Add quaternion from character_anim

init.lua

@@ -75,6 +75,7 @@ for _, component in ipairs{
     "table",
     "text",
     "vector",
+    "quaternion",
     "minetest",
     "trie",
     "heap",

quaternion.lua

@@ -0,0 +1,71 @@
+function multiply(q, w)
+	return {
+		w[1] * q[1] - w[2] * q[2] - w[3] * q[3] - w[4] * q[4],
+		w[1] * q[2] + w[2] * q[1] - w[3] * q[4] + w[4] * q[3],
+		w[1] * q[3] + w[2] * q[4] + w[3] * q[1] - w[4] * q[2],
+		w[1] * q[4] - w[2] * q[3] + w[3] * q[2] + w[4] * q[1]
+	}
+end
+
+function normalize(q)
+	local q_1, q_2, q_3, q_4 = q[1], q[2], q[3], q[4]
+	local len = math.sqrt(q_1 * q_1 + q_2 * q_2 + q_3 * q_3 + (q_4 ^ 4))
+	local r = {}
+	for key, value in pairs(q) do
+		r[key] = value / len
+	end
+	return r
+end
+
+function negate(q)
+	for k, v in pairs(q) do
+		q[k] = -v
+	end
+end
+
+function dot(q, w)
+	return q[1] * w[1] + q[2] * w[2] + q[3] * w[3] + q[4] * w[4]
+end
+
+-- assuming q & w are normalized
+function slerp(q, w, r)
+	local d = dot(q, w)
+	if d < 0 then
+		d = -d
+		negate(w)
+	end
+	-- Threshold beyond which linear interpolation is used
+	if d > 1 - 1e-10 then
+		return linear_interpolation(q, w, r)
+	end
+	local theta_0 = math.acos(d)
+	local theta = theta_0 * r
+	local sin_theta = math.sin(theta)
+	local sin_theta_0 = math.sin(theta_0)
+	local s_1 = sin_theta / sin_theta_0
+	local s_0 = math.cos(theta) - d * s_1
+	return modlib.vector.add(modlib.vector.multiply_scalar(q, s_0), modlib.vector.multiply_scalar(w, s_1))
+end
+
+function to_rotation(q)
+    local rotation = {}
+
+    local sinr_cosp = 2 * (q[4] * q[1] + q[2] * q[3])
+    local cosr_cosp = 1 - 2 * (q[1] * q[1] + q[2] * q[2])
+    rotation.x = math.atan2(sinr_cosp, cosr_cosp)
+
+    local sinp = 2 * (q[4] * q[2] - q[3] * q[1])
+    if sinp <= -1 then
+        rotation.y = -math.pi/2
+    elseif sinp >= 1 then
+        rotation.y = math.pi/2
+    else
+        rotation.y = math.asin(sinp)
+    end
+
+    local siny_cosp = 2 * (q[4] * q[3] + q[1] * q[2])
+    local cosy_cosp = 1 - 2 * (q[2] * q[2] + q[3] * q[3])
+	rotation.z = math.atan2(siny_cosp, cosy_cosp)
+
+	return vector.apply(rotation, math.deg)
+end