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javascript - 确定在 HTML 画布中绘制的直线和曲线之间的距离

问题描述

我有一个 HTML、CSS 和 JavaScript 程序，可以在其中从初始点（Mousedown 事件）曲线（Mousemove 事件）和鼠标点击抬起时的直线（MouseUp 事件）绘制一条直线。

现在我的问题是找到曲线的距离以及两个不同标签中的直线。

我的代码在下面

var canvas = document.querySelector('#paint');
var ctx = canvas.getContext('2d');

var sketch = document.querySelector('#sketch');
var sketch_style = getComputedStyle(sketch);
canvas.width = parseInt(sketch_style.getPropertyValue('width'));
canvas.height = parseInt(sketch_style.getPropertyValue('height'));

var mouse = {
  x: 0,
  y: 0
};

var last_mouse = {
  x: 0,
  y: 0
};

/* Mouse Capturing Work */
canvas.addEventListener('mousemove', function(e) {
  last_mouse.x = mouse.x;
  last_mouse.y = mouse.y;

  mouse.x = e.pageX - this.offsetLeft;
  mouse.y = e.pageY - this.offsetTop;
}, false);


/* Drawing on Paint App */
ctx.lineWidth = 5;
ctx.lineJoin = 'round';
ctx.lineCap = 'round';
ctx.strokeStyle = 'black';
canvas.addEventListener('mousedown', function(e) {
  initialPoint = {
    x: mouse.x,
    y: mouse.y
  }
  canvas.addEventListener('mousemove', onPaint, false);
}, false);

canvas.addEventListener('mouseup', function() {
  drawStraightLine()
  canvas.removeEventListener('mousemove', onPaint, false);
}, false);

var onPaint = function() {
  ctx.beginPath();
  ctx.moveTo(last_mouse.x, last_mouse.y);
  ctx.lineTo(mouse.x, mouse.y);
  ctx.strokeStyle = "#000000";
  ctx.closePath();
  ctx.stroke();
};

let initialPoint
const drawStraightLine = function() {
  ctx.beginPath();
  ctx.moveTo(initialPoint.x, initialPoint.y);
  ctx.lineTo(mouse.x, mouse.y);
  ctx.strokeStyle = "#FF000077";
  ctx.stroke();
}
html,
body {
  width: 80%;
  height: 50%;
}

#sketch {
  border: 10px solid gray;
  height: 100%;
}
<div id="sketch">
  <canvas id="paint"></canvas>
  <script src="1.js"></script>
</div>
<label id="StraightLineDistance"></label>
<label id="CurvedLineDistance"></label>

标签： javascripthtmlhtml5-canvas

解决方案

JavaScript 文件

const canvas = document.querySelector('#paint');
const ctx = canvas.getContext('2d');

const sketch = document.querySelector('#sketch');
const sketch_style = getComputedStyle(sketch);
canvas.width = parseInt(sketch_style.getPropertyValue('width'));
canvas.height = parseInt(sketch_style.getPropertyValue('height'));
var pathLength = 0;
var distance = 0;

const mouse = {x: 0,  y: 0};
const last_mouse = {x: 0,  y: 0};
const initialPoint  = {x: 0,  y: 0};

function distanceBetween(A, B) {
const dx = B.x - A.x; 
const dy = B.y - A.y; 
return (dx * dx + dy * dy) ** 0.5;
}


/* Drawing on Paint App */
ctx.lineWidth = 5;
ctx.lineJoin = 'round';
ctx.lineCap = 'round';
ctx.strokeStyle = 'black';
canvas.addEventListener('mousedown', function(e) {
initialPoint.x = mouse.x = e.pageX - this.offsetLeft;
initialPoint.y = mouse.y = e.pageY - this.offsetTop;
pathLength = 0;
canvas.addEventListener('mousemove', onPaint);
}, false);

canvas.addEventListener('mouseup', function() {
drawStraightLine()
canvas.removeEventListener('mousemove', onPaint);
}, false);

function displayLengths() {
StraightLineDistance.textContent = "Distance: " + distance.toFixed(0) + "px";
CurvedLineDistance.textContent = "Traveled: " + pathLength.toFixed(0) + "px";

} 

function onPaint(e) {
last_mouse.x = mouse.x;
last_mouse.y = mouse.y;

mouse.x = e.pageX - this.offsetLeft;
mouse.y = e.pageY - this.offsetTop;

ctx.strokeStyle = "#000000";
ctx.beginPath();
ctx.lineTo(last_mouse.x, last_mouse.y);
ctx.lineTo(mouse.x, mouse.y);
ctx.stroke();

pathLength += distanceBetween(last_mouse, mouse);
distance = distanceBetween(initialPoint, mouse);
displayLengths();
};


function drawStraightLine() {
ctx.strokeStyle = "#FF000077";
ctx.beginPath();
ctx.lineTo(initialPoint.x, initialPoint.y);
ctx.lineTo(mouse.x, mouse.y);
ctx.stroke();

distance = distanceBetween(initialPoint, mouse);
displayLengths();  
}

HTML 文件 

<link rel="stylesheet" href="1.css"/>
</head>

<body>
<div id="sketch">
<canvas id="paint"></canvas>
<script src="1.js"></script>
</div>
<label id="StraightLineDistance"></label><br/>
<label id="CurvedLineDistance"></label><br/>
<label id="Index"></label>
</body>
</html>

我的新疑问是如何在标签 id="Index" 中显示（距离/路径长度）比率的实时值

我试过使用 Index.textContent = (distance/pathLength).toFixed(0); 但这在输出中显示了 1 及其常量。如果我能得到帮助，我会很高兴

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