我是 HTML5 中画布的新学习者，目前正在尝试为孩子们制作一个简单的画线项目。我将背景图像插入画布中，并尝试提出一种徒手画线的方法，但没有结果。有人可以帮我修复下面的代码吗？之前谢谢大家。
<!DOCTYPE HTML>
<html>
<script type="text/javascript">
var canvas, ctx, flag = false,
prevX = 0,
currX = 0,
prevY = 0,
currY = 0,
dot_flag = false;
var x = "black",
y = 2;
function init() {
canvas = document.getElementById('can');
ctx = canvas.getContext("2d");
w = canvas.width;
h = canvas.height;
canvas.addEventListener("mousemove", function (e) {
findxy('move', e)
}, false);
canvas.addEventListener("mousedown", function (e) {
findxy('down', e)
}, false);
canvas.addEventListener("mouseup", function (e) {
findxy('up', e)
}, false);
canvas.addEventListener("mouseout", function (e) {
findxy('out', …