Qt坐标变换

//平移
void translate(qreal dx, qreal dy);

//顺时针旋转
void rotate(qreal angle);
//缩放
void scale(qreal sx, qreal sy);
//扭转
void shear(qreal sh, qreal sv);

//保存当前状态
void save();
//恢复上次状态
void restore();
//复位坐标变换
void resetTransform();

PaintPath.pro

QT += core gui

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

TARGET = PaintPath
TEMPLATE = app

SOURCES += main.cpp 
    widget.cpp

HEADERS  += widget.h

main.cpp

#include "widget.h"
#include 

int main(int argc, char *argv[]) {
    QApplication a(argc, argv);

    Widget w;
    w.show();

    return a.exec();
}

widget.h

#ifndef WIDGET_H
#define WIDGET_H

#include 

class Widget : public QWidget {
    Q_OBJECT
public:
    explicit Widget(QWidget *parent = 0);
protected:
    void paintEvent(QPaintEvent *event) Q_DECL_OVERRIDE;
};

#endif // WIDGET_H

widget.cpp

#include "widget.h"
#include 
#include 

Widget::Widget(QWidget *parent) : QWidget(parent) {
    setPalette(QPalette(Qt::white));
    setAutoFillBackground(true);
    resize(600, 300);
}

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
    const   qreal Pi = 3.14159;
    qreal   deg = Pi*72/180;//


    QPoint points[5] = {
        QPoint(R, 0),
        QPoint(R*qCos(deg),     -R*qSin(deg)),
        QPoint(R*qCos(2*deg),   -R*qSin(2*deg)),
        QPoint(R*qCos(3*deg),   -R*qSin(3*deg)),
        QPoint(R*qCos(4*deg),   -R*qSin(4*deg))
    };

    //设置字体
    QFont font;
    font.setPointSize(12);
    font.setBold(true);
    painter.setFont(font);

    //设置画笔
    QPen  pen;
    pen.setWidth(2); //线宽
    pen.setColor(Qt::blue); //划线颜色
    //Qt::NoPen, Qt::SolidLine, Qt::DashLine, Qt::DotLine, Qt::DashDotLine, Qt::DashDotDotLine, Qt::CustomDashLine
    pen.setStyle(Qt::SolidLine);//线的类型，实线、虚线等
    //Qt::FlatCap, Qt::SquareCap, Qt::RoundCap
    pen.setCapStyle(Qt::FlatCap);//线端点样式
    //Qt::MiterJoin, Qt::BevelJoin, Qt::RoundJoin, Qt::SvgMiterJoin
    pen.setJoinStyle(Qt::BevelJoin);//线的连接点样式
    painter.setPen(pen);

    //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");
}