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I'm working on a small maze puzzle game and I'm trying to add a compass to make it somewhat easier for the player to find their way around the maze. The problem is: I'm using XNA's draw method to rotate the arrow and I don't really know how to get it to rotate properly. What I need it to do is point towards the exit from the player's position, but I'm not sure how I can do that.

So does anyone know how I can do this? Is there a better way to do it?

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up vote 9 down vote accepted

The secret is atan2:

Vector2 exitPosition = whatever;
Vector2 currentPosition = whatever;

Vector2 direction = exitPosition - currentPosition;
float angle = (float)Math.Atan2(direction.Y, direction.X);

atan2 (MSDN) gives you the angle of a vector, with the positive X axis being at an angle of zero, and moving in the positive direction towards the positive Y axis (which is π/2). Simply pass this as the rotation parameter to SpriteBatch.Draw (MSDN).

Make sure your compass needle texture is pointed the correct way for an angle of zero (ie: to the left), or add an appropriate angular offset in your code. Set the origin parameter of the SpriteBatch.Draw call to the pivot point of your needle texture.

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