qt-everywhere-src-5.14.1/qtquickcontrols2/src/imports/controls/fusion/qquickfusionknob.cpp

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#include "qquickfusionknob_p.h"

#include <QtCore/qmath.h>
#include <QtGui/qpainter.h>

QT_BEGIN_NAMESPACE

QQuickFusionKnob::QQuickFusionKnob(QQuickItem *parent)
    : QQuickPaintedItem(parent)
{
}

QPalette QQuickFusionKnob::palette() const
{
    return m_palette;
}

void QQuickFusionKnob::setPalette(const QPalette &palette)
{
    if (palette == m_palette)
        return;

    m_palette = palette;
    update();
}

// extracted from QStyleHelper::drawDial()
void QQuickFusionKnob::paint(QPainter *painter)
{
    const qreal w = width();
    const qreal h = height();
    if (w <= 0 || h <= 0)
        return;

    QColor color = m_palette.color(QPalette::Button);
    color.setHsv(color.hue(),
                 qMin(140, color .saturation()),
                 qMax(180, color.value()));
    color = color.lighter(104);
    color.setAlphaF(qreal(0.8));

    const qreal sz = qMin(w, h);
    QRectF rect(0, 0, sz, sz);
    rect.moveCenter(QPointF(w / 2.0, h / 2.0));
    const QPointF center = rect.center();

    QRadialGradient gradient(center.x() + rect.width() / 2,
                             center.y() + rect.width(),
                             rect.width() * 2,
                             center.x(), center.y());
    gradient.setColorAt(1, color.darker(140));
    gradient.setColorAt(qreal(0.4), color.darker(120));
    gradient.setColorAt(0, color.darker(110));

    painter->setRenderHint(QPainter::Antialiasing);
    painter->setBrush(gradient);
    painter->setPen(QColor(255, 255, 255, 150));
    painter->drawEllipse(rect);
    painter->setPen(QColor(0, 0, 0, 80));
    painter->drawEllipse(rect.adjusted(1, 1, -1, -1));
}

QT_END_NAMESPACE