From d04c41ad80650822be0ff3d18f253a0dbd570116 Mon Sep 17 00:00:00 2001
From: Paramat <paramat@users.noreply.github.com>
Date: Thu, 21 Dec 2017 19:57:42 +0000
Subject: Vector functions: Fix vector.direction() function, improve
 documentation (#6801)

vector.direction() now returns a normalised vector with direction p1 to p2.
---
 builtin/common/vector.lua | 31 +++++-------------------------
 doc/lua_api.txt           | 48 ++++++++++++++++++++++++++++++++---------------
 2 files changed, 38 insertions(+), 41 deletions(-)

diff --git a/builtin/common/vector.lua b/builtin/common/vector.lua
index 0549f9a56..c3d380ed3 100644
--- a/builtin/common/vector.lua
+++ b/builtin/common/vector.lua
@@ -63,34 +63,13 @@ function vector.distance(a, b)
 end
 
 function vector.direction(pos1, pos2)
-	local x_raw = pos2.x - pos1.x
-	local y_raw = pos2.y - pos1.y
-	local z_raw = pos2.z - pos1.z
-	local x_abs = math.abs(x_raw)
-	local y_abs = math.abs(y_raw)
-	local z_abs = math.abs(z_raw)
-	if x_abs >= y_abs and
-	   x_abs >= z_abs then
-		y_raw = y_raw * (1 / x_abs)
-		z_raw = z_raw * (1 / x_abs)
-		x_raw = x_raw / x_abs
-	end
-	if y_abs >= x_abs and
-	   y_abs >= z_abs then
-		x_raw = x_raw * (1 / y_abs)
-		z_raw = z_raw * (1 / y_abs)
-		y_raw = y_raw / y_abs
-	end
-	if z_abs >= y_abs and
-	   z_abs >= x_abs then
-		x_raw = x_raw * (1 / z_abs)
-		y_raw = y_raw * (1 / z_abs)
-		z_raw = z_raw / z_abs
-	end
-	return {x=x_raw, y=y_raw, z=z_raw}
+	return vector.normalize({
+		x = pos2.x - pos1.x,
+		y = pos2.y - pos1.y,
+		z = pos2.z - pos1.z
+	})
 end
 
-
 function vector.add(a, b)
 	if type(b) == "table" then
 		return {x = a.x + b.x,
diff --git a/doc/lua_api.txt b/doc/lua_api.txt
index 7d568b6e1..0637c346b 100644
--- a/doc/lua_api.txt
+++ b/doc/lua_api.txt
@@ -2248,25 +2248,43 @@ The following functions provide escape sequences:
 
 Spatial Vectors
 ---------------
-* `vector.new(a[, b, c])`: returns a vector:
+For the following functions, `v`, `v1`, `v2` are vectors, `p1`, `p2` are positions:
+
+* `vector.new(a[, b, c])`:
+    * Returns a vector.
     * A copy of `a` if `a` is a vector.
-    * `{x = a, y = b, z = c}`, if all `a, b, c` are defined
-* `vector.direction(p1, p2)`: returns a vector
-* `vector.distance(p1, p2)`: returns a number
-* `vector.length(v)`: returns a number
-* `vector.normalize(v)`: returns a vector
-* `vector.floor(v)`: returns a vector, each dimension rounded down
-* `vector.round(v)`: returns a vector, each dimension rounded to nearest int
-* `vector.apply(v, func)`: returns a vector
-* `vector.equals(v1, v2)`: returns a boolean
-* `vector.sort(v1, v2)`: returns minp, maxp vectors of the cuboid defined by v1 and v2
+    * `{x = a, y = b, z = c}`, if all of `a`, `b`, `c` are defined numbers.
+* `vector.direction(p1, p2)`:
+    * Returns a vector of length 1 with direction `p1` to `p2`.
+    * If `p1` and `p2` are identical, returns `{x = 0, y = 0, z = 0}`.
+* `vector.distance(p1, p2)`:
+    * Returns zero or a positive number, the distance between `p1` and `p2`.
+* `vector.length(v)`:
+    * Returns zero or a positive number, the length of vector `v`.
+* `vector.normalize(v)`:
+    * Returns a vector of length 1 with direction of vector `v`.
+    * If `v` has zero length, returns `{x = 0, y = 0, z = 0}`.
+* `vector.floor(v)`:
+    * Returns a vector, each dimension rounded down.
+* `vector.round(v)`:
+    * Returns a vector, each dimension rounded to nearest integer.
+* `vector.apply(v, func)`:
+    * Returns a vector where the function `func` has been applied to each component.
+* `vector.equals(v1, v2)`:
+    * Returns a boolean, `true` if the vectors are identical.
+* `vector.sort(v1, v2)`:
+    * Returns in order minp, maxp vectors of the cuboid defined by `v1`, `v2`.
 
 For the following functions `x` can be either a vector or a number:
 
-* `vector.add(v, x)`: returns a vector
-* `vector.subtract(v, x)`: returns a vector
-* `vector.multiply(v, x)`: returns a scaled vector or Schur product
-* `vector.divide(v, x)`: returns a scaled vector or Schur quotient
+* `vector.add(v, x)`:
+    * Returns a vector.
+* `vector.subtract(v, x)`:
+    * Returns a vector.
+* `vector.multiply(v, x)`:
+    * Returns a scaled vector or Schur product.
+* `vector.divide(v, x)`:
+    * Returns a scaled vector or Schur quotient.
 
 Helper functions
 ----------------
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