(breaking) vec3: Rename angle_to -> angle_between

modules/vec2.lua

@@ -257,18 +257,14 @@ end
 
 --- Unsigned angle between two vectors.
 -- Directionless and thus commutative.
+-- Input vectors must be non-zero.
 -- @tparam vec2 a Vector
 -- @tparam vec2 b Vector
 -- @treturn number angle in [0, pi]
 function vec2.angle_between(a, b)
 	if b then
-		if vec2.is_vec2(a) then
-			return acos(a:dot(b) / (a:len() * b:len()))
-		end
-
-		return acos(vec3.dot(a, b) / (vec3.len(a) * vec3.len(b)))
+		return acos(a:dot(b) / (a:len() * b:len()))
 	end
-
 	return 0
 end
 

modules/vec3.lua

@@ -4,6 +4,7 @@
 local modules = (...):gsub('%.[^%.]+$', '') .. "."
 local precond = require(modules .. "_private_precond")
 local private = require(modules .. "_private_utils")
+local acos    = math.acos
 local sqrt    = math.sqrt
 local cos     = math.cos
 local sin     = math.sin
@@ -330,9 +331,20 @@ function vec3.flip_z(a)
 	return vec3.new(a.x, a.y, -a.z)
 end
 
-function vec3.angle_to(a, b)
-	local v = a:normalize():dot(b:normalize())
-	return math.acos(v)
+-- No angle_to because that requires defining an axis of rotation. Instead you
+-- likely want to convert both into vec2 and use vec2.angle_to.
+
+--- Unsigned angle between two vectors.
+-- Directionless and thus commutative.
+-- Input vectors must be non-zero.
+-- @tparam vec3 a Vector
+-- @tparam vec3 b Vector
+-- @treturn number angle in [0, pi]
+function vec3.angle_between(a, b)
+	if b then
+		return acos(a:dot(b) / (a:len() * b:len()))
+	end
+	return 0
 end
 
 --- Return a boolean showing if a table is or is not a vec3.

spec/vec3_spec.lua

@@ -232,30 +232,33 @@ describe("vec3:", function()
 		assert.is.equal(temp, vec3(-1, -2, -3))
 	end)
 
-	it("get two 3-vectors angle", function()
-		local angle_to = function(a, b)
-			local deg = math.deg(a:angle_to(b))
+	it("gets angle between two 3-vectors", function()
+		local angle_between = function(a, b)
+			local deg = math.deg(a:angle_between(b))
 			return string.format('%.2f', deg)
 		end
 
 		local a = vec3(1,2,3)
-		assert.is.equal(angle_to(a, vec3(3, 2, 1)), '44.42')
-		assert.is.equal(angle_to(a, vec3(0, 10, 0)), '57.69')
-		assert.is.equal(angle_to(a, vec3(0, -12, -10)), '157.51')
+		assert.is.equal(angle_between(a, a), '0.00')
+		assert.is.equal(angle_between(a, vec3(3, 2, 1)), '44.42')
+		assert.is.equal(angle_between(a, vec3(0, 10, 0)), '57.69')
+		assert.is.equal(angle_between(a, vec3(0, -12, -10)), '157.51')
 
 		a = vec3.unit_z
-		assert.is.equal(angle_to(a, vec3(0, 10, 0)), '90.00')
-		assert.is.equal(angle_to(a, vec3(-123, 10, 0)), '90.00')
-		assert.is.equal(angle_to(a, vec3(-10, 0, 10)), '45.00')
-		assert.is.equal(angle_to(a, vec3(-10, 0, -10)), '135.00')
-		assert.is.equal(angle_to(a, vec3(0, -10, -10)), '135.00')
-		assert.is.equal(angle_to(a, vec3(0, 0, -10)), '180.00')
-		assert.is.equal(angle_to(a, vec3(0, 0, 100)), '0.00')
+		assert.is.equal(angle_between(a, a), '0.00')
+		assert.is.equal(angle_between(a, vec3(0, 10, 0)), '90.00')
+		assert.is.equal(angle_between(a, vec3(-123, 10, 0)), '90.00')
+		assert.is.equal(angle_between(a, vec3(-10, 0, 10)), '45.00')
+		assert.is.equal(angle_between(a, vec3(-10, 0, -10)), '135.00')
+		assert.is.equal(angle_between(a, vec3(0, -10, -10)), '135.00')
+		assert.is.equal(angle_between(a, vec3(0, 0, -10)), '180.00')
+		assert.is.equal(angle_between(a, vec3(0, 0, 100)), '0.00')
 
 		a = vec3(100, 100, 0)
-		assert.is.equal(angle_to(a, vec3(0, 0, 100)), '90.00')
-		assert.is.equal(angle_to(a, vec3(0, 0, -100)), '90.00')
-		assert.is.equal(angle_to(a, vec3(-10, -10, 0)), '180.00')
-		assert.is.equal(angle_to(a, vec3.unit_z), '90.00')
+		assert.is.equal(angle_between(a, a), '0.00')
+		assert.is.equal(angle_between(a, vec3(0, 0, 100)), '90.00')
+		assert.is.equal(angle_between(a, vec3(0, 0, -100)), '90.00')
+		assert.is.equal(angle_between(a, vec3(-10, -10, 0)), '180.00')
+		assert.is.equal(angle_between(a, vec3.unit_z), '90.00')
 	end)
 end)