/**
* 计算从x1y1到x2y2的直线,与水平线形成的夹角
* 计算规则为顺时针从左侧0°到与该直线形成的夹角
* @param {Object} x1
* @param {Object} y1
* @param {Object} x2
* @param {Object} y2
*/
function getAngle(x1, y1, x2, y2) {
var x = x1 - x2,
y = y1 - y2;
if (!x && !y) {
return 0;
}
var angle = (180 + Math.atan2(-y, -x) * 180 / Math.PI + 360) % 360;
return 360 - angle;
}
console.log(getAngle(100, 100, 200, 200)); //135