle,
        qreal endAngle )
{
    // Start with getting the points for the inner arc.
    if ( endAngle < startAngle ) {
        endAngle += 360;
    }
    startAngle = qMax( startAngle, qreal( 180.0 ) );
    endAngle = qMin( endAngle, qreal( 360.0 ) );

    int numHalfPoints = trunc( ( endAngle - startAngle ) / granularity() ) + 1;
    if ( numHalfPoints < 2 ) {
        return;
    }

    QPolygonF poly( numHalfPoints );

    qreal degree = endAngle;
    int iPoint = 0;
    bool perfectMatch = false;
    while ( degree >= startAngle ) {
        poly[ numHalfPoints - iPoint - 1 ] = pointOnEllipse( rect, degree );

        perfectMatch = (degree == startAngle);
        degree -= granularity();
        ++iPoint;
    }
    // if necessary add one more point to fill the last small gap
    if ( !perfectMatch ) {
        poly.prepend( pointOnEllipse( rect, startAngle ) );
        ++numHalfPoints;
    }

    poly.resize( numHalfPoints * 2 );

    // Now copy these arcs again into the final array, but in the
    // opposite direction and moved down by the 3D height.
    for ( int i = numHalfPoints - 1; i >= 0; --i ) {
        QPointF pointOnFirstArc( poly[ i ] );
        pointOnFirstArc.setY( pointOnFirstArc.y() + threeDHeight );
        poly[ numHalfPoints * 2 - i - 1 ] = pointOnFirstArc;
    }

    // TODO: Add polygon to ReverseMapper
    painter->drawPolygon( poly );
}

uint PieDiagram::findSliceAt( qreal angle, int colCount )
{
    for ( int i = 0; i < colCount; ++i ) {
        qreal endseg = d->startAngles[ i ] + d->angleLens[ i ];
        if ( d->startAngles[ i ] <= angle &&  endseg >= angle ) {
            return i;
        }
    }

    // If we have not found it, try wrap around
    // but only if the current searched angle is < 360 degree
    if ( angle < 360 )
        return findSliceAt( angle + 360, colCount );
    // otherwise - what ever went wrong - we return 0
    return 0;
}


uint PieDiagram::findLeftSlice( uint slice, int colCount )
{
    if ( slice == 0 ) {
        if ( colCount > 1 ) {
            return colCount - 1;
        } else {
            return 0;
        }
    } else {
        return slice - 1;
    }
}


uint PieDiagram::findRightSlice( uint slice, int colCount )
{
    int rightSlice = slice + 1;
    if ( rightSlice == colCount ) {
        rightSlice = 0;
    }
    return rightSlice;
}


QPointF PieDiagram::pointOnEllipse( const QRectF& boundingBox, qreal angle )
{
    qreal angleRad = DEGTORAD( angle );
    qreal cosAngle = cos( angleRad );
    qreal sinAngle = -sin( angleRad );
    qreal posX = cosAngle * boundingBox.width() / 2.0;
    qreal posY = sinAngle * boundingBox.height() / 2.0;
    return QPointF( posX + boundingBox.center().x(),
                    posY + boundingBox.center().y() );

}

/*virtual*/
qreal PieDiagram::valueTotals() const
{
    if ( !model() )
        return 0;
    const int colCount = columnCount();
    qreal total = 0.0;
    // non-empty models need a row with data
    Q_ASSERT( colCount == 0 || model()->rowCount() >= 1 );
    for ( int j = 0; j < colCount; ++j ) {
      total += qAbs(model()->data( model()->index( 0, j, rootIndex() ) ).toReal()); // checked
    }
    return total;
}

/*virtual*/
qreal PieDiagram::numberOfValuesPerDataset() const
{
    return model() ? model()->columnCount( rootIndex() ) : 0.0;
}

/*virtual*/
qreal PieDiagram::numberOfGridRings() const
{
    return 1;
}