Add from_speed_yaw to vector helpers

builtin/common/vector.lua

@@ -143,4 +143,13 @@ function vector.get_yaw(pos1, pos2)
 	return math.atan2(dx, dz)
 end
 
+function vector.from_speed_yaw(speed, yaw)
+	if speed == 0 then
+		return {x=0, y=0, z=0}
+	end
+	yaw = yaw + math.pi / 2
+	local x = math.cos(yaw) * speed
+	local z = math.sin(yaw) * speed
+	return {x=x, y=0, z=z}
+end
 

doc/lua_api.txt

@@ -1585,6 +1585,9 @@ Vector helpers
 * 'vector.interpolate(p1, p2, factor)': returns a vector
 * `vector.get_yaw(p1, p2)`: returns a number
     *Gets the yaw angle to point at p2 from p1
+* `vector.from_speed_yaw(speed, yaw)`
+    * Gets a vector representing the given speed and yaw direction.
+      (y component will always be 0)
 
 For the following functions `x` can be either a vector or a number: