線分交差判定 - Qiita

var judgeIentersected = function(ax, ay, bx, by, cx, cy, dx, dy) { var ta = (cx - dx) * (ay - cy) + (cy - dy) * (cx - ax); var tb = (cx - dx) * (by - cy) + (cy - dy) * (cx - bx); var tc = (ax - bx) * (cy - ay) + (ay - by) * (ax - cx); var td = (ax - bx) * (dy - ay) + (ay - by) * (ax - dx); return tc * td < 0 && ta * tb < 0; // return tc * td <= 0 && ta * tb <= 0; // 端点を含む場合 };