Qt::QProxyStyle

QProxyStyle 修改控件默认系统样式，用于动态覆盖绘图或其他特定的样式行为。

实现自定义样式，需要自己定义一个类，从QProxyStyle派生，实现对应的虚函数即可。

#include <QProxyStyle>
#include <QPalette>

QT_BEGIN_NAMESPACE
class QPainterPath;
QT_END_NAMESPACE

class NorwegianWoodStyle : public QProxyStyle
{
    Q_OBJECT

public:
    NorwegianWoodStyle();

    QPalette standardPalette() const override;

    void polish(QWidget *widget) override;
    void unpolish(QWidget *widget) override;
    int pixelMetric(PixelMetric metric, const QStyleOption *option, const QWidget *widget) const override;
    int styleHint(StyleHint hint, const QStyleOption *option, const QWidget *widget, QStyleHintReturn *returnData) const override;
    void drawPrimitive(PrimitiveElement element, const QStyleOption *option, QPainter *painter, const QWidget *widget) const override;
    void drawControl(ControlElement control, const QStyleOption *option, QPainter *painter, const QWidget *widget) const override;

private:
    static void setTexture(QPalette &palette, QPalette::ColorRole role, const QImage &image);
    static QPainterPath roundRectPath(const QRect &rect);
    mutable QPalette m_standardPalette;
};

#include <QComboBox>
#include <QPainter>
#include <QPushButton>
#include <QStyleFactory>

NorwegianWoodStyle::NorwegianWoodStyle() :
    QProxyStyle(QStyleFactory::create("windows"))
{
    setObjectName("NorwegianWood");
}

QPalette NorwegianWoodStyle::standardPalette() const
{
    if (!m_standardPalette.isBrushSet(QPalette::Disabled, QPalette::Mid)) {
        QColor brown(212, 140, 95);
        QColor beige(236, 182, 120);
        QColor slightlyOpaqueBlack(0, 0, 0, 63);

        QImage backgroundImage(":/images/woodbackground.png");
        QImage buttonImage(":/images/woodbutton.png");
        QImage midImage = buttonImage.convertToFormat(QImage::Format_RGB32);

        QPainter painter;
        painter.begin(&midImage);
        painter.setPen(Qt::NoPen);
        painter.fillRect(midImage.rect(), slightlyOpaqueBlack);
        painter.end();
 
        QPalette palette(brown);

        palette.setBrush(QPalette::BrightText, Qt::white);
        palette.setBrush(QPalette::Base, beige);
        palette.setBrush(QPalette::Highlight, Qt::darkGreen);
        setTexture(palette, QPalette::Button, buttonImage);
        setTexture(palette, QPalette::Mid, midImage);
        setTexture(palette, QPalette::Window, backgroundImage);

        QBrush brush = palette.window();
        brush.setColor(brush.color().darker());

        palette.setBrush(QPalette::Disabled, QPalette::WindowText, brush);
        palette.setBrush(QPalette::Disabled, QPalette::Text, brush);
        palette.setBrush(QPalette::Disabled, QPalette::ButtonText, brush);
        palette.setBrush(QPalette::Disabled, QPalette::Base, brush);
        palette.setBrush(QPalette::Disabled, QPalette::Button, brush);
        palette.setBrush(QPalette::Disabled, QPalette::Mid, brush);

        m_standardPalette = palette;
    }

    return m_standardPalette;
}

void NorwegianWoodStyle::polish(QWidget *widget)

{
    if (qobject_cast<QPushButton *>(widget)
            || qobject_cast<QComboBox *>(widget))
        widget->setAttribute(Qt::WA_Hover, true);
}

void NorwegianWoodStyle::unpolish(QWidget *widget)
{
    if (qobject_cast<QPushButton *>(widget)
            || qobject_cast<QComboBox *>(widget))
        widget->setAttribute(Qt::WA_Hover, false);
}

int NorwegianWoodStyle::pixelMetric(PixelMetric metric,
                                    const QStyleOption *option,
                                    const QWidget *widget) const
{
    switch (metric) {
    case PM_ComboBoxFrameWidth:
        return 8;
    case PM_ScrollBarExtent:
        return QProxyStyle::pixelMetric(metric, option, widget) + 4;
    default:
        return QProxyStyle::pixelMetric(metric, option, widget);
    }
}

int NorwegianWoodStyle::styleHint(StyleHint hint, const QStyleOption *option,
                                  const QWidget *widget,
                                  QStyleHintReturn *returnData) const
{
    switch (hint) {
    case SH_DitherDisabledText:
        return int(false);
    case SH_EtchDisabledText:
        return int(true);
    default:
        return QProxyStyle::styleHint(hint, option, widget, returnData);
    }
}

void NorwegianWoodStyle::drawPrimitive(PrimitiveElement element,
                                           const QStyleOption *option,
                                           QPainter *painter,
                                           const QWidget *widget) const
{
    switch (element) 
    {
    case PE_PanelButtonCommand:
        {
            int delta = (option->state & State_MouseOver) ? 64 : 0;
            QColor slightlyOpaqueBlack(0, 0, 0, 63);
            QColor semiTransparentWhite(255, 255, 255, 127 + delta);
            QColor semiTransparentBlack(0, 0, 0, 127 - delta);

            int x, y, width, height;
            option->rect.getRect(&x, &y, &width, &height);
            
            QPainterPath roundRect = roundRectPath(option->rect);
            int radius = qMin(width, height) / 2;
            QBrush brush;
            bool darker;

            const QStyleOptionButton *buttonOption =
                    qstyleoption_cast<const QStyleOptionButton *>(option);
            if (buttonOption
                    && (buttonOption->features & QStyleOptionButton::Flat)) {
                brush = option->palette.window();
                darker = (option->state & (State_Sunken | State_On));
            } else {
                if (option->state & (State_Sunken | State_On)) {
                    brush = option->palette.mid();
                    darker = !(option->state & State_Sunken);
                } else {
                    brush = option->palette.button();
                    darker = false;
                }
            }

            painter->save();
            painter->setRenderHint(QPainter::Antialiasing, true);
            painter->fillPath(roundRect, brush);

            if (darker)
                painter->fillPath(roundRect, slightlyOpaqueBlack);

            int penWidth;

            if (radius < 10)
                penWidth = 3;
            else if (radius < 20)
                penWidth = 5;
            else
                penWidth = 7;

            QPen topPen(semiTransparentWhite, penWidth);
            QPen bottomPen(semiTransparentBlack, penWidth);

            if (option->state & (State_Sunken | State_On))
                qSwap(topPen, bottomPen);

            int x1 = x;
            int x2 = x + radius;
            int x3 = x + width - radius;
            int x4 = x + width;

            if (option->direction == Qt::RightToLeft) {
                qSwap(x1, x4);
                qSwap(x2, x3);
            }

            QPolygon topHalf;
            topHalf << QPoint(x1, y)
                    << QPoint(x4, y)
                    << QPoint(x3, y + radius)
                    << QPoint(x2, y + height - radius)
                    << QPoint(x1, y + height);

            painter->setClipPath(roundRect);
            painter->setClipRegion(topHalf, Qt::IntersectClip);
            painter->setPen(topPen);
            painter->drawPath(roundRect);

            QPolygon bottomHalf = topHalf;
            bottomHalf[0] = QPoint(x4, y + height);

            painter->setClipPath(roundRect);
            painter->setClipRegion(bottomHalf, Qt::IntersectClip);
            painter->setPen(bottomPen);
            painter->drawPath(roundRect);

            painter->setPen(option->palette.windowText().color());
            painter->setClipping(false);
            painter->drawPath(roundRect);

            painter->restore();
        }
        break;
    default:
        QProxyStyle::drawPrimitive(element, option, painter, widget);
    }
}

void NorwegianWoodStyle::drawControl(ControlElement element,
    const QStyleOption *option,
    QPainter *painter,
    const QWidget *widget) const
{
    switch (element) {
    case CE_PushButtonLabel:
        {
            QStyleOptionButton myButtonOption;
            const QStyleOptionButton *buttonOption =
                    qstyleoption_cast<const QStyleOptionButton *>(option);
            if (buttonOption) {
                myButtonOption = *buttonOption;
                if (myButtonOption.palette.currentColorGroup()
                        != QPalette::Disabled) {
                    if (myButtonOption.state & (State_Sunken | State_On)) {
                        myButtonOption.palette.setBrush(QPalette::ButtonText,
                                myButtonOption.palette.brightText());
                    }
                }
            }
            QProxyStyle::drawControl(element, &myButtonOption, painter, widget);
        }
        break;
    default:
        QProxyStyle::drawControl(element, option, painter, widget);
    }
}

void NorwegianWoodStyle::setTexture(QPalette &palette, QPalette::ColorRole role, const QImage &image)
{
    for (int i = 0; i < QPalette::NColorGroups; ++i) {
        QBrush brush(image);
        brush.setColor(palette.brush(QPalette::ColorGroup(i), role).color());
        palette.setBrush(QPalette::ColorGroup(i), role, brush);
    }
}

QPainterPath NorwegianWoodStyle::roundRectPath(const QRect &rect)
{
    int radius = qMin(rect.width(), rect.height()) / 2;
    int diam = 2 * radius;

    int x1, y1, x2, y2;
    rect.getCoords(&x1, &y1, &x2, &y2);

    QPainterPath path;
    path.moveTo(x2, y1 + radius);
    path.arcTo(QRect(x2 - diam, y1, diam, diam), 0.0, +90.0);
    path.lineTo(x1 + radius, y1);
    path.arcTo(QRect(x1, y1, diam, diam), 90.0, +90.0);
    path.lineTo(x1, y2 - radius);
    path.arcTo(QRect(x1, y2 - diam, diam, diam), 180.0, +90.0);
    path.lineTo(x1 + radius, y2);
    path.arcTo(QRect(x2 - diam, y2 - diam, diam, diam), 270.0, +90.0);
    path.closeSubpath();
    return path;
}

void changeStyle(const QString &styleName)
{
    if (styleName == "NorwegianWood")
        QApplication::setStyle(new NorwegianWoodStyle);
    else
        QApplication::setStyle(QStyleFactory::create(styleName));
}