FA-51534 / Raster clipping / Member archive
Cohen sutherland pixel window: right edge inclusive · case 04
A pixel center exactly on the last column is classified as outside, so clipping it back onto the same edge never clears the outcode and the segment is dropped.
Case contract
Each command is a segment [x0,y0,x1,y1] whose endpoints are integers or exact decimal/rational strings in pixel-center coordinates. The window is the closed square [0,size-1]x[0,size-1] of pixel centers. Outcodes use strict outside tests (left 1, right 2, below 4, above 8). Both codes zero accepts; a shared bit rejects; otherwise the outside endpoint (endpoint 0 first) is moved to the highest set edge in above, below, right, left order and its code is recomputed from the new point; a clip against an edge parallel to the segment is treated as a rejection. At most five iterations are allowed; an unresolved or rejected segment returns None. Accepted endpoints round half-up to integer pixels.
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 fixtureThis sample comes from the broken implementation of a controlled reproducer.
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| explicit case 1 | [null] | [[0, 2, 8, 2]] | Failed |
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