我对您的代码进行了一些更改：
做
var col一个全局变量在鼠标上方保存当前矩形的颜色：
color:col当您在
shapes阵列中绘制形状时ctx.beginPath()，每个矩形都需要。您还可以为每个矩形设置笔触的颜色：ctx.strokeStyle = shapes[i].color;
观察：您可以使用strokeRect（）方法代替rect()和stroke()
在代码中，我标记了进行更改的那些点。阅读评论。
jQuery(document).ready(function($) {
//Canvas
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
//Variables
var canvasOffset = $("#canvas").offset();
var canvasx = canvasOffset.left;
var canvasy = canvasOffset.top;
var last_mousex = 0;
var last_mousey = 0;
var mousex = 0;
var mousey = 0;
var mousedown = false;
var shapes = [];
var width;
var height;
// make var col a global variable
var col = "black";
//Mousedown
$(canvas).on('mousedown', function(e) {
last_mousex = parseInt(e.clientX - canvasx);
last_mousey = parseInt(e.clientY - canvasy);
mousedown = true;
});
//Mouseup
$(canvas).on('mouseup', function(e) {
const lastPos = {
lastMouseX: last_mousex,
lastMouseY: last_mousey,
rectWidth: width,
rectHeight: height,
// save the color of the rect
color:col
};
shapes.push(lastPos);
mousedown = false;
});
//Mousemove
$(canvas).on('mousemove', function(e) {
mousex = parseInt(e.clientX - canvasx);
mousey = parseInt(e.clientY - canvasy);
if (mousedown) {
ctx.clearRect(0, 0, canvas.width, canvas.height);
width = mousex - last_mousex;
height = mousey - last_mousey;
col = $(".color").val();
if (shapes.length > 0) {
for (var i in shapes) {
// for every shape in the shapes array beginPath
ctx.beginPath();
//set the color of the stroke
ctx.strokeStyle = shapes[i].color;
//draw the rect
ctx.rect(shapes[i].lastMouseX, shapes[i].lastMouseY, shapes[i].rectWidth, shapes[i].rectHeight);
ctx.stroke();
}
}
//for the new rect beginPath
ctx.beginPath();
ctx.rect(last_mousex, last_mousey, width, height);
ctx.strokeStyle = col;
ctx.lineWidth = 10;
ctx.stroke();
}
/*
$("#canvas").mousedown(function(e) {
handleMouseDown(e);
});
$("#canvas").mousemove(function(e) {
handleMouseMove(e);
});
$("#canvas").mouseup(function(e) {
handleMouseUp(e);
});*/
//Output
$('#output').html('current: ' + mousex + ', ' + mousey + '<br/>last: ' + last_mousex + ', ' + last_mousey + '<br/>mousedown: ' + mousedown);
});
});.color {
border: 1px solid black;
font-family: 'Times New Roman', Times, serif;
font-size: 40px;
}
#canvas {
cursor: crosshair;
border: 1px solid #000000;
background-image: url("kroki2v3.png");
background-repeat: no-repeat;
margin: 0;
padding: 0;
}
#output {
font-family: 'Times New Roman', Times, serif;
font-size: 40px;
}<html>
<head>
<meta charset="utf-8" />
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
</head>
<body>
<input type="text" maxlength="50" class="color" required />
<div id="container" style="display: none;"><img src="kroki2v3.png" id="img01" alt="" style="display: none;"></div>
<canvas id="canvas" width="3200" height="1400"></canvas>
<div id="output"></div>
</body>
</html>
最好的代码更改，尤其是第二次更改。谢谢您的答复。我也想知道如何创建可拖动的矩形。画布使用限制了可拖动属性。如果我可以为创建的矩形创建ID或类，这将更加容易。
您无法为矩形分配类别或ID，但是由于矩形是保存在数组中的，因此可以使用索引号，例如
shapes[2]可以在画布上拖动矩形，但是在绘制过程中会发生-就像绘图一样mousedown，mousemove，mouseup事件。您将需要一种在绘制和拖动之间进行切换的方法。但这是一个不同的问题。