[vec] Add functions to compute angles, minor style fixes.

vec.lua

@@ -10,6 +10,7 @@
 local min, max = math.min, math.max
 local sin, cos = math.sin, math.cos
 local abs = math.abs
+local atan2 = math.atan2
 local sqrt = math.sqrt
 
 local vec = {}
@@ -172,28 +173,32 @@ function vec.dist3(x1,y1,z1, x2,y2,z2)
     return sqrt(dx*dx + dy*dy + dz*dz)
 end
 
---- Rotate point (px,py) around (ox,oy) by the provided
+--- Rotate vector (vx,vy) around (ox,oy) by the provided
 --  sine and cosine.
 --
 --  This function should only be used for (valuable)
 --  optimization purposes.
-function vec.rotatesincos(px,py, sina,cosa, ox,oy)
-    return ox + cosa*px - sina*py,
-           oy + sina*px + cosa*py
+function vec.rotatesincos(vx,vy, sina,cosa, ox,oy)
+    return ox + cosa*vx - sina*vy,
+           oy + sina*vx + cosa*vy
 end
 
---- Rotate point (px,py) around (ox,oy) about rot radians.
-function vec.rotatepoint(px,py, rot, ox,oy)
+--- Rotate vector (vx,vy) around (ox,oy) about rot radians.
+function vec.rotate(vx,vy, rot, ox,oy)
     ox = ox or 0
     oy = oy or 0
 
     local sina,cosa = sin(rot),cos(rot)
 
     -- vec.rotatesincos(px,py, sina,cosa, ox,oy)
-    return ox + cosa*px - sina*py,
-           oy + sina*px + cosa*py
+    return ox + cosa*vx - sina*vy,
+           oy + sina*vx + cosa*vy
 end
 
+function vec.angle(x,y) return atan2(y,x) end
+
+function vec.angleto(x1,y1, x2,y2) return atan2(y1,x1) - atan2(y2,x2) end
+
 --- Transform world coordinates to screen coordinates.
 --
 -- @param x (number) World coordinate X.