Test for object within angle

I've been struggling with this issue for awhile and I know there must be an easy answer but I can't come up with it.

I'm making a top-down space shooter enemy AI. The enemy ship can rotate in any direction. I want to be able to test whether a certain object is within a range of angles relative to the rotation of the ship.

For example if an obstacle is within 0 to 30 degrees (of the front of the ship) I can make the ship turn left (to avoid it) and if there's an obstacle within 0 to -30 degrees I can make the ship turn right.

Using the Angle expression doesn't work because it doesn't account for the rotation of the ship.

And the AngleDiff expression doesn't work because it provides an absolute value and I can't tell whether the object is to the left or right of the ship.

Here's a simple capx that I hope will demonstrate what I'm trying to accomplish.

http://dl.dropbox.com/u/28484936/rotate_issue.capx

Thanks for the help!

Edited by robit_studios - 21 Jan 2012 at 2:51am

this is a sh*tty fix but if you add a +90 to sprite angle so..
anglediff(Sprite.Angle, angle(Sprite.x, Sprite.y, Mouse.x, Mouse.y))

becomes:
anglediff(Sprite.Angle+90, angle(Sprite.x, Sprite.y, Mouse.x, Mouse.y))

Then you can have it so if this value is above 90, then it's on the left.. if it's below 90 it's on the right.

Don't the Sprite conditions 'Is between angles', 'Is within angle' and 'Is clockwise from' help?

You can, just use something like:

Is 30 degrees within angle(Player.X, Player.Y, Target.X, Target.Y)

and

Is clockwise of angle(Player.X, Player.Y, Target.X, Target.Y)

tells you which side it's on.