Qt绘制直线箭头

一.使用QPainter绘制

满足条件:

任意角度直线都可绘制箭头
所有箭头同样大小

void MainWindow::paintEvent(QPaintEvent*)
{QPainter painter(this);  // 创建QPainter对象，并指定绘制目标为当前的widgetQLineF line(50,20,500,500);double distanceFromEnd1 = 20;qreal t = (line.length() - distanceFromEnd1) / line.length();QPointF point = line.pointAt(t);//与两端平行点double distanceFromEnd2 = 5;qreal z = (line.length() - distanceFromEnd2) / line.length();QPointF point_center=line.pointAt(z);//中心点qreal slope_line = (line.p2().y() - line.p1().y()) / (line.p2().x() - line.p1().x());  // 计算原直线斜率double slope = -1 / slope_line;  // 计算垂线的斜率double intercept = point.y() - slope * point.x();  // 计算垂线的截距const double m=5;//垂线上下两端距离double arrow1_x=(point.y()+m-intercept)/slope;double arrow2_x=(point.y()-m-intercept)/slope;QPointF arrow1(arrow1_x,slope*arrow1_x+intercept);QPointF arrow2(arrow2_x,slope*arrow2_x+intercept);painter.setRenderHint(QPainter::Antialiasing, true);  // 可选，抗锯齿设置painter.setPen(QPen(Qt::black, 2));  // 设置画笔颜色和宽度painter.drawLine(line);  // 绘制直线painter.setPen(QPen(Qt::green,3));painter.drawLine(arrow1,point_center);painter.drawLine(arrow2,point_center);
}

二.使用QPainterPath绘制

1.如何使用 GraphicsView 和 QGraphicsScene 绘制

创建一个类继承 GraphicsView

graphicsView.h

#ifndef GRAPHICSVIEW_H
#define GRAPHICSVIEW_H
#include <QGraphicsView>
#include <QMouseEvent>
#include <QGraphicsLineItem>
#include <QGraphicsPathItem>
#include <QPainterPath>
#include <QDebug>
#include <QObject>
#include <QPointF>
#include <QGraphicsEllipseItem>class GraphicsView : public QGraphicsView
{
public:GraphicsView(QGraphicsScene *scene, QWidget *parent = nullptr);void setLineData();
private:QGraphicsScene *scene_;
};#endif // GRAPHICSVIEW_H

graphicsview.cpp

#include "graphicsview.h"GraphicsView::GraphicsView(QGraphicsScene *scene,QWidget *parent ) : QGraphicsView(parent),scene_(scene)
{setScene(scene_);setLineData();
}
void GraphicsView::setLineData()
{QLineF line(100,100,600,400);QPen pen(Qt::red,3);scene_->addLine(line,pen);}

主函数中添加私有对象:

private:Ui::MainWindow *ui;GraphicsView *graphics_view;QGraphicsScene *scene;

主函数中调用:

MainWindow::MainWindow(QWidget *parent) :QMainWindow(parent),ui(new Ui::MainWindow)
{ui->setupUi(this);scene = new QGraphicsScene(this);// 创建 GraphicsView 对象并设置场景GraphicsView* graphicsView = new GraphicsView(scene, this);// 添加 GraphicsView 对象为中央部件
//    setCentralWidget(graphicsView);// 将 GraphicsView 添加到主窗口
//    setCentralWidget(graphicsView);setCentralWidget(graphicsView);// 设置场景大小为主窗口的大小QRectF rect(0, 0, width(), height());scene->setSceneRect(rect);// 根据视图大小调整窗口大小adjustSize();}