本文实例为大家分享了js+canvas实现鼠标绘制多边形的具体代码，可自动吸附闭合，供大家参考，具体内容如下
效果图：
完整代码：（记得引入jQuery）
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>canvas绘制多边形</title>
<script src="jQuery.js"></script>
</head>
<body>
<style>
canvas {
border: 1px solid #333;
display: block;
}
input {
width: 100px;
margin-left: 200px;
margin-top: 650px;
}
#canvas{
position: absolute;
left: 0;
top: 0;
z-index: 1;
cursor: crosshair;
}
#canvasSave{
position: absolute;
left: 0;
top: 0;
}
</style>
<!--用来和鼠标进行交互操作的canvas-->
<canvas id="canvas" width="1000px" height="600px"></canvas>
<!--存储已生成的点线，避免被清空-->
<canvas id="canvasSave" width="1000px" height="600px"></canvas>
<input id="deleteCanvas" type="button" value="清空选区">
<script>
var can = document.getElementById("canvas");
var ctx = can.getContext('2d');
var canSave = document.getElementById("canvasSave");
var ctxSave = canSave.getContext('2d');
var pointX, pointY;
var pointArr = [];//存放坐标的数组
ctx.strokeStyle = 'rgba(102,168,255,1)';//线条颜色
ctx.lineWidth = 4;//线条粗细
ctxSave.strokeStyle = 'rgba(102,168,255,1)';//线条颜色
ctxSave.lineWidth = 4;//线条粗细
var oIndex = -1;//判断鼠标是否移动到起始点处，-1为否，1为是
$(can).click(function (e) {
if (e.offsetX || e.layerX) {
pointX = e.offsetX == undefined ? e.layerX : e.offsetX;
pointY = e.offsetY == undefined ? e.layerY : e.offsetY;
var piX,piY;
if(oIndex > 0 && pointArr.length > 0){
piX = pointArr[0].x;
piY = pointArr[0].y;
//画点
makearc(ctx, piX, piY, GetRandomNum(2, 2), 0, 180, 'rgba(102,168,255,1)');
pointArr.push({x: piX, y: piY});
canvasSave(pointArr);//保存点线同步到另一个canvas
saveCanvas();//生成画布
}else {
piX = pointX;
piY = pointY;
makearc(ctx, piX, piY, GetRandomNum(2, 2), 0, 180, 'rgba(102,168,255,1)');
pointArr.push({x: piX, y: piY});
canvasSave(pointArr);//保存点线同步到另一个canvas
}
}
});
$(can).mousemove(function (e) {
if (e.offsetX || e.layerX) {
pointX = e.offsetX == undefined ? e.layerX : e.offsetX;
pointY = e.offsetY == undefined ? e.layerY : e.offsetY;
var piX,piY;
ctx.clearRect(0, 0, can.width, can.height);
makearc(ctx, pointX, pointY, GetRandomNum(4, 4), 0, 180, 'rgba(102,168,255,1)');
if (pointArr.length > 0) {
if((pointX > pointArr[0].x-15 && pointX < pointArr[0].x+15) && (pointY > pointArr[0].y-15 && pointY < pointArr[0].y+15)){
if(pointArr.length>1){
piX = pointArr[0].x;
piY = pointArr[0].y;
ctx.clearRect(0, 0, can.width, can.height);
makearc(ctx, piX, piY, GetRandomNum(4, 4), 0, 180, 'rgba(102,168,255,1)');
oIndex = 1;
}
}else {
piX = pointX;
piY = pointY;
oIndex = -1;
}
ctx.beginPath();
ctx.moveTo (pointArr[0].x, pointArr[0].y);
if (pointArr.length > 1){
for (var i = 1; i < pointArr.length; i++){
ctx.lineTo(pointArr[i].x, pointArr[i].y);
}
}
ctx.lineTo(piX, piY);
ctx.fillStyle = 'rgba(161,195,255,1)';//填充颜色
ctx.fill();//填充
ctx.stroke();//绘制
}
}
});
// 存储已生成的点线
function canvasSave(pointArr){
ctxSave.clearRect(0, 0, ctxSave.width, ctxSave.height);
ctxSave.beginPath();
if (pointArr.length > 1){
ctxSave.moveTo (pointArr[0].x, pointArr[0].y);
for (var i = 1; i < pointArr.length; i++){
ctxSave.lineTo(pointArr[i].x, pointArr[i].y);
ctxSave.fillStyle = 'rgba(161,195,255,1)';//填充颜色
//ctxSave.fill();
ctxSave.stroke();//绘制
}
ctxSave.closePath();
}
}
function saveCanvas() {
ctx.clearRect(0, 0, can.width, can.height);
ctxSave.closePath();//结束路径状态，结束当前路径，如果是一个未封闭的图形，会自动将首尾相连封闭起来
ctxSave.fill();//填充
ctxSave.stroke();//绘制
pointArr = [];
}
$('#deleteCanvas').click(function () {
ctx.clearRect(0, 0, can.width, can.height);
ctxSave.clearRect(0, 0, canSave.width, canSave.height);
pointArr = [];
});
function isCanvasBlank(canvas) {
var blank = document.createElement('canvas');//创建一个空canvas对象
blank.width = canvas.width;
blank.height = canvas.height;
return canvas.toDataURL() == blank.toDataURL();//为空 返回true
}
function GetRandomNum(Min, Max) {
var Range = Max - Min;
var Rand = Math.random();
return (Min + Math.round(Rand * Range));
}
function makearc(ctx, x, y, r, s, e, color) {
ctx.clearRect(0, 0, 199, 202);//清空画布
ctx.beginPath();
ctx.fillStyle = color;
ctx.arc(x, y, r, s, e);
ctx.fill();
}
</script>
</body>
</html>以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持编程网。
