hi, i want my NPC´s to be intelligent, but at first, i need checking whether they can see you. it works for blocking geometry already. but i want to test if the viewpoint the enemy "looks at" is pointing at me, the player. i have tried something like this to find out the angle:
unfortunately, this algo does not work. can someone point me to the right way? thanks Gammastrahler [edited by - Gammastrahler on June 13, 2002 2:42:47 PM]

You want to dot the vector from the enemy to the player, with the enemies view vector.

Death of one is a tragedy, death of a million is just a statistic.

It would also be easier to store the view range already in terms of the cosine/dot product, i.e -1 to 1. It would avoid the expensive cos call and you wouldn''t have to worry about the absolute value, as the cosine''s domain takes care of the left/right direction problem inherently.

----------------------------------
if (fabs(acos(d)) > 45)
----------------------------------

Also ''acos'' returns a value in radians, so the above line should be something like

if (fabs(acos(d)) > PI/4)

Stephen

Wouldn`t you want a view frustrum type thing.
Similar to the camera in gfx ?
"Just" have a truncated cone, then check if any player poly are within it ?

Bugle4d

How are you partitioning your space?

Regards,
Mathematix.

my engine currently uses no partitioning system (since it is in a very early development stadium).

but i plan to implement a portal engine for my inside areas and something other for my outside areas.

a view frustum for enemies would be a good idea (very accurate, i think). but would it be fast??

thanks
Gammastrahler

I''d just do d > 0.707, i.e. d > sqrt(2.0)/2.0.

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Python_Regious has the best idea. We used the vector from the NPC to the Player, then compared that to the NPC''s current sight cone. ( our cone is a vector for direction that the NPC is facing, and the stored cosine values of the pitch and yaw of the cone). I wrote a function called pointincone, that took the player''s position, and created the vector to the player, did the dot product for the yaw, and b/c this vector is normalized, only had to look at the z value for the pitch.

Like Fruny said, everything in terms of the dot product.