判断一个多边形是不是凸多边形的js算法代码,Js代码库,德仔网

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【Js】判断一个多边形是不是凸多边形的js算法

作者:泰鑫 / 发布于2017/11/20/ 822

/*
 * 凸多边形的判断，内角和如果不等于（n-2）*180，即不是凸多边形
 */
var concavePolygon = concavePolygon || {
	judge: function (data) {
		var  interiorAngle = 0;
		for (var i = 0, l = data.length; i < l; i++) {
			var vector_1 = {}, vector_2 = {};
			if (i == l -1) {
				vector_1.x = data[l-1].x - data[0].x;
				vector_1.y = data[l-1].y - data[0].y;
				vector_2.x = data[1].x - data[0].x;
				vector_2.y = data[1].y - data[0].y;
			} else if (i == l -2) {
				vector_1.x = data[i].x - data[l -1].x;
				vector_1.y = data[i].y - data[l -1].y;
				vector_2.x = data[0].x - data[l -1].x;
				vector_2.y = data[0].y - data[l -1].y;
			} else{
				vector_1.x = data[i].x - data[i+1].x;
				vector_1.y = data[i].y - data[i+1].y;
				vector_2.x = data[i+2].x - data[i+1].x;
				vector_2.y = data[i+2].y - data[i+1].y;
			}
			interiorAngle += this.vectorAngle(vector_1.x, vector_2.x, vector_1.y, vector_2.y);
		}
		if (isNaN(interiorAngle)) {
			return "repeat";
		} else if (interiorAngle >= ((l-2)*180-1) && interiorAngle <= ((l-2)*180+1)){
			return true
		} else {
			return false;
		}
	},
	vectorAngle: function (x1, x2, y1, y2) {
		var a = x1*x2+y1*y2;
		var b = Math.sqrt(Math.pow(x1, 2) + Math.pow(y1, 2));
		var c = Math.sqrt(Math.pow(x2, 2) + Math.pow(y2, 2));
		var d = b*c;
		var cos = a/d;
		var acos = (Math.acos(cos)/Math.PI)*180;
		return acos;
	
	}
};







html


<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
		<link rel="stylesheet" type="text/css" href="index.css"/>
	</head>
	<body onselectstart="return false">
		<script src="jquery-1.10.2.min.js"></script>
		<canvas id="canvas" width="600" height="500" class="canvas"></canvas>
		<div class="start" id="start">开始绘制</div>
		<div class="checkborder" id="checkborder">切换边</div>
		<div class="checkDeriction" id="checkDeriction">切换方向</div>
		<div class="clear" id="clear">全部清空</div>
		
		<script src="plug.js"></script>
		<script src="judgeConcavePolygon.js"></script>
		<script>
			$("#canvas").drawCoverArrHPP({
				$start : $("#start"),
				$checkDeriction : $("#checkDeriction"),
				$clear : $("#clear"),
				$checkborder : $("#checkborder"),
				$cxt : "canvas",
				$arrPosition : {
					total: 3,
					left: 1
				},
				$callBack: function (data) {
					console.log(data);
					var jude = concavePolygon.judge(data);
					if (!!jude) {
						alert("是凸多边形！");
					} else{
						alert("不是凸多边形！");
					}
				}
			});
		</script>
	</body>
</html>

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