QFD2/QFD/qcustomplot/SmoothCurveGraph.cpp

#include "SmoothCurveGraph.h"

#include <QPointF>
#include <QVector>

class SmoothCurveGenerator
{
protected:
    static QPainterPath generateSmoothCurveImp(const QVector<QPointF> &points)
    {
        QPainterPath path;
        int len = points.size();

        if (len < 2) {
            return path;
        }

        QVector<QPointF> firstControlPoints;
        QVector<QPointF> secondControlPoints;
        calculateControlPoints(points, &firstControlPoints, &secondControlPoints);

        path.moveTo(points[0].x(), points[0].y());

        // Using bezier curve to generate a smooth curve.
        for (int i = 0; i < len - 1; ++i) {
            path.cubicTo(firstControlPoints[i], secondControlPoints[i], points[i + 1]);
        }

        return path;
    }

public:
    static QPainterPath generateSmoothCurve(const QVector<QPointF> &points)
    {
        QPainterPath result;

        int segmentStart = 0;
        int i            = 0;
        int pointSize    = points.size();
        while (i < pointSize) {
            if (qIsNaN(points.at(i).y()) || qIsNaN(points.at(i).x()) || qIsInf(points.at(i).y())) {
                QVector<QPointF> lineData;  // QVector<QPointF>(points.constBegin() + segmentStart, points.constBegin()
                                            // + i - segmentStart);
                for (int s = segmentStart; s < i - segmentStart; ++s) {
                    lineData << points.at(s);
                }

                result.addPath(generateSmoothCurveImp(lineData));
                segmentStart = i + 1;
            }
            ++i;
        }
        QVector<QPointF> lineData;  //(QVector<QPointF>(points.constBegin() + segmentStart, points.constEnd()));
        for (int s = segmentStart; s < points.size(); ++s) {
            lineData << points.at(s);
        }
        result.addPath(generateSmoothCurveImp(lineData));
        return result;
    }

    static QPainterPath generateSmoothCurve(const QPainterPath &basePath, const QVector<QPointF> &points)
    {
        if (points.isEmpty())
            return basePath;

        QPainterPath path = basePath;
        int len           = points.size();
        if (len == 1) {
            path.lineTo(points.at(0));
            return path;
        }

        QVector<QPointF> firstControlPoints;
        QVector<QPointF> secondControlPoints;
        calculateControlPoints(points, &firstControlPoints, &secondControlPoints);

        path.lineTo(points.at(0));
        for (int i = 0; i < len - 1; ++i)
            path.cubicTo(firstControlPoints[i], secondControlPoints[i], points[i + 1]);

        return path;
    }

    static void calculateFirstControlPoints(double *&result, const double *rhs, int n)
    {
        result      = new double[n];
        double *tmp = new double[n];
        double b    = 2.0;
        result[0]   = rhs[0] / b;

        // Decomposition and forward substitution.
        for (int i = 1; i < n; i++) {
            tmp[i]    = 1 / b;
            b         = (i < n - 1 ? 4.0 : 3.5) - tmp[i];
            result[i] = (rhs[i] - result[i - 1]) / b;
        }

        for (int i = 1; i < n; i++) {
            result[n - i - 1] -= tmp[n - i] * result[n - i];  // Backsubstitution.
        }

        delete[] tmp;
    }

    static void calculateControlPoints(const QVector<QPointF> &knots, QVector<QPointF> *firstControlPoints,
                                       QVector<QPointF> *secondControlPoints)
    {
        int n = knots.size() - 1;

        firstControlPoints->reserve(n);
        secondControlPoints->reserve(n);

        for (int i = 0; i < n; ++i) {
            firstControlPoints->append(QPointF());
            secondControlPoints->append(QPointF());
        }

        if (n == 1) {
            // Special case: Bezier curve should be a straight line.
            // P1 = (2P0 + P3) / 3
            (*firstControlPoints)[0].rx() = (2 * knots[0].x() + knots[1].x()) / 3;
            (*firstControlPoints)[0].ry() = (2 * knots[0].y() + knots[1].y()) / 3;

            // P2 = 2P1 – P0
            (*secondControlPoints)[0].rx() = 2 * (*firstControlPoints)[0].x() - knots[0].x();
            (*secondControlPoints)[0].ry() = 2 * (*firstControlPoints)[0].y() - knots[0].y();

            return;
        }

        // Calculate first Bezier control points
        double *xs   = nullptr;
        double *ys   = nullptr;
        double *rhsx = new double[n];  // Right hand side vector
        double *rhsy = new double[n];  // Right hand side vector

        // Set right hand side values
        for (int i = 1; i < n - 1; ++i) {
            rhsx[i] = 4 * knots[i].x() + 2 * knots[i + 1].x();
            rhsy[i] = 4 * knots[i].y() + 2 * knots[i + 1].y();
        }
        rhsx[0]     = knots[0].x() + 2 * knots[1].x();
        rhsx[n - 1] = (8 * knots[n - 1].x() + knots[n].x()) / 2.0;
        rhsy[0]     = knots[0].y() + 2 * knots[1].y();
        rhsy[n - 1] = (8 * knots[n - 1].y() + knots[n].y()) / 2.0;

        // Calculate first control points coordinates
        calculateFirstControlPoints(xs, rhsx, n);
        calculateFirstControlPoints(ys, rhsy, n);

        // Fill output control points.
        for (int i = 0; i < n; ++i) {
            (*firstControlPoints)[i].rx() = xs[i];
            (*firstControlPoints)[i].ry() = ys[i];

            if (i < n - 1) {
                (*secondControlPoints)[i].rx() = 2 * knots[i + 1].x() - xs[i + 1];
                (*secondControlPoints)[i].ry() = 2 * knots[i + 1].y() - ys[i + 1];
            } else {
                (*secondControlPoints)[i].rx() = (knots[n].x() + xs[n - 1]) / 2;
                (*secondControlPoints)[i].ry() = (knots[n].y() + ys[n - 1]) / 2;
            }
        }

        delete xs;
        delete ys;
        delete[] rhsx;
        delete[] rhsy;
    }
};

SmoothCurveGraph::SmoothCurveGraph(QCPAxis *keyAxis, QCPAxis *valueAxis) : QCPGraph(keyAxis, valueAxis), m_smooth(true)
{
}

void SmoothCurveGraph::setSmooth(bool smooth)
{
    m_smooth = smooth;
}

void SmoothCurveGraph::drawLinePlot(QCPPainter *painter, const QVector<QPointF> &lines) const
{
    if (painter->pen().style() != Qt::NoPen && painter->pen().color().alpha() != 0) {
        applyDefaultAntialiasingHint(painter);
        if (m_smooth && mLineStyle == lsLine)
            painter->drawPath(SmoothCurveGenerator::generateSmoothCurve(lines));
        else
            drawPolyline(painter, lines);
    }
}