modules.lua

-- returns the degrees between (0,0) and pt (note: 0 degrees is 'east')
function angleOfPoint( pt )
   local x, y = pt.x, pt.y
   local radian = math.atan2(y,x)
   local angle = radian*180/math.pi
   if angle < 0 then angle = 360 + angle end
   return angle
end

-- returns the degrees between two points (note: 0 degrees is 'east')
function angleBetweenPoints( a, b )
   local x, y = b.x - a.x, b.y - a.y
   return angleOfPoint( { x=x, y=y } )
end

-- returns the smallest angle between the two angles
-- ie: the difference between the two angles via the shortest distance
function smallestAngleDiff( target, source )
   local a = target - source

   if (a > 180) then
      a = a - 360
   elseif (a < -180) then
      a = a + 360
   end

   return a
end