qt-everywhere-src-5.15.1/qtlottie/src/bodymovin/beziereasing.cpp

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#include <beziereasing_p.h>

QT_BEGIN_NAMESPACE

void BezierEasing::addCubicBezierSegment(const QPointF &c1, const QPointF &c2, const QPointF &endPoint)
{
    mBezier = QBezier::fromPoints(QPointF(0.0, 0.0), c1, c2, endPoint);
}

qreal BezierEasing::valueForProgress(qreal progress) const
{
    qreal res = mBezier.pointAt(tForX(progress)).y();
    return qBound(qreal(0.0), res, qreal(1.0));
}

qreal BezierEasing::tForX(qreal x) const
{
    if (x <= 0.0)
        return 0.0;
    else if (x >= 1.0)
        return 1.0;

    qreal t0 = 0.0;
    qreal t1 = 1.0;

    for (int i = 0; i < 10; i++) {  // 10 iterations gives error smaller than 0.001
        qreal t = qreal(0.5) * (t0 + t1);
        qreal a, b, c, d;
        QBezier::coefficients(t, a, b, c, d);
        qreal xt = a * mBezier.x1 + b * mBezier.x2 + c * mBezier.x3 + d * mBezier.x4;
        if (xt < x)
            t0 = t;
        else
            t1 = t;
    }

    return t0;
}

QT_END_NAMESPACE