In view cone snippet

bool CMyEnt::InViewCone( const Vector &vecSpot, float tolerance ) {

   Vector los = ( vecSpot - GetAbsOrigin() );
   los.z = 0;
   VectorNormalize( los );
   Vector facingDir;
   AngleVectors( GetAbsAngles(), &facingDir );
   float flDot = DotProduct( los, facingDir );

   if ( flDot > tolerance )

return true;

   return false;

}