BGE local position not respecting rotation

Question

I am playing around in the game engine and I am moving this cube around with this code:

import bge
from mathutils import Matrix, Euler
from math import radians
obj = bge.logic.getCurrentScene().objects["cube"]
property = bge.logic.getCurrentScene().objects["Empty"].get("movement")
move = 0.0
if property == 1: move = [1, 0.1]
elif property == 2: move = [1, -0.1]
elif property == 3: move = (obj.worldOrientation).to_euler(); move.rotate_axis("Z", radians(2.0))
elif property == 4: move = (obj.worldOrientation).to_euler(); move.rotate_axis("Z", radians(-2.0))
if move != 0.0 and property in (1, 2):
    obj.localPosition[move[0]] += move[1]
elif move != 0.0:
    print(move)
    obj.worldOrientation = move

Where the property is just a int representing which way to go or rotate. The movement is applied to the localPosition so I would think that this would respect the rotation, but it doesn't and this is the result:

So how do I get it to always move in the local +- Y direction?

Answer 1

localPosition is actually the position relative to the objects parent (for the most part, see below). If the cube has no parent, it will be the same as worldPosition.

To move forward along the local Y axis:

obj.applyMovement((0, 0.1, 0), True)

---

Irrelevant localPosition quirk

localPosition isn't truly relative to the parent. It's more like... relative to the parent modified by its world position when initially parented (or something like that). So if your parent isn't at the origin when hiting control+P, the result might be kind of weird. Intended behavior? No idea.