Qt5.9画五角星的方法

#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);//创建QPainter对象
 painter.setRenderHint(QPainter::Antialiasing);//
 painter.setRenderHint(QPainter::TextAntialiasing);//
 //生成五角星的5个顶点的,假设原点在五角星中心
 qreal R = 100; //半径 //这里说明一下，qreal 在windows 下面是double 在嵌入式中是float类型。
 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)),
 };
 
 //设置字体
 QFont font;
 font.setPointSize(12);
 font.setBold(true);
 painter.setFont(font);
 
 
 //设置画笔
 QPen penLine;
 penLine.setWidth(2);//线宽
 penLine.setColor(Qt::blue); //划线颜色
 //Qt::NoPen,Qt::SolidLine, Qt::DashLine, Qt::DotLine,Qt::DashDotLine,Qt::DashDotDotLine,Qt::CustomDashLine
 penLine.setStyle(Qt::SolidLine);//线的类型，实线、虚线等
 //Qt::FlatCap, Qt::SquareCap,Qt::RoundCap
 penLine.setCapStyle(Qt::FlatCap);//线端点样式
 //Qt::MiterJoin,Qt::BevelJoin,Qt::RoundJoin,Qt::SvgMiterJoin
 penLine.setJoinStyle(Qt::BevelJoin);//线的连接点样式
 painter.setPen(penLine);
 
 //设置画刷
 QBrush brush;
 brush.setColor(Qt::yellow); //画刷颜色
 brush.setStyle(Qt::SolidPattern); //画刷填充样式
 painter.setBrush(brush); //
 
 //设计绘制五角星的PainterPath，以便重复使用
 QPainterPath starPath;
 starPath.moveTo(points[0]);
 starPath.lineTo(points[2]);
 starPath.lineTo(points[4]);
 starPath.lineTo(points[1]);
 starPath.lineTo(points[3]);
 starPath.closeSubpath(); //闭合路径，最后一个点与第一个点相连
 
 starPath.addText(points[0],font,"0"); //显示端点编号
 starPath.addText(points[1],font,"1");
 starPath.addText(points[2],font,"2");
 starPath.addText(points[3],font,"3");
 starPath.addText(points[4],font,"4");
 
 //绘图
 painter.save(); //保存坐标状态
 painter.translate(100,120);
 painter.drawPath(starPath); //画星星
 painter.drawText(0,0,"S1");
 painter.restore(); //恢复坐标状态
 
 painter.translate(300,120); //平移
 painter.scale(0.8,0.8); //缩放
 painter.rotate(90); //顺时针旋转
 painter.drawPath(starPath);//画星星
 painter.drawText(0,0,"S2");
 
 painter.resetTransform(); //复位所有坐标变换
 painter.translate(500,120); //平移
 painter.rotate(-145); //逆时针旋转
 painter.drawPath(starPath);//画星星
 painter.drawText(0,0,"S3");
}
 
Widget::Widget(QWidget *parent) :
 QWidget(parent),
 ui(new Ui::Widget)
{
 ui->setupUi(this);
 setPalette(QPalette(Qt::white)); //设置背景色是白色
 setAutoFillBackground(true); //设置背景自动填充
 resize(600,300); //固定大小
}
 
Widget::~Widget()
{
 delete ui;
}