From ddb80f48e6a3f7d9b98aa45b6feeb461db3d0c6a Mon Sep 17 00:00:00 2001
From: mcc <andi.m.mcclure@gmail.com>
Date: Sun, 3 May 2020 13:36:26 -0400
Subject: [PATCH] Compatibility note for 1.0 release and PR#48 test

---
 README.md          |  2 +-
 spec/mat4_spec.lua | 26 ++++++++++++++++++++++++++
 spec/quat_spec.lua | 14 ++++++++++++++
 3 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/README.md b/README.md
index 15a5503..92c1d53 100644
--- a/README.md
+++ b/README.md
@@ -15,4 +15,4 @@ Clone the repository and require it, or if you prefer luarocks: `$ luarocks inst
 
 # Versions
 
-This library has a major compatibility break at version 1.0. Up to version 0.10, composition a*b means "apply b, then a" for quaternions and "apply a, then b" for matrices. Starting with version 1.0, the two are consistent and matrix a*b means "apply b, then a".
+This library has a major compatibility break at version 1.0. Up to version 0.10, composition a*b means "apply b, then a" for quaternions and "apply a, then b" for matrices. Now as of version 1.0, the two are consistent and matrix a*b means "apply b, then a".
diff --git a/spec/mat4_spec.lua b/spec/mat4_spec.lua
index eecee4a..5473fcd 100644
--- a/spec/mat4_spec.lua
+++ b/spec/mat4_spec.lua
@@ -184,6 +184,32 @@ describe("mat4:", function()
 		assert.is.equal(c[4], d[4])
 	end)
 
+	it("verifies mat4 composition order", function()
+		local a = mat4 {
+			1, 5, 9,  13,
+			2, 6, 10, 14,
+			3, 7, 11, 15,
+			4, 8, 12, 16
+		}
+		local b = mat4 {
+			2,  3,  5,  7,
+			11, 13, 17, 19,
+			23, 29, 31, 37,
+			41, 43, 47, 53
+		}
+		local c = mat4():mul(a, b)
+		local d = a * b
+
+		local v = { 10, 20, 30, 40 }
+
+		local cv = c * v
+		local abv = a*(b*v)
+
+		assert.is.equal(cv.x, abv.x) -- Verify (a*b)*v == a*(b*v)
+		assert.is.equal(cv.y, abv.y)
+		assert.is.equal(cv.z, abv.z)
+	end)
+
 	it("scales a matrix", function()
 		local a = mat4():scale(mat4(), vec3(5, 5, 5))
 		assert.is.equal(5, a[1])
diff --git a/spec/quat_spec.lua b/spec/quat_spec.lua
index 9867dc8..a85297b 100644
--- a/spec/quat_spec.lua
+++ b/spec/quat_spec.lua
@@ -1,6 +1,7 @@
 local quat  = require "modules.quat"
 local vec3  = require "modules.vec3"
 local utils = require "modules.utils"
+local constants = require "modules.constants"
 
 describe("quat:", function()
 	it("creates an identity quaternion", function()
@@ -125,6 +126,19 @@ describe("quat:", function()
 		assert.is.equal(b, c)
 	end)
 
+	it("verifies quat composition order", function()
+		local a = quat(2, 3, 4, 1):normalize() -- Only the normal quaternions represent rotations
+		local b = quat(3, 6, 9, 1):normalize()
+		local c = a * b
+
+		local v = vec3(3, 4, 5)
+
+		local cv = c * v
+		local abv = a * (b * v)
+
+		assert.is_true((abv - cv):len() < 1e-07) -- Verify (a*b)*v == a*(b*v) within an epsilon
+	end)
+
 	it("multiplies a quaternion by an exponent of 0", function()
 		local a = quat(2, 3, 4, 1):normalize()
 		local e = 0