Question

In the code below, I want to make sure a line is rotating clockwise in relation to another line. The line I want to go clockwise has angle targetAngle.

var dX = line.start.x - someOtherPoint.x;
var dY = line.start.y - someOtherPoint.y;
var lastAngle = Math.atan2(dY, dX);

var dX = line.start.x - line.end.x;
var dY = line.start.y - line.end.y;
var targetAngle = Math.atan2(dY, dX);

if (targetAngle < lastAngle) {
    // is going counter clockwise
} else {
    // is going clockwise
}

This code works in most cases, but breaks when targetAngle has gone below 0.

Answer 1

Changing this:

if (targetAngle < lastAngle) {

to this:

if (targetAngle < lastAngle && !(targetAngle < 0 && lastAngle > 0)) {

seems to do the trick.