Qt编写自定义控件：文字聚光灯效果之一

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>
#include <QTimer>

class Widget : public QWidget
{
    Q_OBJECT

public:
    Widget(QWidget *parent = nullptr);
    ~Widget();

protected:
    void paintEvent(QPaintEvent *event)override;

private:
    void onTimer();
    QString text;
    QTimer timer;
    QRect textRect;
    int changeValue{0};
    bool runDirectionIsRight{true};
};
#endif // WIDGET_H

#include "widget.h"
#include <QPainter>
#include <QPaintEvent>
#include <QPainterPath>

Widget::Widget(QWidget *parent)
    : QWidget(parent)
{
    text = "黄河之水天上来，奔流到海不复回";
    auto font = this->font();
    font.setPixelSize(40);
    font.setBold(true);
    setFont(font);

    connect(&timer,&QTimer::timeout,this,&Widget::onTimer);
    timer.start(40);
}

Widget::~Widget()
{
}

void Widget::paintEvent(QPaintEvent *event)
{
    QPainter painter(this);
    painter.setRenderHint(QPainter::Antialiasing,true);
    painter.setFont(this->font());
    auto rect = event->rect();

    painter.save();
    painter.setPen(QColor("#574E54"));
    painter.drawText(rect, Qt::AlignCenter | Qt::TextWordWrap, text);
    painter.restore();
    textRect = painter.boundingRect(rect,Qt::AlignCenter | Qt::TextWordWrap,text);

    auto pos = textRect.topLeft() + QPoint(changeValue,0);
    QPolygon polygon;
    polygon << pos << pos + QPoint(50,0);
    pos = textRect.bottomLeft() + QPoint(changeValue,0);
    polygon << pos + QPoint(25,0) << pos - QPoint(25,0);;

    QPainterPath path;
    path.addPolygon(polygon);
    painter.setClipPath(path);

    auto tempRect = polygon.boundingRect();
    QLinearGradient linearGradient(tempRect.topRight(),tempRect.bottomLeft());
    linearGradient.setColorAt(0.0,Qt::magenta);
    linearGradient.setColorAt(0.2,Qt::darkYellow);
    linearGradient.setColorAt(0.4,Qt::green);
    linearGradient.setColorAt(0.6,Qt::red);
    linearGradient.setColorAt(0.8,Qt::darkRed);
    linearGradient.setColorAt(1.0,Qt::blue);
    painter.setBrush(Qt::transparent);
    painter.setPen(QPen(QBrush(linearGradient),3));

    painter.drawText(rect, Qt::AlignCenter | Qt::TextWordWrap, text);
}

void Widget::onTimer()
{
    if(runDirectionIsRight)
    {
        changeValue += 15;
        if(changeValue >= textRect.width())
        {
            runDirectionIsRight = false;
        }
    }
    else
    {
        changeValue -= 15;
        if(changeValue <= 0)
        {
            runDirectionIsRight = true;
        }
    }
    update();
}