From 02d7604b172c4a16b11ddfa2692eaea5b00aadb6 Mon Sep 17 00:00:00 2001
From: xiejiangzhi <xiejiangzhi@gmail.com>
Date: Wed, 20 Apr 2022 19:13:08 +0800
Subject: [PATCH 1/2] Add vec3.angle_to

---
 modules/vec3.lua   | 5 +++++
 spec/vec3_spec.lua | 6 ++++++
 2 files changed, 11 insertions(+)

diff --git a/modules/vec3.lua b/modules/vec3.lua
index ed8ea05..b466028 100644
--- a/modules/vec3.lua
+++ b/modules/vec3.lua
@@ -318,6 +318,11 @@ 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)
+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
diff --git a/spec/vec3_spec.lua b/spec/vec3_spec.lua
index 8621fee..7db88b5 100644
--- a/spec/vec3_spec.lua
+++ b/spec/vec3_spec.lua
@@ -224,4 +224,10 @@ describe("vec3:", function()
 		temp = temp:flip_z()
 		assert.is.equal(temp, vec3(-1, -2, -3))
 	end)
+
+	-- it("get two 3-vectors angle", function()
+	-- 	local a = vec3(1,2,3)
+	-- 	local b = vec3(3,2,1)
+	-- 	-- assert.is.equal(a:angle_to(b), 1)
+	-- end)
 end)

From 6bc7ec77186db01b5692873437a3d7ea274efa75 Mon Sep 17 00:00:00 2001
From: "jiangzhi.xie" <xiejiangzhi@gmail.com>
Date: Wed, 20 Apr 2022 20:00:28 +0800
Subject: [PATCH 2/2] Add testing code for vec3.angle_to

---
 spec/vec3_spec.lua | 30 +++++++++++++++++++++++++-----
 1 file changed, 25 insertions(+), 5 deletions(-)

diff --git a/spec/vec3_spec.lua b/spec/vec3_spec.lua
index 7db88b5..d620eca 100644
--- a/spec/vec3_spec.lua
+++ b/spec/vec3_spec.lua
@@ -225,9 +225,29 @@ describe("vec3:", function()
 		assert.is.equal(temp, vec3(-1, -2, -3))
 	end)
 
-	-- it("get two 3-vectors angle", function()
-	-- 	local a = vec3(1,2,3)
-	-- 	local b = vec3(3,2,1)
-	-- 	-- assert.is.equal(a:angle_to(b), 1)
-	-- end)
+	it("get two 3-vectors angle", function()
+    local angle_to = function(a, b)
+      local deg = math.deg(a:angle_to(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')
+
+    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')
+
+    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')
+	end)
 end)