Simple methods for flipping a vector on exactly 1 axis

modules/vec2.lua

@@ -321,6 +321,20 @@ function vec2.to_polar(a)
 	return radius, theta
 end
 
+-- Negate x axis only of vector.
+-- @tparam vec2 a Vector to x-flip.
+-- @treturn vec2 x-flipped vector
+function vec2.flip_x(a)
+	return vec2.new(-a.x, a.y)
+end
+
+-- Negate y axis only of vector.
+-- @tparam vec2 a Vector to y-flip.
+-- @treturn vec2 y-flipped vector
+function vec2.flip_y(a)
+	return vec2.new(a.x, -a.y)
+end
+
 --- Return a formatted string.
 -- @tparam vec2 a Vector to be turned into a string
 -- @treturn string formatted

modules/vec3.lua

@@ -279,6 +279,27 @@ function vec3.component_max(a, b)
 	return new(math.max(a.x, b.x), math.max(a.y, b.y), math.max(a.z, b.z))
 end
 
+-- Negate x axis only of vector.
+-- @tparam vec2 a Vector to x-flip.
+-- @treturn vec2 x-flipped vector
+function vec3.flip_x(a)
+	return vec3.new(-a.x, a.y, a.z)
+end
+
+-- Negate y axis only of vector.
+-- @tparam vec2 a Vector to y-flip.
+-- @treturn vec2 y-flipped vector
+function vec3.flip_y(a)
+	return vec3.new(a.x, -a.y, a.z)
+end
+
+-- Negate z axis only of vector.
+-- @tparam vec2 a Vector to z-flip.
+-- @treturn vec2 z-flipped vector
+function vec3.flip_z(a)
+	return vec3.new(a.x, a.y, -a.z)
+end
+
 --- Return a boolean showing if a table is or is not a vec3.
 -- @tparam vec3 a Vector to be tested
 -- @treturn boolean is_vec3

spec/vec2_spec.lua

@@ -189,6 +189,14 @@ describe("vec2:", function()
 		assert.is.equal("(+0.000,+0.000)", b)
 	end)
 
+	it("flips a 2-vector", function()
+		local a = vec2(1,2)
+		local temp = a:flip_x()
+		assert.is.equal(temp, vec2(-1, 2))
+		temp = temp:flip_y()
+		assert.is.equal(temp, vec2(-1, -2))
+	end)
+
 	-- Do this last, to insulate tests from accidental state contamination
 	it("converts a vec3 to vec2 using the constructor", function()
 		local vec3 = require "modules.vec3"

spec/vec3_spec.lua

@@ -202,4 +202,14 @@ describe("vec3:", function()
 		local b = a:to_string()
 		assert.is.equal("(+0.000,+0.000,+0.000)", b)
 	end)
+
+	it("flips a 3-vector", function()
+		local a = vec3(1,2,3)
+		local temp = a:flip_x()
+		assert.is.equal(temp, vec3(-1, 2, 3))
+		temp = temp:flip_y()
+		assert.is.equal(temp, vec3(-1, -2, 3))
+		temp = temp:flip_z()
+		assert.is.equal(temp, vec3(-1, -2, -3))
+	end)
 end)