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FA-51591 / Raster clipping / Open access

Liang barsky parametric rect: left plane sign · case 01

The left boundary distance has the wrong sign, so segments starting inside acquire a spurious entering parameter.

Verified by executionVariant 1 · 13 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The left boundary distance has the wrong sign, so segments starting inside acquire a spurious entering parameter.

THE FAILURE

The left boundary distance has the wrong sign, so segments starting inside acquire a spurious entering parameter.

Unsuccessful approach: Taking the absolute distance fixes interior starts but reverses the parameter for segments starting left of the rectangle.

Case contract

Each command is [x0,y0,x1,y1,rect] with integer coordinates and an inclusive integer rectangle [left,top,right,bottom] that is first intersected with the pixel-center raster [0,size-1]x[0,size-1]. An empty rectangle returns None. Liang-Barsky tests left, right, top and bottom inequalities with exact rational parameters: parallel segments outside a boundary are rejected, points on a boundary are inside, entering parameters raise t0 and leaving parameters lower t1. The result is [t0,t1] as exact rational strings or None.

Why this case matters

Raster clipping decides which pixels a primitive may touch; a single wrong clip decision writes outside the target or scissor, or silently drops visible coverage.

1 / The failure

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json
from fractions import Fraction
N = 1
observations = []
def solve(commands, size):
    out=[]
    for x0,y0,x1,y1,rect in commands:
        l,t,r,b=max(rect[0],0),max(rect[1],0),min(rect[2],size-1),min(rect[3],size-1)
        if l>r or t>b:
            out.append(None)
            continue
        dx,dy=x1-x0,y1-y0
        t0,t1=Fraction(0),Fraction(1)
        ok=True
        for p,q in ((-dx,l-x0),(dx,r-x0),(-dy,y0-t),(dy,b-y0)):
            if p==0:
                if q<0: ok=False
            else:
                u=Fraction(q,p)
                if p<0:
                    if u>t1: ok=False
                    elif u>t0: t0=u
                else:
                    if u<t0: ok=False
                    elif u<t1: t1=u
        out.append([str(t0),str(t1)] if ok else None)
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
if N == 1:
    check('explicit case 0', solve([[-2, 1, 7, 3, [0, 0, 6, 6]]], 6), [['2/9', '7/9']])
    check('explicit case 1', solve([[1, 1, 11, 1, [0, 0, 11, 11]]], 6), [['0', '2/5']])
    check('explicit case 2', solve([[0, 0, 1, 1, [3, 3, 2, 5]]], 6), [None])
    check('explicit case 3', solve([[0, 2, 5, 2, [0, 2, 5, 2]]], 6), [['0', '1']])
    check('explicit case 4', solve([[0, 0, 5, 0, [0, 0, 5, 5]]], 6), [['0', '1']])
    check('explicit case 5', solve([[0, 2, 0, 2, [0, 0, 5, 5]]], 6), [['0', '1']])
    check('explicit case 6', solve([[-4, -1, 4, 7, [0, 0, 5, 5]]], 6), [['1/2', '3/4']])
    check('explicit case 7', solve([[1, 1, 3, 1, [0, 0, 5, 5]]], 6), [['0', '1']])
    check('explicit case 8', solve([[-1, 1, 2, 1, [0, 0, 5, 5]]], 6), [['1/3', '1']])
    check('explicit case 9', solve([[1, 2, 1, 10, [0, 0, 5, 5]]], 6), [['0', '3/8']])
    check('explicit case 10', solve([[2, -3, 5, 5, [1, 1, 4, 6]]], 6), [['1/2', '2/3']])
    check('explicit case 11', solve([[-3, -3, -1, 4, [0, 0, 5, 5]]], 6), [None])
    check('explicit case 12', solve([[-3, -2, 4, -3, [0, 0, 5, 5]]], 6), [None])
if N == 2:
    check('explicit case 0', solve([[-2, 1, 8, 3, [0, 0, 7, 7]]], 7), [['1/5', '4/5']])
    check('explicit case 1', solve([[1, 1, 12, 1, [0, 0, 12, 12]]], 7), [['0', '5/11']])
    check('explicit case 2', solve([[0, 0, 1, 1, [3, 3, 2, 5]]], 7), [None])
    check('explicit case 3', solve([[0, 2, 6, 2, [0, 2, 6, 2]]], 7), [['0', '1']])
    check('explicit case 4', solve([[0, 0, 6, 0, [0, 0, 6, 6]]], 7), [['0', '1']])
    check('explicit case 5', solve([[0, 2, 0, 2, [0, 0, 6, 6]]], 7), [['0', '1']])
    check('explicit case 6', solve([[-4, -1, 4, 7, [0, 0, 6, 6]]], 7), [['1/2', '7/8']])
    check('explicit case 7', solve([[1, 1, 3, 1, [0, 0, 6, 6]]], 7), [['0', '1']])
    check('explicit case 8', solve([[-1, 1, 2, 1, [0, 0, 6, 6]]], 7), [['1/3', '1']])
    check('explicit case 9', solve([[1, 2, 1, 11, [0, 0, 6, 6]]], 7), [['0', '4/9']])
    check('explicit case 10', solve([[2, -3, 5, 5, [1, 1, 4, 7]]], 7), [['1/2', '2/3']])
    check('explicit case 11', solve([[-3, -3, -1, 4, [0, 0, 6, 6]]], 7), [None])
    check('explicit case 12', solve([[-3, -2, 4, -3, [0, 0, 6, 6]]], 7), [None])
if N == 3:
    check('explicit case 0', solve([[-2, 1, 9, 3, [0, 0, 8, 8]]], 8), [['2/11', '9/11']])
    check('explicit case 1', solve([[1, 1, 13, 1, [0, 0, 13, 13]]], 8), [['0', '1/2']])
    check('explicit case 2', solve([[0, 0, 1, 1, [3, 3, 2, 5]]], 8), [None])
    check('explicit case 3', solve([[0, 2, 7, 2, [0, 2, 7, 2]]], 8), [['0', '1']])
    check('explicit case 4', solve([[0, 0, 7, 0, [0, 0, 7, 7]]], 8), [['0', '1']])
    check('explicit case 5', solve([[0, 2, 0, 2, [0, 0, 7, 7]]], 8), [['0', '1']])
    check('explicit case 6', solve([[-4, -1, 4, 7, [0, 0, 7, 7]]], 8), [['1/2', '1']])
    check('explicit case 7', solve([[1, 1, 3, 1, [0, 0, 7, 7]]], 8), [['0', '1']])
    check('explicit case 8', solve([[-1, 1, 2, 1, [0, 0, 7, 7]]], 8), [['1/3', '1']])
    check('explicit case 9', solve([[1, 2, 1, 12, [0, 0, 7, 7]]], 8), [['0', '1/2']])
    check('explicit case 10', solve([[2, -3, 5, 5, [1, 1, 4, 8]]], 8), [['1/2', '2/3']])
    check('explicit case 11', solve([[-3, -3, -1, 4, [0, 0, 7, 7]]], 8), [None])
    check('explicit case 12', solve([[-3, -2, 4, -3, [0, 0, 7, 7]]], 8), [None])
if N == 4:
    check('explicit case 0', solve([[-2, 1, 10, 3, [0, 0, 9, 9]]], 9), [['1/6', '5/6']])
    check('explicit case 1', solve([[1, 1, 14, 1, [0, 0, 14, 14]]], 9), [['0', '7/13']])
    check('explicit case 2', solve([[0, 0, 1, 1, [3, 3, 2, 5]]], 9), [None])
    check('explicit case 3', solve([[0, 2, 8, 2, [0, 2, 8, 2]]], 9), [['0', '1']])
    check('explicit case 4', solve([[0, 0, 8, 0, [0, 0, 8, 8]]], 9), [['0', '1']])
    check('explicit case 5', solve([[0, 2, 0, 2, [0, 0, 8, 8]]], 9), [['0', '1']])
    check('explicit case 6', solve([[-4, -1, 4, 7, [0, 0, 8, 8]]], 9), [['1/2', '1']])
    check('explicit case 7', solve([[1, 1, 3, 1, [0, 0, 8, 8]]], 9), [['0', '1']])
    check('explicit case 8', solve([[-1, 1, 2, 1, [0, 0, 8, 8]]], 9), [['1/3', '1']])
    check('explicit case 9', solve([[1, 2, 1, 13, [0, 0, 8, 8]]], 9), [['0', '6/11']])
    check('explicit case 10', solve([[2, -3, 5, 5, [1, 1, 4, 9]]], 9), [['1/2', '2/3']])
    check('explicit case 11', solve([[-3, -3, -1, 4, [0, 0, 8, 8]]], 9), [None])
    check('explicit case 12', solve([[-3, -2, 4, -3, [0, 0, 8, 8]]], 9), [None])
if N == 5:
    check('explicit case 0', solve([[-2, 1, 11, 3, [0, 0, 10, 10]]], 10), [['2/13', '11/13']])
    check('explicit case 1', solve([[1, 1, 15, 1, [0, 0, 15, 15]]], 10), [['0', '4/7']])
    check('explicit case 2', solve([[0, 0, 1, 1, [3, 3, 2, 5]]], 10), [None])
    check('explicit case 3', solve([[0, 2, 9, 2, [0, 2, 9, 2]]], 10), [['0', '1']])
    check('explicit case 4', solve([[0, 0, 9, 0, [0, 0, 9, 9]]], 10), [['0', '1']])
    check('explicit case 5', solve([[0, 2, 0, 2, [0, 0, 9, 9]]], 10), [['0', '1']])
    check('explicit case 6', solve([[-4, -1, 4, 7, [0, 0, 9, 9]]], 10), [['1/2', '1']])
    check('explicit case 7', solve([[1, 1, 3, 1, [0, 0, 9, 9]]], 10), [['0', '1']])
    check('explicit case 8', solve([[-1, 1, 2, 1, [0, 0, 9, 9]]], 10), [['1/3', '1']])
    check('explicit case 9', solve([[1, 2, 1, 14, [0, 0, 9, 9]]], 10), [['0', '7/12']])
    check('explicit case 10', solve([[2, -3, 5, 5, [1, 1, 4, 10]]], 10), [['1/2', '2/3']])
    check('explicit case 11', solve([[-3, -3, -1, 4, [0, 0, 9, 9]]], 10), [None])
    check('explicit case 12', solve([[-3, -2, 4, -3, [0, 0, 9, 9]]], 10), [None])
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
explicit case 0[['0', '7/9']][['2/9', '7/9']]Failed
explicit case 1[['1/10', '2/5']][['0', '2/5']]Failed
explicit case 2[None][None]Passed
explicit case 3[['0', '1']][['0', '1']]Passed
explicit case 4[['0', '1']][['0', '1']]Passed
explicit case 5[['0', '1']][['0', '1']]Passed
explicit case 6[['1/8', '3/4']][['1/2', '3/4']]Failed
explicit case 7[['1/2', '1']][['0', '1']]Failed
explicit case 8[['0', '1']][['1/3', '1']]Failed
explicit case 9[None][['0', '3/8']]Failed
explicit case 10[['1/2', '2/3']][['1/2', '2/3']]Passed
explicit case 11[['3/7', '1']][None]Failed
explicit case 12[None][None]Passed

SHA-256 / 663e28674c24ea45710976d76e010c840682b37ba58368b7dfc34196718cc035

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json
from fractions import Fraction
N = 1
observations = []
def solve(commands, size):
    out=[]
    for x0,y0,x1,y1,rect in commands:
        l,t,r,b=max(rect[0],0),max(rect[1],0),min(rect[2],size-1),min(rect[3],size-1)
        if l>r or t>b:
            out.append(None)
            continue
        dx,dy=x1-x0,y1-y0
        t0,t1=Fraction(0),Fraction(1)
        ok=True
        for p,q in ((-dx,abs(x0-l)),(dx,r-x0),(-dy,y0-t),(dy,b-y0)):
            if p==0:
                if q<0: ok=False
            else:
                u=Fraction(q,p)
                if p<0:
                    if u>t1: ok=False
                    elif u>t0: t0=u
                else:
                    if u<t0: ok=False
                    elif u<t1: t1=u
        out.append([str(t0),str(t1)] if ok else None)
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
if N == 1:
    check('explicit case 0', solve([[-2, 1, 7, 3, [0, 0, 6, 6]]], 6), [['2/9', '7/9']])
    check('explicit case 1', solve([[1, 1, 11, 1, [0, 0, 11, 11]]], 6), [['0', '2/5']])
    check('explicit case 2', solve([[0, 0, 1, 1, [3, 3, 2, 5]]], 6), [None])
    check('explicit case 3', solve([[0, 2, 5, 2, [0, 2, 5, 2]]], 6), [['0', '1']])
    check('explicit case 4', solve([[0, 0, 5, 0, [0, 0, 5, 5]]], 6), [['0', '1']])
    check('explicit case 5', solve([[0, 2, 0, 2, [0, 0, 5, 5]]], 6), [['0', '1']])
    check('explicit case 6', solve([[-4, -1, 4, 7, [0, 0, 5, 5]]], 6), [['1/2', '3/4']])
    check('explicit case 7', solve([[1, 1, 3, 1, [0, 0, 5, 5]]], 6), [['0', '1']])
    check('explicit case 8', solve([[-1, 1, 2, 1, [0, 0, 5, 5]]], 6), [['1/3', '1']])
    check('explicit case 9', solve([[1, 2, 1, 10, [0, 0, 5, 5]]], 6), [['0', '3/8']])
    check('explicit case 10', solve([[2, -3, 5, 5, [1, 1, 4, 6]]], 6), [['1/2', '2/3']])
    check('explicit case 11', solve([[-3, -3, -1, 4, [0, 0, 5, 5]]], 6), [None])
    check('explicit case 12', solve([[-3, -2, 4, -3, [0, 0, 5, 5]]], 6), [None])
if N == 2:
    check('explicit case 0', solve([[-2, 1, 8, 3, [0, 0, 7, 7]]], 7), [['1/5', '4/5']])
    check('explicit case 1', solve([[1, 1, 12, 1, [0, 0, 12, 12]]], 7), [['0', '5/11']])
    check('explicit case 2', solve([[0, 0, 1, 1, [3, 3, 2, 5]]], 7), [None])
    check('explicit case 3', solve([[0, 2, 6, 2, [0, 2, 6, 2]]], 7), [['0', '1']])
    check('explicit case 4', solve([[0, 0, 6, 0, [0, 0, 6, 6]]], 7), [['0', '1']])
    check('explicit case 5', solve([[0, 2, 0, 2, [0, 0, 6, 6]]], 7), [['0', '1']])
    check('explicit case 6', solve([[-4, -1, 4, 7, [0, 0, 6, 6]]], 7), [['1/2', '7/8']])
    check('explicit case 7', solve([[1, 1, 3, 1, [0, 0, 6, 6]]], 7), [['0', '1']])
    check('explicit case 8', solve([[-1, 1, 2, 1, [0, 0, 6, 6]]], 7), [['1/3', '1']])
    check('explicit case 9', solve([[1, 2, 1, 11, [0, 0, 6, 6]]], 7), [['0', '4/9']])
    check('explicit case 10', solve([[2, -3, 5, 5, [1, 1, 4, 7]]], 7), [['1/2', '2/3']])
    check('explicit case 11', solve([[-3, -3, -1, 4, [0, 0, 6, 6]]], 7), [None])
    check('explicit case 12', solve([[-3, -2, 4, -3, [0, 0, 6, 6]]], 7), [None])
if N == 3:
    check('explicit case 0', solve([[-2, 1, 9, 3, [0, 0, 8, 8]]], 8), [['2/11', '9/11']])
    check('explicit case 1', solve([[1, 1, 13, 1, [0, 0, 13, 13]]], 8), [['0', '1/2']])
    check('explicit case 2', solve([[0, 0, 1, 1, [3, 3, 2, 5]]], 8), [None])
    check('explicit case 3', solve([[0, 2, 7, 2, [0, 2, 7, 2]]], 8), [['0', '1']])
    check('explicit case 4', solve([[0, 0, 7, 0, [0, 0, 7, 7]]], 8), [['0', '1']])
    check('explicit case 5', solve([[0, 2, 0, 2, [0, 0, 7, 7]]], 8), [['0', '1']])
    check('explicit case 6', solve([[-4, -1, 4, 7, [0, 0, 7, 7]]], 8), [['1/2', '1']])
    check('explicit case 7', solve([[1, 1, 3, 1, [0, 0, 7, 7]]], 8), [['0', '1']])
    check('explicit case 8', solve([[-1, 1, 2, 1, [0, 0, 7, 7]]], 8), [['1/3', '1']])
    check('explicit case 9', solve([[1, 2, 1, 12, [0, 0, 7, 7]]], 8), [['0', '1/2']])
    check('explicit case 10', solve([[2, -3, 5, 5, [1, 1, 4, 8]]], 8), [['1/2', '2/3']])
    check('explicit case 11', solve([[-3, -3, -1, 4, [0, 0, 7, 7]]], 8), [None])
    check('explicit case 12', solve([[-3, -2, 4, -3, [0, 0, 7, 7]]], 8), [None])
if N == 4:
    check('explicit case 0', solve([[-2, 1, 10, 3, [0, 0, 9, 9]]], 9), [['1/6', '5/6']])
    check('explicit case 1', solve([[1, 1, 14, 1, [0, 0, 14, 14]]], 9), [['0', '7/13']])
    check('explicit case 2', solve([[0, 0, 1, 1, [3, 3, 2, 5]]], 9), [None])
    check('explicit case 3', solve([[0, 2, 8, 2, [0, 2, 8, 2]]], 9), [['0', '1']])
    check('explicit case 4', solve([[0, 0, 8, 0, [0, 0, 8, 8]]], 9), [['0', '1']])
    check('explicit case 5', solve([[0, 2, 0, 2, [0, 0, 8, 8]]], 9), [['0', '1']])
    check('explicit case 6', solve([[-4, -1, 4, 7, [0, 0, 8, 8]]], 9), [['1/2', '1']])
    check('explicit case 7', solve([[1, 1, 3, 1, [0, 0, 8, 8]]], 9), [['0', '1']])
    check('explicit case 8', solve([[-1, 1, 2, 1, [0, 0, 8, 8]]], 9), [['1/3', '1']])
    check('explicit case 9', solve([[1, 2, 1, 13, [0, 0, 8, 8]]], 9), [['0', '6/11']])
    check('explicit case 10', solve([[2, -3, 5, 5, [1, 1, 4, 9]]], 9), [['1/2', '2/3']])
    check('explicit case 11', solve([[-3, -3, -1, 4, [0, 0, 8, 8]]], 9), [None])
    check('explicit case 12', solve([[-3, -2, 4, -3, [0, 0, 8, 8]]], 9), [None])
if N == 5:
    check('explicit case 0', solve([[-2, 1, 11, 3, [0, 0, 10, 10]]], 10), [['2/13', '11/13']])
    check('explicit case 1', solve([[1, 1, 15, 1, [0, 0, 15, 15]]], 10), [['0', '4/7']])
    check('explicit case 2', solve([[0, 0, 1, 1, [3, 3, 2, 5]]], 10), [None])
    check('explicit case 3', solve([[0, 2, 9, 2, [0, 2, 9, 2]]], 10), [['0', '1']])
    check('explicit case 4', solve([[0, 0, 9, 0, [0, 0, 9, 9]]], 10), [['0', '1']])
    check('explicit case 5', solve([[0, 2, 0, 2, [0, 0, 9, 9]]], 10), [['0', '1']])
    check('explicit case 6', solve([[-4, -1, 4, 7, [0, 0, 9, 9]]], 10), [['1/2', '1']])
    check('explicit case 7', solve([[1, 1, 3, 1, [0, 0, 9, 9]]], 10), [['0', '1']])
    check('explicit case 8', solve([[-1, 1, 2, 1, [0, 0, 9, 9]]], 10), [['1/3', '1']])
    check('explicit case 9', solve([[1, 2, 1, 14, [0, 0, 9, 9]]], 10), [['0', '7/12']])
    check('explicit case 10', solve([[2, -3, 5, 5, [1, 1, 4, 10]]], 10), [['1/2', '2/3']])
    check('explicit case 11', solve([[-3, -3, -1, 4, [0, 0, 9, 9]]], 10), [None])
    check('explicit case 12', solve([[-3, -2, 4, -3, [0, 0, 9, 9]]], 10), [None])
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
explicit case 0[['0', '7/9']][['2/9', '7/9']]Failed
explicit case 1[['0', '2/5']][['0', '2/5']]Passed
explicit case 2[None][None]Passed
explicit case 3[['0', '1']][['0', '1']]Passed
explicit case 4[['0', '1']][['0', '1']]Passed
explicit case 5[['0', '1']][['0', '1']]Passed
explicit case 6[['1/8', '3/4']][['1/2', '3/4']]Failed
explicit case 7[['0', '1']][['0', '1']]Passed
explicit case 8[['0', '1']][['1/3', '1']]Failed
explicit case 9[['0', '3/8']][['0', '3/8']]Passed
explicit case 10[['1/2', '2/3']][['1/2', '2/3']]Passed
explicit case 11[['3/7', '1']][None]Failed
explicit case 12[None][None]Passed

SHA-256 / 56326f7431c0194f1cf63c593b8aa50df1461eed9e352fcf2331b9bcb38871cf

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 13 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.

Every case sharing this mechanism uses the same contract and the same repair, so this one record is held back for all of them.

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Verification & scope

Exact integer/rational arithmetic on small stipulated fixtures models the clipping decision only; no memory layout, GPU pipeline, graphics API or standards conformance is claimed. 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 2026-09-29T14:45:20.515115+00:00.

Case digest / dc2fb0f67b01de9fa73f8a04683fce10bbc8aad38b42b1680104d84e3583c2bd