Casting rays for enemy sight

anarkavre · Post by **anarkavre** » Wed Mar 17, 2004 10:32 pm

How would you go about casting rays for enemy sight. I thought about using an array of lines using line3f. Though does anyone have an example of the math involved in doing this.

thesmileman · Post by **thesmileman** » Thu Mar 18, 2004 4:17 am

Possibly with getRayFromScreenCoordinates()

Look here http://irrlicht.sourceforge.net/docu/cl ... er.html#a3

Caecus · Post by **Caecus** » Fri Mar 19, 2004 1:29 am

Actaully what you want is scene::ISceneCollisionManager::getCollisionPoint() which can be found on the same page of the docs that smileman provided a link to.

As far as the math behind it... thats not quite as easy. You going to have to find one of the more math-types to explain it. The simplest idea I have of is to cast a ray (line) from the enemy and testing them against a representation of the player. Obviously this only checks whats directly in front of him. Now you could extend this idea to use an array of lines created using nested for loops simply change the angle of the ray slightly... I'm not sure if casting 4x4 or 10x10 rays for every enemy is very ideal though...

This same basic idea is actaully used in regular collision detection schemes as well... check out the game dev article Pool Hall Physics.. It talks about collisions between two moving objects of different size using rays.

WickedImp · Post by **WickedImp** » Fri Mar 19, 2004 8:36 am

The idea of casting 'rays' for collision detection is not bad at all. But I think if you 'raytrace' so many lines it will be a performance problem.

Here is what I have in mind from the good old quake-engine:

Every player (real persons and bots) have a FOV (i.e. 90°) you first should check if the target (i.e the real player) is in the FOV by getting the calculated degree difference between the view direction of your bot (in this case it is called self) and your target. if it is withing 90° then you can cast a ray directly from the eye of self to the eye of target. If this ray collides with something else in between than you cannot see the target.

Maybe this can be improved by casting rays to all edges of the bounding box of target. If one or more rays only collide with the bbox than you can partially see the target. This could also be used to say that self cannot exactly identify target if he only gets two positive rays

Hope this helps...

Serg Nechaeff · Post by **Serg Nechaeff** » Fri Mar 19, 2004 4:28 pm

also work only with enemies within a cartain distance

anarkavre · Post by **anarkavre** » Fri Mar 19, 2004 9:41 pm

How would I set the fov for a animated scene node, attach a camera as a child to it and set the fov?

Mercior · Post by **Mercior** » Sat Mar 20, 2004 7:35 am

no the fov would be a value you store with your npc's - then you cast the ray between the player and the NPC, check if it doesnt collide and check that the line is within the NPC's field of view (their current angle +- 30 degrees or so)