Mandatory Tile Alphabet

Purpose

The mandatory map alphabet defines the only symbols accepted before bonus map extensions are considered. In the mandatory build, that rule is exact because the shared bonus tile helper is linked as a no-op compatibility layer.

Mandatory alphabet

Seven symbols define the mandatory map language

Before bonus extensions, validation accepts only floor, wall, one player orientation marker, and explicit void/space cells used around irregular maps. In the mandatory build, the shared bonus tile helper is a no-op, so this alphabet stays exact.

0

Empty floor

traversable cell, no wall render, reachable by player and BFS

1

Solid wall

blocks DDA, collision, BFS traversal, and renders as textured wall

' '

Void / padding

outside-map cell; if BFS reaches it, closure validation fails

N

North spawn

dir(0,-1), plane(+fov,0), then treated as floor

S

South spawn

dir(0,+1), plane(-fov,0), then treated as floor

E

East spawn

dir(+1,0), plane(0,+fov), then treated as floor

W

West spawn

dir(-1,0), plane(0,-fov), then treated as floor

Any other character

validate_chars() rejects immediately.

error

01

behavior by subsystem

Each symbol has a clear role in BFS, collision, and DDA rendering.

Symbol	BFS	Collision	DDA render
0	traversable	free	floor / ceiling
1	solid stop	blocked	hit -> texture
N/S/E/W	spawn start	free (= 0)	floor / ceiling (= 0)
' '	leak -> reject	outside map	must not be reached

02

mandatory vs bonus

Mandatory alphabet stays strict; bonus symbols are accepted only when the bonus-aware helper is replaced by the real bonus implementation.

mandatory alphabet = { 0, 1, N, S, E, W, ' ' }
unknown character  = validation error
bonus extension    = bonus_is_valid_map_char(...)

✓

post-validation invariant

Every cell belongs to the accepted mandatory alphabet, so BFS closure can run safely.

Accepted Symbols

• 0 for empty floor
• 1 for solid wall
• N, S, E, W for the single player spawn and initial orientation
• space for padded or out-of-map cells

Any unknown symbol is rejected by map character validation.

Notes

Spawn symbols are used to initialize player position and camera orientation. The grid still stores them as N/S/E/W, but movement, BFS traversal, and rendering treat them as open floor-like cells.