FAILURE MAP
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FA-10561 / Raster compositing / Open access

Destination out preserves uncovered · case 01

The erased coverage is retained instead of its complement.

Verified by executionVariant 1 · 4 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The erased coverage is retained instead of its complement.

VERIFIED REPAIR

Use the stage contract: Destination is premultiplied RGBA. Destination-out retains each channel times one minus normalized source alpha.

Unsuccessful approach: Erasing only alpha leaves invalid color in transparent pixels.

Case contract

Destination is premultiplied RGBA. Destination-out retains each channel times one minus normalized source alpha.

Why this case matters

A deterministic software graphics stage with explicit channel and coordinate conventions; no hardware, device profile or API behavior is inferred.

1 / The failure

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(destination, source_alpha):
    return [x*source_alpha for x in destination]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('fixture 1', solve(*([0.5, 0.25, 0, 0.5], 0.25)), [0.375, 0.1875, 0, 0.375])
check('fixture 2', solve(*([1, 1, 1, 1], 1)), [0, 0, 0, 0])
check('fixture 3', solve(*([0.5, 0.5, 0.5, 0.5], 0)), [0.5, 0.5, 0.5, 0.5])
check('fixture 4', solve(*([0, 0, 0, 0], 0.5)), [0, 0, 0, 0])
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
fixture 1[0.125, 0.0625, 0.0, 0.125][0.375, 0.1875, 0, 0.375]Failed
fixture 2[1, 1, 1, 1][0, 0, 0, 0]Failed
fixture 3[0.0, 0.0, 0.0, 0.0][0.5, 0.5, 0.5, 0.5]Failed
fixture 4[0.0, 0.0, 0.0, 0.0][0, 0, 0, 0]Passed

SHA-256 / 773d62655acf00b0c44cb3eaec31c03676536d1835bb934779081367f02eda43

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(destination, source_alpha):
    return destination[:3]+[destination[3]*(1-source_alpha)]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('fixture 1', solve(*([0.5, 0.25, 0, 0.5], 0.25)), [0.375, 0.1875, 0, 0.375])
check('fixture 2', solve(*([1, 1, 1, 1], 1)), [0, 0, 0, 0])
check('fixture 3', solve(*([0.5, 0.5, 0.5, 0.5], 0)), [0.5, 0.5, 0.5, 0.5])
check('fixture 4', solve(*([0, 0, 0, 0], 0.5)), [0, 0, 0, 0])
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
fixture 1[0.5, 0.25, 0, 0.375][0.375, 0.1875, 0, 0.375]Failed
fixture 2[1, 1, 1, 0][0, 0, 0, 0]Failed
fixture 3[0.5, 0.5, 0.5, 0.5][0.5, 0.5, 0.5, 0.5]Passed
fixture 4[0, 0, 0, 0.0][0, 0, 0, 0]Passed

SHA-256 / 768874e7e3fa234c2c11f419deadb306df82be702c1ea7e71edb18dad4340f35

3 / The verified repair

Exit 0
"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(destination, source_alpha):
    return [x*(1-source_alpha) for x in destination]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('fixture 1', solve(*([0.5, 0.25, 0, 0.5], 0.25)), [0.375, 0.1875, 0, 0.375])
check('fixture 2', solve(*([1, 1, 1, 1], 1)), [0, 0, 0, 0])
check('fixture 3', solve(*([0.5, 0.5, 0.5, 0.5], 0)), [0.5, 0.5, 0.5, 0.5])
check('fixture 4', solve(*([0, 0, 0, 0], 0.5)), [0, 0, 0, 0])
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
fixture 1[0.375, 0.1875, 0.0, 0.375][0.375, 0.1875, 0, 0.375]Passed
fixture 2[0, 0, 0, 0][0, 0, 0, 0]Passed
fixture 3[0.5, 0.5, 0.5, 0.5][0.5, 0.5, 0.5, 0.5]Passed
fixture 4[0.0, 0.0, 0.0, 0.0][0, 0, 0, 0]Passed

SHA-256 / 0517756e6b7fc6bfa557b69f5553dd98a1fa8c68b72c79f690b2d7a78ce51888

Verification & scope

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 2026-09-29T14:38:40.046031+00:00.

Case digest / 8650396d4d41281b550d68e5e76f23f98bdffb1f3f290f69df50392abf8197b2