   Angle between two points
  Hi! Ok, i''m trying to figure out the angle from a 2D Point (x1, y1) to another (x2, y2). Basically, the two points are two different objects (an enemy and a player) and I want to make the enemy face the player. However, here''s the catch. I can do this with a divide and a multiply by a trig function (angle = (opp/adj) * tanInv). But this needs to be super fast. Anyone know of a better way to do this? Thanks! 
  does it really need to be super fast?  It sounds like you''ve got a great solution already.  Why don''t you implement that, get your game working, and then profile and optimize the parts that really need it. ;  Well, I''m doing this on the GameBoy Advance, so a divide is really out of the question. I was thinking I could use a lookup table, but the dx and dy (opposite and adjacent sides) can be anything. ;  how about something very simple //    x B    ^//   /  |//  /   |  //    A /    |    Dir//x--------------->////  B on left side of dir, turn left//////   ^//   |//   |//    A   |  Dir//x--------------->// \//  \//   \//    \//x B//////  B on right side of dir, turn right  if you can compute the quadrant, that would be even better, like for example if (dx > 0){    if (dx > dy)    {   if (dx > (dy << 1)) // (dy * 2)   {   }   else   {    }    }}ect...you can probably generate a bitfield, with all the signs and the comparisons (or signs of substracted numbers), and get a quadrant like that, or even more accurate. 