Facing cam or not?

Anyone know how to write a routine that will check if an entity is facing the camera or not? Probably would look like;

IsFacingCam(Camera,Entity,FacingRange)

Facing Range would be a degree range that it would consider the front of the entity. Example: 90 would cover the intire front of the entity. It would check if the camera is within a -90 to 90 on the Pitch,Yaw,and Roll relative to the entity in question. I'm not sure if Roll could even be in this.

I hope this makes sense.
Any ideas?

This might be useful:
http://www.blitzbasic.com/codearcs/codearcs.php?code=532

tformpoint I think. transform the object into camera space and check if tformedz is <0 or >0

(experiment)

[edit]: that tells us if the object is behind us, sorry! sleepy...

you'd still need to check the x value aswell cos you could fasr right or left and still out of view.

ps tformpoint sounds the best way though. Also use tformvector to check which way it's facing ie anything anything below abs(1) on the x vector and <0 on the z could tell you the player is facing in the vacinaty of the camera.Based on how you have things setup.

just use the Deltayaw and Deltapitch commands to see how much angle there is for your object to face the other object.

You will need the Blitz3D 1.85 update for these commands though.