#ifndef WIDGET_H
#define WIDGET_H
 
#include <QWidget>
 
namespace Ui {
class Widget;
}
 
class Widget : public QWidget
{
 Q_OBJECT
 
protected:
 void paintEvent(QPaintEvent *event);
 
public:
 explicit Widget(QWidget *parent = nullptr);
 ~Widget();
 
private:
 Ui::Widget *ui;
 
};
 
#endif // WIDGET_H

#include "widget.h"
#include "ui_widget.h"
#include <QPainter>
#include <iostream>
 
#include<math.h>
using namespace std;
 
void Widget::paintEvent(QPaintEvent *event)
{
 Q_UNUSED(event)
 QPainter painter(this);//創(chuàng)建QPainter對象
 painter.setRenderHint(QPainter::Antialiasing);//
 painter.setRenderHint(QPainter::TextAntialiasing);//
 //生成五角星的5個頂點的,假設原點在五角星中心
 qreal R = 100; //半徑 //這里說明一下，qreal 在windows 下面是double 在嵌入式中是float類型。
 const qreal Pi = 3.1415926;
 qreal deg = Pi * 72/180;
 QPoint points[5] = {
 QPoint(R,0),
 QPoint(R*cos(deg),-R*sin(deg)),
 QPoint(R*cos(2*deg),-R*sin(2*deg)),
 QPoint(R*cos(3*deg),-R*sin(3*deg)),
 QPoint(R*cos(4*deg),-R*sin(4*deg)),
 };
 
 //設置字體
 QFont font;
 font.setPointSize(12);
 font.setBold(true);
 painter.setFont(font);
 
 
 //設置畫筆
 QPen penLine;
 penLine.setWidth(2);//線寬
 penLine.setColor(Qt::blue); //劃線顏色
 //Qt::NoPen,Qt::SolidLine, Qt::DashLine, Qt::DotLine,Qt::DashDotLine,Qt::DashDotDotLine,Qt::CustomDashLine
 penLine.setStyle(Qt::SolidLine);//線的類型，實線、虛線等
 //Qt::FlatCap, Qt::SquareCap,Qt::RoundCap
 penLine.setCapStyle(Qt::FlatCap);//線端點樣式
 //Qt::MiterJoin,Qt::BevelJoin,Qt::RoundJoin,Qt::SvgMiterJoin
 penLine.setJoinStyle(Qt::BevelJoin);//線的連接點樣式
 painter.setPen(penLine);
 
 //設置畫刷
 QBrush brush;
 brush.setColor(Qt::yellow); //畫刷顏色
 brush.setStyle(Qt::SolidPattern); //畫刷填充樣式
 painter.setBrush(brush); //
 
 //設計繪制五角星的PainterPath，以便重復使用
 QPainterPath starPath;
 starPath.moveTo(points[0]);
 starPath.lineTo(points[2]);
 starPath.lineTo(points[4]);
 starPath.lineTo(points[1]);
 starPath.lineTo(points[3]);
 starPath.closeSubpath(); //閉合路徑，最后一個點與第一個點相連
 
 starPath.addText(points[0],font,"0"); //顯示端點編號
 starPath.addText(points[1],font,"1");
 starPath.addText(points[2],font,"2");
 starPath.addText(points[3],font,"3");
 starPath.addText(points[4],font,"4");
 
 //繪圖
 painter.save(); //保存坐標狀態(tài)
 painter.translate(100,120);
 painter.drawPath(starPath); //畫星星
 painter.drawText(0,0,"S1");
 painter.restore(); //恢復坐標狀態(tài)
 
 painter.translate(300,120); //平移
 painter.scale(0.8,0.8); //縮放
 painter.rotate(90); //順時針旋轉
 painter.drawPath(starPath);//畫星星
 painter.drawText(0,0,"S2");
 
 painter.resetTransform(); //復位所有坐標變換
 painter.translate(500,120); //平移
 painter.rotate(-145); //逆時針旋轉
 painter.drawPath(starPath);//畫星星
 painter.drawText(0,0,"S3");
}
 
Widget::Widget(QWidget *parent) :
 QWidget(parent),
 ui(new Ui::Widget)
{
 ui->setupUi(this);
 setPalette(QPalette(Qt::white)); //設置背景色是白色
 setAutoFillBackground(true); //設置背景自動填充
 resize(600,300); //固定大小
}
 
Widget::~Widget()
{
 delete ui;
}