need Fast function -> Point behind the camera

A fast function to see if a point at X,Y,Z is behind the camera? (outside 180 degree of view)
I was thinking about using vectors, but it could be too slow...

may I ask why you need this?

How can..

TformPoint x,y,z,0,camera
If TformedZ()<0.0 ;then point is behind camera
;do stuff
EndIf

..be too slow?

I need to know if many objects will be inview before placing them on the map (plants) for each frame.
I have my placepoints, and have to decide in wich of them to make the plants appear.
I test the distance from the camera to each placepoint and if the placepoint is behind the camera or not.
Am I wrong? :)

p.s.does tformpoint check takes camera orientation into count?

Calculate a normal for the camera using tformnormal, and then do a dot product between this and each point in the scene you want to check, after subtracting the camera's position from that point.

A dot product is this:
D# = Nx#*Px# + Ny#*Py# + Nz#*Pz#

Then if the result, D#, is positive (I think) the point is in front of the camera.

You may have to normalize the point as well after subtracting the camera position from it. That requires a square root. So hopefully you don't need to do that.

Tformpoint will do it just fine, tformnormal and a dot product could also be done but if you just want to know if it is behind the camera tformpoint will work fine, no need to do a dot product.

Same as Matty said,

do a tformpoint with your X,Y,Z

TFormPoint X,Y,Z,0,camera

and then check the TFormedZ() value, if it is less than cero, then
it means the point is behing the camera.

Paolo.

Thanks to everybody :)