ref={this.circle}

style={{left, top}}

className=‘text’>RPL10

<span

onMouseDown={(e) => this._mouseDown(e)}

onMouseUp={(e) => this._mouseUp(e)}

className=‘inside_circle’

/>

);

}

_mouseDown(e) {

this.setState({

moveFlag: true

})

this.circle.current.style.left = 50

}

_mouseUp(e) {

if (this.state.moveFlag) {

this.setState({

moveFlag: false

})

}

}

_cleanCanvas(drawNewLine) {

// 清空画布

let canvas = document.querySelector(‘#canvas’);

let ctx = canvas.getContext(‘2d’);

canvas.height = 800;

drawNewLine && drawNewLine(ctx)

}

_drawNewLine(ctx, left, top) {

ctx.moveTo(left, top);

// 4. 绘制直线

ctx.lineTo(401, 401);

// 5. 描边

ctx.stroke();

}

}

export default App;

App.css

*{

margin: 0;

padding: 0;

}

.app{

width: 800px;

height: 800px;

/background-color: red;/

position: relative;

border: 1px solid #000;

}

.circle{

height: 6px;

width: 6px;

border-radius: 50%;

background-color: orange;

position: absolute;

left: 50%;

top: 50%;

transform: translate(-3px);

}

.text{

padding: 0;

margin: 0;

border: 1px solid #999999;

font-weight: bolder;

position: absolute;

display: flex;

justify-content: center;

align-items: center;

z-index: 999;

user-select: none;

}

.inside_circle{

height: 6px;

width: 6px;

border-radius: 50%;

background-color: #00ff18;

position: absolute;

cursor: pointer;

}

版本2.0

================================================================

运行效果：

================================================================

思路：改进了一些地方，通过两直线相交，将起点改为了与DIV的交点。同时终点距离黄色圆圈有一定距离。

============================================================================================================

方法：

1. 两直线相交

2. 相似

React代码：

===================================================================

App.js

---

import ‘./App.css’;

import React from ‘react’

class App extends React.Component {

constructor(props) {

super(props);

this.circle = React.createRef();

this.state = {

left: 0,

top: 0,

moveFlag: false,

orangeX: 401,

orangeY: 404

}

}

componentDidMount() {

document.onmousemove = (e) => {

if (this.state.moveFlag) {

let {pageX, pageY} = e;

// 1. 更改矩形位置

if (this.state.moveFlag) {

this.setState({

left: pageX - 25,

top: pageY - 10

})

}

// 2. 清空画布并绘制新的线

this._cleanCanvas((ctx) => {

// 2.1 生成text和circle

const text = {

getBBox: () => {

return {

x: pageX,

y: pageY,

width: 50,

height: 20

}

}

}

const circle = {

center: {

x: 401,

y: 404

},

radius: 3

}

let res = this._around(text, circle)

this._drawNewLine(ctx, res);

// this._drawNewLine(ctx, pageX, pageY);

});

}

}

}

render() {

const {left, top} = this.state

return (