FA-10566 / Raster compositing / Open access

Source in clips premultiplied · case 01

Source-in ignores the destination coverage mask.

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

ROOT CAUSE

Source-in ignores the destination coverage mask.

VERIFIED REPAIR

Use the stage contract: Source is premultiplied RGBA. Source-in multiplies every channel by normalized destination alpha.

Unsuccessful approach: Masking only source alpha leaves RGB outside the destination coverage.

Case contract

Source is premultiplied RGBA. Source-in multiplies every channel by normalized destination 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(source, destination_alpha):
    return list(source)
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], 0.5)), [0.25, 0.125, 0, 0.25])
check('fixture 2', solve(*([1, 1, 1, 1], 0)), [0, 0, 0, 0])
check('fixture 3', solve(*([0.5, 0, 0, 0.5], 1)), [0.5, 0, 0, 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 fixture	Actual	Expected	Outcome
fixture 1	`[0.5, 0.25, 0, 0.5]`	`[0.25, 0.125, 0, 0.25]`	Failed
fixture 2	`[1, 1, 1, 1]`	`[0, 0, 0, 0]`	Failed
fixture 3	`[0.5, 0, 0, 0.5]`	`[0.5, 0, 0, 0.5]`	Passed
fixture 4	`[0, 0, 0, 0]`	`[0, 0, 0, 0]`	Passed

SHA-256 / e1a96eac62886f00d8b981b1dba082f04e6a1c59377e074b0098031ddb737a3d

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(source, destination_alpha):
    return source[:3]+[source[3]*destination_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], 0.5)), [0.25, 0.125, 0, 0.25])
check('fixture 2', solve(*([1, 1, 1, 1], 0)), [0, 0, 0, 0])
check('fixture 3', solve(*([0.5, 0, 0, 0.5], 1)), [0.5, 0, 0, 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 fixture	Actual	Expected	Outcome
fixture 1	`[0.5, 0.25, 0, 0.25]`	`[0.25, 0.125, 0, 0.25]`	Failed
fixture 2	`[1, 1, 1, 0]`	`[0, 0, 0, 0]`	Failed
fixture 3	`[0.5, 0, 0, 0.5]`	`[0.5, 0, 0, 0.5]`	Passed
fixture 4	`[0, 0, 0, 0.0]`	`[0, 0, 0, 0]`	Passed

SHA-256 / 0369241ef360bf8ba359930275ac911ef42ccdf49b35387c0c13ef131c976bea

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(source, destination_alpha):
    return [x*destination_alpha for x in source]
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], 0.5)), [0.25, 0.125, 0, 0.25])
check('fixture 2', solve(*([1, 1, 1, 1], 0)), [0, 0, 0, 0])
check('fixture 3', solve(*([0.5, 0, 0, 0.5], 1)), [0.5, 0, 0, 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 fixture	Actual	Expected	Outcome
fixture 1	`[0.25, 0.125, 0.0, 0.25]`	`[0.25, 0.125, 0, 0.25]`	Passed
fixture 2	`[0, 0, 0, 0]`	`[0, 0, 0, 0]`	Passed
fixture 3	`[0.5, 0, 0, 0.5]`	`[0.5, 0, 0, 0.5]`	Passed
fixture 4	`[0.0, 0.0, 0.0, 0.0]`	`[0, 0, 0, 0]`	Passed

SHA-256 / e244345522ddbf7043651f8fa73800c8bb2084b0c48f9c10e1161698359e11da

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 2026-09-29T14:38:40.161891+00:00.

Case digest / 54042867d4afbc7ab002b54aacee74b152f84f279619bebe273952bc3857d4af