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FA-86666 / Procedural level generation constraints / Open access

Wall autotile bitmask: Floors look like isolated pillars · case 01

Floor cells receive the isolated-wall sprite.

Verified by executionVariant 1 · 8 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Non-wall cells are given mask 0, which is the isolated wall piece.

VERIFIED REPAIR

Restore `row.append(-1)` at the non-wall marker step.

Unsuccessful approach: Only plain floor gets -1; doors and chasms still look like pillars.

Case contract

For each '#' cell the mask sums N=1, E=2, S=4, W=8 for 4-neighbours that are '#' (row 0 is north). Out-of-bounds neighbours count as walls when same_oob. Non-wall cells get -1. Returns rows of integers.

Why this case matters

Procedural generators silently emit unplayable or unfair levels when a single constraint check uses the wrong boundary, axis, neighborhood or update order; the defect is visible in exact generated geometry.

1 / The failure

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(grid, same_oob):
    h = len(grid)
    w = len(grid[0])
    out = []
    for r in range(h):
        row = []
        for c in range(w):
            if grid[r][c] != '#':
                row.append(0)
                continue
            m = 0
            for bit, (dr, dc) in ((1, (-1, 0)), (2, (0, 1)), (4, (1, 0)), (8, (0, -1))):
                rr, cc = r + dr, c + dc
                if 0 <= rr < h and 0 <= cc < w:
                    if grid[rr][cc] == '#':
                        m |= bit
                elif same_oob:
                    m |= bit
            row.append(m)
        out.append(row)
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[('door next to wall #1', [['#D'], False], [[0, -1]]),
  ('regression non-wall marker #1', [['.#D', '#.~'], True], [[-1, 1, -1], [12, -1, -1]]),
  ('regression non-wall marker #2',
   [['~###', '##~.', 'D~~.', '#D#.', '#..#'], True],
   [[-1, 7, 11, 11], [10, 9, -1, -1], [-1, -1, -1, -1], [12, -1, 0, -1], [13, -1, -1, 6]]),
  ('regression non-wall marker #3', [['##D', '..#', '##D'], True], [[11, 9, -1], [-1, -1, 2], [14, 12, -1]]),
  ('regression non-wall marker #4', [['####D'], False], [[2, 10, 10, 8, -1]]),
  ('vertical wall pair #1', [['#', '#'], False], [[4], [1]]),
  ('lone wall at edge #1', [['#'], True], [[15]]),
  ('control #1', [['#', '#', '#'], False], [[4], [5], [1]])],
 [('door next to wall #1', [['#D'], False], [[0, -1]]),
  ('regression non-wall marker #1',
   [['~###', '##~.', 'D~~.', '#D#.', '#..#'], True],
   [[-1, 7, 11, 11], [10, 9, -1, -1], [-1, -1, -1, -1], [12, -1, 0, -1], [13, -1, -1, 6]]),
  ('regression non-wall marker #2', [['##D', '..#', '##D'], True], [[11, 9, -1], [-1, -1, 2], [14, 12, -1]]),
  ('regression non-wall marker #3', [['####D'], False], [[2, 10, 10, 8, -1]]),
  ('regression non-wall marker #4', [['D~#', '#~.'], False], [[-1, -1, 0], [0, -1, -1]]),
  ('vertical wall pair #1', [['#', '#'], False], [[4], [1]]),
  ('lone wall at edge #1', [['#'], True], [[15]]),
  ('control #1', [['#', '#', '#'], False], [[4], [5], [1]])],
 [('door next to wall #1', [['#D'], False], [[0, -1]]),
  ('regression non-wall marker #1', [['####D'], False], [[2, 10, 10, 8, -1]]),
  ('regression non-wall marker #2', [['D~#', '#~.'], False], [[-1, -1, 0], [0, -1, -1]]),
  ('regression non-wall marker #3',
   [['##.D', '.D#~', '##..', '#.#~', '~D.#'], True],
   [[11, 9, -1, -1], [-1, -1, 0, -1], [14, 8, -1, -1], [9, -1, 0, -1], [-1, -1, -1, 6]]),
  ('regression non-wall marker #4',
   [['#..D.', '.##.#', '..##D', 'D.#.D'], False],
   [[0, -1, -1, -1, -1], [-1, 2, 12, -1, 0], [-1, -1, 7, 8, -1], [-1, -1, 1, -1, -1]]),
  ('vertical wall pair #1', [['#', '#'], False], [[4], [1]]),
  ('lone wall at edge #1', [['#'], True], [[15]]),
  ('control #1', [['#', '#', '#'], False], [[4], [5], [1]])],
 [('door next to wall #1', [['#D'], False], [[0, -1]]),
  ('regression non-wall marker #1',
   [['##.D', '.D#~', '##..', '#.#~', '~D.#'], True],
   [[11, 9, -1, -1], [-1, -1, 0, -1], [14, 8, -1, -1], [9, -1, 0, -1], [-1, -1, -1, 6]]),
  ('regression non-wall marker #2',
   [['#..D.', '.##.#', '..##D', 'D.#.D'], False],
   [[0, -1, -1, -1, -1], [-1, 2, 12, -1, 0], [-1, -1, 7, 8, -1], [-1, -1, 1, -1, -1]]),
  ('regression non-wall marker #3', [['~#', '.~', '.#'], True], [[-1, 3], [-1, -1], [-1, 6]]),
  ('regression non-wall marker #4', [['~', '~'], True], [[-1], [-1]]),
  ('vertical wall pair #1', [['#', '#'], False], [[4], [1]]),
  ('lone wall at edge #1', [['#'], True], [[15]]),
  ('control #1', [['#'], False], [[0]])],
 [('door next to wall #1', [['#D'], False], [[0, -1]]),
  ('regression non-wall marker #1', [['~#', '.~', '.#'], True], [[-1, 3], [-1, -1], [-1, 6]]),
  ('regression non-wall marker #2', [['~', '~'], True], [[-1], [-1]]),
  ('regression non-wall marker #3', [['~.#', '##D'], True], [[-1, -1, 3], [14, 12, -1]]),
  ('regression non-wall marker #4',
   [['#~~', '..D', '~#.', 'D.D'], False],
   [[0, -1, -1], [-1, -1, -1], [-1, 0, -1], [-1, -1, -1]]),
  ('vertical wall pair #1', [['#', '#'], False], [[4], [1]]),
  ('lone wall at edge #1', [['#'], True], [[15]]),
  ('control #1', [['##'], False], [[2, 8]])]]
for label, args, expected in cases[N-1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
door next to wall #1[[0, 0]][[0, -1]]Failed
regression non-wall marker #1[[0, 1, 0], [12, 0, 0]][[-1, 1, -1], [12, -1, -1]]Failed
regression non-wall marker #2[[0, 7, 11, 11], [10, 9, 0, 0], [0, 0, 0, 0], [12, 0, 0, 0], [13, 0, 0, 6]][[-1, 7, 11, 11], [10, 9, -1, -1], [-1, -1, -1, -1], [12, -1, 0, -1], [13, -1, -1, 6]]Failed
regression non-wall marker #3[[11, 9, 0], [0, 0, 2], [14, 12, 0]][[11, 9, -1], [-1, -1, 2], [14, 12, -1]]Failed
regression non-wall marker #4[[2, 10, 10, 8, 0]][[2, 10, 10, 8, -1]]Failed
vertical wall pair #1[[4], [1]][[4], [1]]Passed
lone wall at edge #1[[15]][[15]]Passed
control #1[[4], [5], [1]][[4], [5], [1]]Passed

SHA-256 / 879e0712de1e4365ed8ff5dcf00199021a90af8203e454866f55d24cc4e07716

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(grid, same_oob):
    h = len(grid)
    w = len(grid[0])
    out = []
    for r in range(h):
        row = []
        for c in range(w):
            if grid[r][c] != '#':
                row.append(-1 if grid[r][c] == '.' else 0)
                continue
            m = 0
            for bit, (dr, dc) in ((1, (-1, 0)), (2, (0, 1)), (4, (1, 0)), (8, (0, -1))):
                rr, cc = r + dr, c + dc
                if 0 <= rr < h and 0 <= cc < w:
                    if grid[rr][cc] == '#':
                        m |= bit
                elif same_oob:
                    m |= bit
            row.append(m)
        out.append(row)
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[('door next to wall #1', [['#D'], False], [[0, -1]]),
  ('regression non-wall marker #1', [['.#D', '#.~'], True], [[-1, 1, -1], [12, -1, -1]]),
  ('regression non-wall marker #2',
   [['~###', '##~.', 'D~~.', '#D#.', '#..#'], True],
   [[-1, 7, 11, 11], [10, 9, -1, -1], [-1, -1, -1, -1], [12, -1, 0, -1], [13, -1, -1, 6]]),
  ('regression non-wall marker #3', [['##D', '..#', '##D'], True], [[11, 9, -1], [-1, -1, 2], [14, 12, -1]]),
  ('regression non-wall marker #4', [['####D'], False], [[2, 10, 10, 8, -1]]),
  ('vertical wall pair #1', [['#', '#'], False], [[4], [1]]),
  ('lone wall at edge #1', [['#'], True], [[15]]),
  ('control #1', [['#', '#', '#'], False], [[4], [5], [1]])],
 [('door next to wall #1', [['#D'], False], [[0, -1]]),
  ('regression non-wall marker #1',
   [['~###', '##~.', 'D~~.', '#D#.', '#..#'], True],
   [[-1, 7, 11, 11], [10, 9, -1, -1], [-1, -1, -1, -1], [12, -1, 0, -1], [13, -1, -1, 6]]),
  ('regression non-wall marker #2', [['##D', '..#', '##D'], True], [[11, 9, -1], [-1, -1, 2], [14, 12, -1]]),
  ('regression non-wall marker #3', [['####D'], False], [[2, 10, 10, 8, -1]]),
  ('regression non-wall marker #4', [['D~#', '#~.'], False], [[-1, -1, 0], [0, -1, -1]]),
  ('vertical wall pair #1', [['#', '#'], False], [[4], [1]]),
  ('lone wall at edge #1', [['#'], True], [[15]]),
  ('control #1', [['#', '#', '#'], False], [[4], [5], [1]])],
 [('door next to wall #1', [['#D'], False], [[0, -1]]),
  ('regression non-wall marker #1', [['####D'], False], [[2, 10, 10, 8, -1]]),
  ('regression non-wall marker #2', [['D~#', '#~.'], False], [[-1, -1, 0], [0, -1, -1]]),
  ('regression non-wall marker #3',
   [['##.D', '.D#~', '##..', '#.#~', '~D.#'], True],
   [[11, 9, -1, -1], [-1, -1, 0, -1], [14, 8, -1, -1], [9, -1, 0, -1], [-1, -1, -1, 6]]),
  ('regression non-wall marker #4',
   [['#..D.', '.##.#', '..##D', 'D.#.D'], False],
   [[0, -1, -1, -1, -1], [-1, 2, 12, -1, 0], [-1, -1, 7, 8, -1], [-1, -1, 1, -1, -1]]),
  ('vertical wall pair #1', [['#', '#'], False], [[4], [1]]),
  ('lone wall at edge #1', [['#'], True], [[15]]),
  ('control #1', [['#', '#', '#'], False], [[4], [5], [1]])],
 [('door next to wall #1', [['#D'], False], [[0, -1]]),
  ('regression non-wall marker #1',
   [['##.D', '.D#~', '##..', '#.#~', '~D.#'], True],
   [[11, 9, -1, -1], [-1, -1, 0, -1], [14, 8, -1, -1], [9, -1, 0, -1], [-1, -1, -1, 6]]),
  ('regression non-wall marker #2',
   [['#..D.', '.##.#', '..##D', 'D.#.D'], False],
   [[0, -1, -1, -1, -1], [-1, 2, 12, -1, 0], [-1, -1, 7, 8, -1], [-1, -1, 1, -1, -1]]),
  ('regression non-wall marker #3', [['~#', '.~', '.#'], True], [[-1, 3], [-1, -1], [-1, 6]]),
  ('regression non-wall marker #4', [['~', '~'], True], [[-1], [-1]]),
  ('vertical wall pair #1', [['#', '#'], False], [[4], [1]]),
  ('lone wall at edge #1', [['#'], True], [[15]]),
  ('control #1', [['#'], False], [[0]])],
 [('door next to wall #1', [['#D'], False], [[0, -1]]),
  ('regression non-wall marker #1', [['~#', '.~', '.#'], True], [[-1, 3], [-1, -1], [-1, 6]]),
  ('regression non-wall marker #2', [['~', '~'], True], [[-1], [-1]]),
  ('regression non-wall marker #3', [['~.#', '##D'], True], [[-1, -1, 3], [14, 12, -1]]),
  ('regression non-wall marker #4',
   [['#~~', '..D', '~#.', 'D.D'], False],
   [[0, -1, -1], [-1, -1, -1], [-1, 0, -1], [-1, -1, -1]]),
  ('vertical wall pair #1', [['#', '#'], False], [[4], [1]]),
  ('lone wall at edge #1', [['#'], True], [[15]]),
  ('control #1', [['##'], False], [[2, 8]])]]
for label, args, expected in cases[N-1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
door next to wall #1[[0, 0]][[0, -1]]Failed
regression non-wall marker #1[[-1, 1, 0], [12, -1, 0]][[-1, 1, -1], [12, -1, -1]]Failed
regression non-wall marker #2[[0, 7, 11, 11], [10, 9, 0, -1], [0, 0, 0, -1], [12, 0, 0, -1], [13, -1, -1, 6]][[-1, 7, 11, 11], [10, 9, -1, -1], [-1, -1, -1, -1], [12, -1, 0, -1], [13, -1, -1, 6]]Failed
regression non-wall marker #3[[11, 9, 0], [-1, -1, 2], [14, 12, 0]][[11, 9, -1], [-1, -1, 2], [14, 12, -1]]Failed
regression non-wall marker #4[[2, 10, 10, 8, 0]][[2, 10, 10, 8, -1]]Failed
vertical wall pair #1[[4], [1]][[4], [1]]Passed
lone wall at edge #1[[15]][[15]]Passed
control #1[[4], [5], [1]][[4], [5], [1]]Passed

SHA-256 / 44da59e2c510fbb96c0a8e12fd8244701e54e15980613528d0c41faebc6393dd

3 / The verified repair

Exit 0
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(grid, same_oob):
    h = len(grid)
    w = len(grid[0])
    out = []
    for r in range(h):
        row = []
        for c in range(w):
            if grid[r][c] != '#':
                row.append(-1)
                continue
            m = 0
            for bit, (dr, dc) in ((1, (-1, 0)), (2, (0, 1)), (4, (1, 0)), (8, (0, -1))):
                rr, cc = r + dr, c + dc
                if 0 <= rr < h and 0 <= cc < w:
                    if grid[rr][cc] == '#':
                        m |= bit
                elif same_oob:
                    m |= bit
            row.append(m)
        out.append(row)
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[('door next to wall #1', [['#D'], False], [[0, -1]]),
  ('regression non-wall marker #1', [['.#D', '#.~'], True], [[-1, 1, -1], [12, -1, -1]]),
  ('regression non-wall marker #2',
   [['~###', '##~.', 'D~~.', '#D#.', '#..#'], True],
   [[-1, 7, 11, 11], [10, 9, -1, -1], [-1, -1, -1, -1], [12, -1, 0, -1], [13, -1, -1, 6]]),
  ('regression non-wall marker #3', [['##D', '..#', '##D'], True], [[11, 9, -1], [-1, -1, 2], [14, 12, -1]]),
  ('regression non-wall marker #4', [['####D'], False], [[2, 10, 10, 8, -1]]),
  ('vertical wall pair #1', [['#', '#'], False], [[4], [1]]),
  ('lone wall at edge #1', [['#'], True], [[15]]),
  ('control #1', [['#', '#', '#'], False], [[4], [5], [1]])],
 [('door next to wall #1', [['#D'], False], [[0, -1]]),
  ('regression non-wall marker #1',
   [['~###', '##~.', 'D~~.', '#D#.', '#..#'], True],
   [[-1, 7, 11, 11], [10, 9, -1, -1], [-1, -1, -1, -1], [12, -1, 0, -1], [13, -1, -1, 6]]),
  ('regression non-wall marker #2', [['##D', '..#', '##D'], True], [[11, 9, -1], [-1, -1, 2], [14, 12, -1]]),
  ('regression non-wall marker #3', [['####D'], False], [[2, 10, 10, 8, -1]]),
  ('regression non-wall marker #4', [['D~#', '#~.'], False], [[-1, -1, 0], [0, -1, -1]]),
  ('vertical wall pair #1', [['#', '#'], False], [[4], [1]]),
  ('lone wall at edge #1', [['#'], True], [[15]]),
  ('control #1', [['#', '#', '#'], False], [[4], [5], [1]])],
 [('door next to wall #1', [['#D'], False], [[0, -1]]),
  ('regression non-wall marker #1', [['####D'], False], [[2, 10, 10, 8, -1]]),
  ('regression non-wall marker #2', [['D~#', '#~.'], False], [[-1, -1, 0], [0, -1, -1]]),
  ('regression non-wall marker #3',
   [['##.D', '.D#~', '##..', '#.#~', '~D.#'], True],
   [[11, 9, -1, -1], [-1, -1, 0, -1], [14, 8, -1, -1], [9, -1, 0, -1], [-1, -1, -1, 6]]),
  ('regression non-wall marker #4',
   [['#..D.', '.##.#', '..##D', 'D.#.D'], False],
   [[0, -1, -1, -1, -1], [-1, 2, 12, -1, 0], [-1, -1, 7, 8, -1], [-1, -1, 1, -1, -1]]),
  ('vertical wall pair #1', [['#', '#'], False], [[4], [1]]),
  ('lone wall at edge #1', [['#'], True], [[15]]),
  ('control #1', [['#', '#', '#'], False], [[4], [5], [1]])],
 [('door next to wall #1', [['#D'], False], [[0, -1]]),
  ('regression non-wall marker #1',
   [['##.D', '.D#~', '##..', '#.#~', '~D.#'], True],
   [[11, 9, -1, -1], [-1, -1, 0, -1], [14, 8, -1, -1], [9, -1, 0, -1], [-1, -1, -1, 6]]),
  ('regression non-wall marker #2',
   [['#..D.', '.##.#', '..##D', 'D.#.D'], False],
   [[0, -1, -1, -1, -1], [-1, 2, 12, -1, 0], [-1, -1, 7, 8, -1], [-1, -1, 1, -1, -1]]),
  ('regression non-wall marker #3', [['~#', '.~', '.#'], True], [[-1, 3], [-1, -1], [-1, 6]]),
  ('regression non-wall marker #4', [['~', '~'], True], [[-1], [-1]]),
  ('vertical wall pair #1', [['#', '#'], False], [[4], [1]]),
  ('lone wall at edge #1', [['#'], True], [[15]]),
  ('control #1', [['#'], False], [[0]])],
 [('door next to wall #1', [['#D'], False], [[0, -1]]),
  ('regression non-wall marker #1', [['~#', '.~', '.#'], True], [[-1, 3], [-1, -1], [-1, 6]]),
  ('regression non-wall marker #2', [['~', '~'], True], [[-1], [-1]]),
  ('regression non-wall marker #3', [['~.#', '##D'], True], [[-1, -1, 3], [14, 12, -1]]),
  ('regression non-wall marker #4',
   [['#~~', '..D', '~#.', 'D.D'], False],
   [[0, -1, -1], [-1, -1, -1], [-1, 0, -1], [-1, -1, -1]]),
  ('vertical wall pair #1', [['#', '#'], False], [[4], [1]]),
  ('lone wall at edge #1', [['#'], True], [[15]]),
  ('control #1', [['##'], False], [[2, 8]])]]
for label, args, expected in cases[N-1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
door next to wall #1[[0, -1]][[0, -1]]Passed
regression non-wall marker #1[[-1, 1, -1], [12, -1, -1]][[-1, 1, -1], [12, -1, -1]]Passed
regression non-wall marker #2[[-1, 7, 11, 11], [10, 9, -1, -1], [-1, -1, -1, -1], [12, -1, 0, -1], [13, -1, -1, 6]][[-1, 7, 11, 11], [10, 9, -1, -1], [-1, -1, -1, -1], [12, -1, 0, -1], [13, -1, -1, 6]]Passed
regression non-wall marker #3[[11, 9, -1], [-1, -1, 2], [14, 12, -1]][[11, 9, -1], [-1, -1, 2], [14, 12, -1]]Passed
regression non-wall marker #4[[2, 10, 10, 8, -1]][[2, 10, 10, 8, -1]]Passed
vertical wall pair #1[[4], [1]][[4], [1]]Passed
lone wall at edge #1[[15]][[15]]Passed
control #1[[4], [5], [1]][[4], [5], [1]]Passed

SHA-256 / fde6de4680f1aa9a457df5aa618482357671b5b588f8c99dab29737db2bf8f9e

Verification & scope

Deterministic toy contract stipulated for this model; integer or exact arithmetic only, not a reproduction of any specific game engine. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:50:51.541943+00:00.

Case digest / 29a7eec874f875a16f065e912ea43a58073434d4f112f373567890a157ef743a