C++ QBezier类代码示例

qreal QBezier::tAtLength(qreal l) const
{
    qreal len = length();
    qreal t   = qreal(1.0);
    const qreal error = qreal(0.01);
    if (l > len || qFuzzyCompare(l, len))
        return t;

    t *= qreal(0.5);
    //int iters = 0;
    //qDebug()<<"LEN is "<<l<<len;
    qreal lastBigger = qreal(1.0);
    while (1) {
        //qDebug()<<"\tt is "<<t;
        QBezier right = *this;
        QBezier left;
        right.parameterSplitLeft(t, &left);
        qreal lLen = left.length();
        if (qAbs(lLen - l) < error)
            break;

        if (lLen < l) {
            t += (lastBigger - t) * qreal(0.5);
        } else {
            lastBigger = t;
            t -= t * qreal(0.5);
        }
        //++iters;
    }
    //qDebug()<<"number of iters is "<<iters;
    return t;
}

void QBezier::addToPolygon(QPolygonF *polygon, qreal bezier_flattening_threshold) const
{
    QBezier beziers[32];
    beziers[0] = *this;
    QBezier *b = beziers;

    while (b >= beziers) {
        // check if we can pop the top bezier curve from the stack
        qreal y4y1 = b->y4 - b->y1;
        qreal x4x1 = b->x4 - b->x1;
        qreal l = qAbs(x4x1) + qAbs(y4y1);
        qreal d;
        if (l > 1.) {
            d = qAbs( (x4x1)*(b->y1 - b->y2) - (y4y1)*(b->x1 - b->x2) )
                + qAbs( (x4x1)*(b->y1 - b->y3) - (y4y1)*(b->x1 - b->x3) );
        } else {
            d = qAbs(b->x1 - b->x2) + qAbs(b->y1 - b->y2) +
                qAbs(b->x1 - b->x3) + qAbs(b->y1 - b->y3);
            l = 1.;
        }
        if (d < bezier_flattening_threshold*l || b == beziers + 31) {
            // good enough, we pop it off and add the endpoint
            polygon->append(QPointF(b->x4, b->y4));
            --b;
        } else {
            // split, second half of the polygon goes lower into the stack
            b->split(b+1, b);
            ++b;
        }
    }
}

int QBezier::shifted(QBezier *curveSegments, int maxSegments, qreal offset, float threshold) const
{
    Q_ASSERT(curveSegments);
    Q_ASSERT(maxSegments > 0);

    if (x1 == x2 && x1 == x3 && x1 == x4 &&
        y1 == y2 && y1 == y3 && y1 == y4)
        return 0;

    --maxSegments;
    QBezier beziers[10];
redo:
    beziers[0] = *this;
    QBezier *b = beziers;
    QBezier *o = curveSegments;

    while (b >= beziers) {
        int stack_segments = b - beziers + 1;
        if ((stack_segments == 10) || (o - curveSegments == maxSegments - stack_segments)) {
            threshold *= qreal(1.5);
            if (threshold > qreal(2.0))
                goto give_up;
            goto redo;
        }
        ShiftResult res = shift(b, o, offset, threshold);
        if (res == Discard) {
            --b;
        } else if (res == Ok) {
            ++o;
            --b;
            continue;
        } else if (res == Circle && maxSegments - (o - curveSegments) >= 2) {
            // add semi circle
            if (addCircle(b, offset, o))
                o += 2;
            --b;
        } else {
            b->split(b+1, b);
            ++b;
        }
    }

give_up:
    while (b >= beziers) {
        ShiftResult res = shift(b, o, offset, threshold);

        // if res isn't Ok or Split then *o is undefined
        if (res == Ok || res == Split)
            ++o;

        --b;
    }

    Q_ASSERT(o - curveSegments <= maxSegments);
    return o - curveSegments;
}

void QOutlineMapper::curveTo(const QPointF &cp1, const QPointF &cp2, const QPointF &ep) {
#ifdef QT_DEBUG_CONVERT
    printf("QOutlineMapper::curveTo() (%f, %f)\n", ep.x(), ep.y());
#endif

    QBezier bezier = QBezier::fromPoints(m_elements.last(), cp1, cp2, ep);
    bezier.addToPolygon(m_elements, m_curve_threshold);
    m_element_types.reserve(m_elements.size());
    for (int i = m_elements.size() - m_element_types.size(); i; --i)
        m_element_types << QPainterPath::LineToElement;
    Q_ASSERT(m_elements.size() == m_element_types.size());
}

QBezier QBezier::bezierOnInterval(qreal t0, qreal t1) const
{
    if (t0 == 0 && t1 == 1)
        return *this;

    QBezier bezier = *this;

    QBezier result;
    bezier.parameterSplitLeft(t0, &result);
    qreal trueT = (t1-t0)/(1-t0);
    bezier.parameterSplitLeft(trueT, &result);

    return result;
}

QBezier QBezier::getSubRange(qreal t0, qreal t1) const
{
    QBezier result;
    QBezier temp;

    // cut at t1
    if (qFuzzyIsNull(t1 - qreal(1.))) {
        result = *this;
    } else {
        temp = *this;
        temp.parameterSplitLeft(t1, &result);
    }

    // cut at t0
    if (!qFuzzyIsNull(t0))
        result.parameterSplitLeft(t0 / t1, &temp);

    return result;
}

void QBezier::addToPolygon(QDataBuffer<QPointF> &polygon, qreal bezier_flattening_threshold) const
{
    QBezier beziers[10];
    int levels[10];
    beziers[0] = *this;
    levels[0] = 9;
    QBezier *b = beziers;
    int *lvl = levels;

    while (b >= beziers) {
        // check if we can pop the top bezier curve from the stack
        qreal y4y1 = b->y4 - b->y1;
        qreal x4x1 = b->x4 - b->x1;
        qreal l = qAbs(x4x1) + qAbs(y4y1);
        qreal d;
        if (l > 1.) {
            d = qAbs( (x4x1)*(b->y1 - b->y2) - (y4y1)*(b->x1 - b->x2) )
                + qAbs( (x4x1)*(b->y1 - b->y3) - (y4y1)*(b->x1 - b->x3) );
        } else {
            d = qAbs(b->x1 - b->x2) + qAbs(b->y1 - b->y2) +
                qAbs(b->x1 - b->x3) + qAbs(b->y1 - b->y3);
            l = 1.;
        }
        if (d < bezier_flattening_threshold*l || *lvl == 0) {
            // good enough, we pop it off and add the endpoint
            polygon.add(QPointF(b->x4, b->y4));
            --b;
            --lvl;
        } else {
            // split, second half of the polygon goes lower into the stack
            b->split(b+1, b);
            lvl[1] = --lvl[0];
            ++b;
            ++lvl;
        }
    }
}

void QGL2PEXVertexArray::addPath(const QVectorPath &path, GLfloat curveInverseScale, bool outline)
{
    const QPointF* const points = reinterpret_cast<const QPointF*>(path.points());
    const QPainterPath::ElementType* const elements = path.elements();

    if (boundingRectDirty) {
        minX = maxX = points[0].x();
        minY = maxY = points[0].y();
        boundingRectDirty = false;
    }

    if (!outline && !path.isConvex())
        addCentroid(path, 0);

    int lastMoveTo = vertexArray.size();
    vertexArray.add(points[0]); // The first element is always a moveTo

    do {
        if (!elements) {
//             qDebug("QVectorPath has no elements");
            // If the path has a null elements pointer, the elements implicitly
            // start with a moveTo (already added) and continue with lineTos:
            for (int i=1; i<path.elementCount(); ++i)
                lineToArray(points[i].x(), points[i].y());

            break;
        }
//         qDebug("QVectorPath has element types");

        for (int i=1; i<path.elementCount(); ++i) {
            switch (elements[i]) {
            case QPainterPath::MoveToElement:
                if (!outline)
                    addClosingLine(lastMoveTo);
//                qDebug("element[%d] is a MoveToElement", i);
                vertexArrayStops.add(vertexArray.size());
                if (!outline) {
                    if (!path.isConvex()) addCentroid(path, i);
                    lastMoveTo = vertexArray.size();
                }
                lineToArray(points[i].x(), points[i].y()); // Add the moveTo as a new vertex
                break;
            case QPainterPath::LineToElement:
//                qDebug("element[%d] is a LineToElement", i);
                lineToArray(points[i].x(), points[i].y());
                break;
            case QPainterPath::CurveToElement: {
                QBezier b = QBezier::fromPoints(*(((const QPointF *) points) + i - 1),
                                                points[i],
                                                points[i+1],
                                                points[i+2]);
                QRectF bounds = b.bounds();
                // threshold based on same algorithm as in qtriangulatingstroker.cpp
                int threshold = qMin<float>(64, qMax(bounds.width(), bounds.height()) * 3.14f / (curveInverseScale * 6));
                if (threshold < 3) threshold = 3;
                qreal one_over_threshold_minus_1 = qreal(1) / (threshold - 1);
                for (int t=0; t<threshold; ++t) {
                    QPointF pt = b.pointAt(t * one_over_threshold_minus_1);
                    lineToArray(pt.x(), pt.y());
                }
                i += 2;
                break; }
            default:
                break;
            }
        }
    } while (0);

    if (!outline)
        addClosingLine(lastMoveTo);
    vertexArrayStops.add(vertexArray.size());
}

void QDashedStrokeProcessor::process(const QVectorPath &path, const QPen &pen)
{

    const qreal *pts = path.points();
    const QPainterPath::ElementType *types = path.elements();
    int count = path.elementCount();

    m_points.reset();
    m_types.reset();

    qreal width = qpen_widthf(pen);
    if (width == 0)
        width = 1;

    m_dash_stroker.setDashPattern(pen.dashPattern());
    m_dash_stroker.setStrokeWidth(pen.isCosmetic() ? width * m_inv_scale : width);
    m_dash_stroker.setMiterLimit(pen.miterLimit());
    qreal curvyness = sqrt(width) * m_inv_scale / 8;

    if (count < 2)
        return;

    const qreal *endPts = pts + (count<<1);

    m_dash_stroker.begin(this);

    if (!types) {
        m_dash_stroker.moveTo(pts[0], pts[1]);
        pts += 2;
        while (pts < endPts) {
            m_dash_stroker.lineTo(pts[0], pts[1]);
            pts += 2;
        }
    } else {
        while (pts < endPts) {
            switch (*types) {
            case QPainterPath::MoveToElement:
                m_dash_stroker.moveTo(pts[0], pts[1]);
                pts += 2;
                ++types;
                break;
            case QPainterPath::LineToElement:
                m_dash_stroker.lineTo(pts[0], pts[1]);
                pts += 2;
                ++types;
                break;
            case QPainterPath::CurveToElement: {
                QBezier b = QBezier::fromPoints(*(((const QPointF *) pts) - 1),
                                                *(((const QPointF *) pts)),
                                                *(((const QPointF *) pts) + 1),
                                                *(((const QPointF *) pts) + 2));
                QRectF bounds = b.bounds();
                int threshold = qMin<float>(64, qMax(bounds.width(), bounds.height()) * curvyness);
                if (threshold < 4)
                    threshold = 4;
                qreal threshold_minus_1 = threshold - 1;
                for (int i=0; i<threshold; ++i) {
                    QPointF pt = b.pointAt(i / threshold_minus_1);
                    m_dash_stroker.lineTo(pt.x(), pt.y());
                }
                pts += 6;
                types += 3;
                break; }
            default: break;
            }
        }
    }

    m_dash_stroker.end();
}