FA-51814 / Raster clipping / Member archive

Polyline strip window clip: closing edge triangle · case 04

Closed triangles never receive their closing edge.

Member previewVariant 4 · 3 implementations · 11 checks per implementation

Case contract

Each command is [points,closed]. Consecutive vertices (plus the closing edge when closed and at least three points) are clipped against the closed pixel-center window [0,size-1]x[0,size-1] with exact parametric clipping. Visible parts that start where the current piece ends extend it (skipping zero-length repeats); any other visible part starts a new piece; a fully rejected edge ends the current piece. For closed paths, a last piece ending where the first piece begins is merged in front of it without repeating the joint. Pieces with fewer than two vertices are dropped. Vertices are exact rational strings.

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 6	`[[[["1", "1"], ["3", "1"], ["2", "3"]]]]`	`[[[["1", "1"], ["3", "1"], ["2", "3"], ["1", "1"]]]]`	Failed

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This record includes three runnable implementations, regression fixtures, execution results, and source hashes.

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