The user's "thin strip of background color along the TOP outer edge of a
doorway, looking out from inside" is the landscape-slice scissor box, not
the W=0 clip port.
Mechanism (pinned headlessly, Issue130DoorwayStripTests, 147 eye/gaze
combos at the real Holtburg A9B4 0x0170 exit door):
- BeginDoorwayScissor converted the slice NDC AABB to pixels as
Floor(origin) + Ceiling(size). The far edge floor(min)+ceil(max-min)
lands up to ONE PIXEL SHORT of the true top/right edge at unlucky
fractional alignments (captured: top edge y=0.7938 @1080p -> row 968
cut; right edge column 1296 @1920 cut).
- The scissor brackets the ENTIRE landscape slice (sky, terrain, outdoor
statics, weather). The exit-portal SEAL stamps the full raw aperture at
true depth and the shell wall ends at the aperture edge, so the cut row
never receives any color write -> clear color, flickering with eye
movement as the fractional alignment shifts.
- This violated AD-17's own invariant (over-inclusion is safe,
UNDER-inclusion is the bug class). No register change: the fix restores
the row's documented doctrine.
Lead 1 (987313a W=0 clip port regression) REFUTED by the same harness:
the CPU polygon pipeline (ProjectToClip -> ClipToRegion merges ->
ClipPlaneSet planes) is sub-pixel exact against the raw aperture
projection (worst 0.54 px, 0.00 px aligned). For an all-in-front doorway
polygon the port is bit-identical to the old 1e-4 path by construction.
The EyeInsidePortalOpening rescue stays deleted.
Fix: conservative outer bound floor(min)/ceil(max) extracted to
NdcScissorRect.ToPixels (GL-free; containment property proven in the
header comment); BeginDoorwayScissor delegates.
Pins:
- NdcScissorRectTests: center-inside containment across 251 fractional
alignments x 2 framebuffer sizes + both captured regression cases.
- Issue130DoorwayStripTests: production flood + assembler at the real
exit door; asserts the scissor never cuts a plane-admitted fragment
(worstScissorGap 0.00 px post-fix, was 10.8 px capped) and the CPU
pipeline stays sub-pixel exact (canary 1.2 px).
Suites: App 252+1skip / Core 1439+2skip / UI 420 / Net 294 green.
Awaiting the user visual gate at a cottage doorway.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
6c4b6d64d9