FA-51582 / Raster clipping / Member archive

Liang barsky parametric rect: parallel boundary exclusive · case 02

A segment parallel to and lying exactly on a clip boundary is rejected although boundary points are inside.

Member previewVariant 2 · 3 implementations · 13 checks per implementation

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.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
explicit case 3	`[null]`	`[["0", "1"]]`	Failed

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