使用QT设计一个简单的时钟

先上效果图：

预备知识：
一.钟表实现原理
设置定时器timer，每隔1000毫秒（即1s）发送timeout()信号到槽函数update（），重绘事件函数paintEvent(QPaintEventevent)
二.钟表的绘制方法
拆分钟表：表盘 数字 刻度线 指针
paintEvent(QPaintEventevent)
1.设置定时器，时间间隔为1000毫秒，并且将定时器时间与update函数关联为信号和槽，定时器每隔1秒发送一个信号
2.绘制时针分针秒针的形状。

  // 时针、分针、秒针 - 多边形
    static const QPoint hourHand[3] = {
        QPoint(3, 8),
        QPoint(-3, 8),
        QPoint(0, -40)
    };


    static const QPoint minuteHand[3] = {
        QPoint(3, 8),
        QPoint(-3, 8),
        QPoint(0, -65)
    };


    static const QPoint secondHand[3] = {
        QPoint(3, 8),
        QPoint(-3, 8),
        QPoint(0, -80)
    };

3.绘制时针和时刻度线

     // 绘制时针
        painter.setPen(Qt::NoPen);
        painter.setBrush(hourColor);
        painter.save();
        painter.rotate(30.0 * ((time.hour() + time.minute() / 60.0)));
        painter.drawConvexPolygon(hourHand, 3);
        painter.restore();
        painter.setPen(hourColor);
            // 绘制时刻度线
        for (int i = 0; i < 12; ++i)
        {
            painter.drawLine(88, 0, 96, 0);
            painter.rotate(30.0);
        }
        QFont font = painter.font();
        font.setBold(true);
        painter.setFont(font);

下面是一些基础的绘图函数：
drawPoint() 绘制点
drawLine() 绘制线
drawRect() 绘制矩形
drawEllipse() 绘制椭圆（绘制圆也是此函数）
drawConvexPolygon() 绘制凸多边形
drawText（） 编制文本

特别的，我们还会经常用到
QPen：绘制几何图形的边缘，可绘制颜色，宽度，线的风格等
QBrush：用于几何图形的调色板与填充
则可借用setPen（）来当做画笔来使用。
setBrush（）来当做填充器使用来填充颜色。
setPen(color)；
然后我们的绘制将会用此颜色的画笔来绘制图形边缘。
setBrush(color)；

主要代码展示：

void Widget::drawhourhand(QPainter*painter)
{
    QTime time=QTime::currentTime();
    painter->setBrush(Qt::blue);//画刷，填充
    painter->setPen(Qt::Dense7Pattern);//画笔，制作廓线
    painter->save();
    painter->rotate(30.0*(time.hour()+time.minute()/60));//使得指针旋转到当前时间位置
    painter->drawConvexPolygon(hourhand,4);;//绘制时针（凸多边形）
    painter->restore();//与save连着用 绘制图形后复位坐标系
}
void Widget::drawminutehand(QPainter*painter)
{
    QTime time=QTime::currentTime();
    painter->setBrush(Qt::white);
    painter->setPen(Qt::Dense5Pattern);
    painter->save();
    painter->rotate(6.0*(time.minute()+time.second()/60.0));
    painter->drawConvexPolygon(minutehand,4);
    painter->restore();
}
void Widget::drawsecondhand(QPainter*painter)
{
    QTime time=QTime::currentTime();
    painter->setBrush(Qt::red);
    painter->setPen(Qt::Dense5Pattern);
    painter->save();
    painter->rotate(6*time.second());
    painter->drawPolygon(minutehand,4);
    painter->restore();
}
``


```cpp
#include "widget.h"
#include "ui_widget.h"


Widget::Widget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Widget)
{
    ui->setupUi(this);
    font.setPixelSize(10);
    setFont(font);
    setWindowTitle("THE CLOCK");
    resize(1200,820);
}


Widget::~Widget()
{
    delete ui;
}
const QPoint Widget::hourhand[4]={
     QPoint(5,5),QPoint(0,13),QPoint(-5,5),QPoint(0,-40)
};
const QPoint Widget::minutehand[4]={
     QPoint(3,5),QPoint(0,16),QPoint(-3,5),QPoint(0,-70)
};
const QPoint Widget::secondhand[4]={
     QPoint(0,0),QPoint(0,0),QPoint(0,0),QPoint(0,0)
};
void Widget::drawhourhand(QPainter*painter)
{
    QTime time=QTime::currentTime();
    painter->setBrush(Qt::blue);//画刷，填充
    painter->setPen(Qt::Dense7Pattern);//画笔，制作廓线
    painter->save();
    painter->rotate(30.0*(time.hour()+time.minute()/60));//使得指针旋转到当前时间位置
    painter->drawConvexPolygon(hourhand,4);;//绘制时针（凸多边形）
    painter->restore();//与save连着用 绘制图形后复位坐标系
}
void Widget::drawminutehand(QPainter*painter)
{
    QTime time=QTime::currentTime();
    painter->setBrush(Qt::white);
    painter->setPen(Qt::Dense5Pattern);
    painter->save();
    painter->rotate(6.0*(time.minute()+time.second()/60.0));
    painter->drawConvexPolygon(minutehand,4);
    painter->restore();
}
void Widget::drawsecondhand(QPainter*painter)
{
    QTime time=QTime::currentTime();
    painter->setBrush(Qt::red);
    painter->setPen(Qt::Dense5Pattern);
    painter->save();
    painter->rotate(6.0*time.second());
    painter->drawPolygon(minutehand,4);
    painter->restore();
}
void Widget::paintEvent(QPaintEvent*event)
{
    QPainter painter(this);
    QTimer*timer=new QTimer(this);
    timer->start(1000);
    connect(timer,SIGNAL(timeout()),this,SLOT(update()));
    QPixmap map(":/new/prefix1/timg (1).jfif");
    QRect q(0,0,1200,800);//截取这么大的面积
    QRect q2(0,0,width(),height());//放到指定大小的框中
    painter.drawPixmap(q2,map,q);
    painter.setRenderHint(QPainter::Antialiasing,true);//反走样
    int side=qMin(width(),height());
    painter.setWindow(0,0,230,230);//原本截取放大的面积区域多大
    painter.setViewport(96,0,side,side);//映射到新的区域面积多大
    painter.translate(100,100);//重新设定坐标原点
    drawhourhand(&painter);
    drawminutehand(&painter);
    drawsecondhand(&painter);
    drawclockdial(&painter);
    QString timeStr= QTime::currentTime().toString();     //绘制当前的电子时间
    painter.setPen(Qt::white);
    painter.drawText(-20,30,80,30,0,timeStr);
    painter.setBrush(Qt::black);
    painter.drawEllipse(QPoint(0,0),3,3);//中间画个小圆点
   // QTransform Transform;
   // Transform.rotate(90);
   // painter.setTransform(Transform);
    painter.drawText(-53,-30,QStringLiteral("老子利指导，杀人先看表"));
}
void Widget::drawclockdial(QPainter*painter)
{
    hourhandpen.setColor(Qt::white);
    hourhandpen.setWidth(2.0);//设置小时刻度线为粗黑
    minutehandpen.setColor(Qt::white);
    for(int i=1;i<=60;i++)
    {
        painter->save();
        painter->rotate(6*i);
        if(i%5==0)
        {
            painter->setPen(hourhandpen);
            painter->drawLine(0,-98,0,-82);//原点变了
            painter->drawText(-20,-82,40,40,Qt::AlignHCenter|Qt::AlignTop,QString::number(i/5));
        }
        else
        {
            painter->setPen(minutehandpen);
            painter->drawLine(0,-98,0,-88);
        }
        painter->restore();
    }
}