   Trig headache
  When I put a value into acos/asin, I always get a value -Pi/2 < angle < Pi/2.  But, I want to know how to get an angle 0 < angle < 2*Pi.  Someone help please? 
if(theta < 0.0f)  theta += 2*PI; ;  That really only works for angles in the fourth quadrant.  Angles that are Pi/2 < angle < 3*Pi/2 are still erroneous. ;  You will have to find another way of doing this, not by asin/acos...the reason? the sin and cos functions aren`t inversible in it entire domain (that`s it, [0,2*pi) ). The reason to this is that there are always two angles that have the same sin... for example:sin(pi/6)=0.5sin(5*pi/6)=0.5so, asin(0.5) would be pi/6 or 5*pi/6??for that reason, the image of asin is defined only in 2 quadrants. 