效果图：

目录结构：

头文件：

#ifndef MYWIDGET_H
#define MYWIDGET_H

#include <QMainWindow>

namespace Ui {
class MyWidget;
}

class MyWidget : public QMainWindow
{
    Q_OBJECT

public:
    explicit MyWidget(QWidget *parent = 0);
    ~MyWidget();
     void paintEvent(QPaintEvent *event);


private:
    Ui::MyWidget *ui;
   int crossCenterX;
   int crossCenterY;
   QTimer *timer;
   int step;
   bool isReverse;
};

#endif // MYWIDGET_H

源文件：

#include "mywidget.h"
#include "ui_mywidget.h"
#include <QPainter>
#include <QTimer>
MyWidget::MyWidget(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MyWidget)
{
    ui->setupUi(this);
    //设置窗体的大小
    this->resize(512,512);
    //设置中心点的坐标，保存为变量
    crossCenterX=this->width()/2;
    crossCenterY=this->height()/2;
    //设置定时器，时间间隔围为80ms
    timer=new QTimer(this);
    step=-100;
    isReverse=false;
    //设置定时触发信号，在定时信号处理的槽函数中，判断当前的偏移量是否够在±100范围内
    //当超出边界范围时，改变方向标记h
    connect(timer,&QTimer::timeout,[=](){
        if(step>100){
            isReverse=true;
        }else if(step<-100) {
            isReverse=false;
        }
        update();
    });
    timer->setInterval(80);
    timer->start();

}

MyWidget::~MyWidget()
{
    delete ui;
}
void MyWidget::paintEvent(QPaintEvent *event){
    QPainter painter(this);
    painter.setBrush(Qt::black);
    painter.drawRect(rect());
    painter.setPen(Qt::white);
    //绘制文字
    QFont font;
    font.setPointSize(20);
    painter.setFont(font);
    painter.drawText(20,40,"TV");
    //绘制右下角图片
    painter.drawPixmap(this->width()-128,this->height()-128,128,128,QPixmap(":/Images/test.png"));
    //水平线
    painter.drawLine(QPoint(crossCenterX-256/2+step,crossCenterY),QPoint(crossCenterX+256/2+step,crossCenterY));
    painter.drawLine(QPoint(crossCenterX+step,crossCenterY-256/2),QPoint(crossCenterX+step,crossCenterY+256/2));
    if(!isReverse) {
        step+=3;//向正方向运行
    }else{
        step-=3;//向反方向运行
    }


}

搜素：TestWidget.zip可以找到资源