I'm making a top down game where the player moves forwards towards the position of the mouse cursor. As part of the player's movement code, I need to determine a vector that is perpendicular to the player's current facing vector (to implement strafing behavior).
How can I compute the perpendicular vector of a given 2D vector?
I always forget how to do this when I need it so I wrote a couple of extension methods.
public static Vector2 PerpendicularClockwise(this Vector2 vector2) { return new Vector2(vector2.Y, -vector2.X); } public static Vector2 PerpendicularCounterClockwise(this Vector2 vector2) { return new Vector2(-vector2.Y, vector2.X); } And a unit test
[Test] public void Vector2_Perpendicular_Test() { var a = new Vector2(5, -10); var b = a.PerpendicularClockwise(); var c = a.PerpendicularCounterClockwise(); Assert.AreEqual(new Vector2(-10, -5), b); Assert.AreEqual(new Vector2(10, 5), c); } 
To get the 2D vector perpendicular to another 2D vector simply swap the X and Y components, negating the new Y component. So { x, y } becomes { y, -x }.
If 
, then a-perp obtained by a counterclockwise rotation by 90 degrees, i.e., 
See this link :)
