Y ↑
  │  Bevy world ↑                                        LDtk-World ↓ 
  │  (Y increases upward)                           (increases downward)
  │
  │     -32          -16            0            16            32
  │      ┌────────────┬─────────────┬─────────────┬─────────────┐   │
  │  32  │            │             │      L2     │             │-32│
  │      │            │             │  (top-lvl)  │             │   │
  │      │            │             │             │             │   │
  │      ├────────────┼─────────────┼─────────────┼─────────────┤   │
  │  16  │            │     L1      │   L0        │     L3      │-16│
  │      │            │             │             │             │   │
  │      │            │             │   (0,0)     │             │   │
  │      ├────────────┼─────────────O─────────────┼─────────────┤   │
  │   0  │            │             │   L4        │             │ 0 │
  │      │            │             │             │             │   │
  │      │            │             │             │             │   │
  │      ├────────────┴─────────────┴─────────────┴─────────────┤   │
  │ -16  │                        L5                            │ 16│
  │      │                 (bottom-lvl)                         │   │
  │      │                                                      │   │
  │      └──────────────────────────────────────────────────────┘   ↓
  │
  └───────────────────────────────────────────────────────────────► X →
        -32         -16            0            16            32
```

Legend
──────
• Each square = 16×16 tiles.
• **Bevy Y** increases **upward** (↑).
• **LDtk Y** (both world & inside level) increases **downward** (↓).

Coordinate examples
───────────────────
Level L0  (at origin)
  LDtk world anchor (top-left) = (0, -16)
  Top-left corner in Bevy world   = (0, 16)

Level L1  (left of origin)
  LDtk world anchor               = (-16, -16)
  Top-left corner in Bevy world   = (-16, 16)

Level L2  (above origin)
  LDtk world anchor               = (0, -32 )
  Top-left corner in Bevy world   = (0, 32)

Level L3  (right origin)
  LDtk world anchor               = (16, -16)
  Top-left corner in Bevy world   = (16, -16)

Level L4  (below L3)
  LDtk world anchor               = (0, 16)
  Top-left corner in Bevy world   = (0, -16)

Level L5 (below L4, spanning 4 x levels)
  LDtk world anchor               = (-32, 32)
  Top-left corner in Bevy world   = (-32, -32)


Player's world-based gridcoords need to be converted to the internal coordinates for a level (so we can match it with
the cached walls HashMap).
To convert between world and in-level coords:

lX = wX - level_world_x
lY = wY - (-level_world_y - level_height)