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knife-edge port: polyClipFinish W=0 eye-plane clip + degenerate-view propagation; EyeInsidePortalOpening rescue DELETED

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Ports retail ACRender::polyClipFinish (0x006b6d00, pc:702749) near-eye
semantics into PortalProjection.ProjectToClip - the fundamental fix for
the in-plane portal clip family (climb strobes, tower-top roof/floor
flap while turning; live-corroborated this session: [viewer-diff]
0xAAB30108 strobing 27x mid-climb, whole interior dropping at the top).
Pseudocode: docs/research/2026-06-11-polyclipfinish-w0-clip-pseudocode.md.

Three legs, all decomp-driven:

1. ProjectToClip clips at w >= 0 EXACTLY (was EyePlaneW=1e-4), with
   retail's any-negative-w gate. Boundary intersections land at w == 0
   (homogeneous directions), so a portal the eye is CROSSING yields the
   correct unbounded half-region that the bounded view-region clip cuts
   to the screen. A w=0 vertex cannot survive a bounded region clip
   into the divide (direction fails some edge of any bounded convex
   region); the measure-zero corner case is guarded non-finite->empty.

2. CellView.CanonicalKey keys ALL-COLLINEAR (zero-area) views as their
   snapped segment ("L:" + extremes) instead of rejecting them - retail
   PROPAGATES degenerate views (ClipPortals decomp:433651-433711
   forwards any count!=0 GetClip output, no area gate anywhere), keeping
   the cell behind an exactly-in-plane portal in the draw list (cells
   draw whole; onward floods die naturally). Rejection dropped the
   whole chain for the frame - the parked-eye knife-edge band. Finite
   key space unchanged -> dedup + strict-growth convergence intact.

3. The EyeInsidePortalOpening rescue is DELETED (the T2-documented
   compensation for the 1e-4 divergence) along with EyeStandingPerpDist
   + PointInPoly2D. Empty clip = no flood, period (retail's rule).
   CornerFloodReplay - the gate that REFUTED the previous deletion
   attempt - passes WITHOUT the rescue under the W=0 port.

Harness criterion corrected to retail's rules (it codified the rescue):
cells fully BEHIND the camera are not required (all-behind portals clip
empty in retail); monotone area holds per root regime; the two
manufactured exact-on-plane steps assert root-only (boundary root pick
is ambiguous; the in-plane portal there is ~perpendicular to the gaze =
genuinely off-screen). Build_CollapsedInteriorPortalNearEye test
inverted to pin the retail empty-clip rule (it pinned the rescue).

New pins: eye-crossing portal -> w==0 boundary verts + half-region (not
sliver); gaze-along-plane degenerate view accepted + segment-key dedup;
non-finite guard. Replay harnesses (CornerFloodReplay, Issue120,
TowerAscent, HouseExit, Issue127) all green.

Suites: App 246+1skip / Core 1430+2skip / UI 420 / Net 294.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
This commit is contained in:
Erik 2026-06-11 21:44:23 +02:00
parent 2163308032
commit 987313aa54
7 changed files with 357 additions and 130 deletions
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38
src/AcDream.App/Rendering/PortalView.cs
View file

@ -167,10 +167,20 @@ public sealed class CellView
// Canonical key for a view polygon: vertices snapped to the NDC grid, consecutive snap-duplicates
// removed (including wrap-around), COLLINEAR points removed (exact integer cross-products on the
// snapped grid), then rotated to start at the lexicographically smallest vertex so a rotated
// emission of the same cycle yields the same key. Returns null when fewer than 3 distinct
// snapped vertices survive (a degenerate sliver, not a real region). Winding is already CCW for every
// emission of the same cycle yields the same key. Winding is already CCW for every
// builder input (ClipToRegion / EnsureCcw), so the cyclic order is canonical without a reversal step.
//
// W=0 port (2026-06-11): an ALL-COLLINEAR polygon (zero area) keys as its snapped segment
// ("L:" + extreme points) instead of null. A portal whose plane contains the eye projects to
// exactly this — and retail PROPAGATES it: PView::ClipPortals (decomp:433651-433711) forwards
// any GetClip output with count != 0 to copy_view/OtherPortalClip with no area gate anywhere,
// so the neighbour cell stays in the draw list (cells draw whole; onward floods die naturally
// against the zero-area region). Rejecting these views dropped the whole chain behind an
// exactly-in-plane portal for the frame — the parked-eye knife-edge band (tower deck, spiral
// landings). The segment key space is finite like the area-key space, so dedup + the strict
// growth convergence invariant are unchanged. Returns null only when fewer than 2 distinct
// snapped points survive (a true sub-grid point — not a real region OR segment).
//
// §4 corner/doorway fix (2026-06-10) — the collinear pass: the homogeneous region clipper
// (PortalProjection.ClipToRegion, used by the forward AND — as of today — the reciprocal hop)
// legitimately inserts intersection vertices ON a subject edge when a region edge grazes it, so
@ -192,10 +202,15 @@ public sealed class CellView
}
if (pts.Count >= 2 && pts[^1] == pts[0]) pts.RemoveAt(pts.Count - 1);
// Snapshot the distinct snapped points BEFORE collinear removal — the all-collinear
// fallback keys off the segment EXTREMES of the full point set (stable across
// re-emissions regardless of the removal loop's order).
List<(int X, int Y)>? preCollinear = pts.Count >= 2 ? new List<(int, int)>(pts) : null;
// Remove collinear points: for consecutive (prev, cur, next) around the cycle, drop cur when
// cross(cur-prev, next-cur) == 0 — exact in integer grid coordinates (deltas ≤ ~4000, products
// ≤ ~1.6e7, no overflow). Loop to a fixpoint: removing one point can make its neighbour
// collinear. Degenerate inputs (all points on one line) reduce below 3 → rejected below.
// collinear. All-collinear inputs reduce below 3 → the segment-key fallback below.
bool removed = true;
while (removed && pts.Count >= 3)
{
@ -215,7 +230,22 @@ public sealed class CellView
}
}
}
if (pts.Count < 3) return null;
if (pts.Count < 3)
{
// Zero-area (all-collinear) view — key as its snapped segment so retail's
// degenerate-view propagation works (see method doc). Extremes are the
// lexicographic min/max of the full snapped point set.
if (preCollinear is null) return null;
var lo = preCollinear[0];
var hi = preCollinear[0];
foreach (var q in preCollinear)
{
if (q.X < lo.X || (q.X == lo.X && q.Y < lo.Y)) lo = q;
if (q.X > hi.X || (q.X == hi.X && q.Y > hi.Y)) hi = q;
}
if (lo == hi) return null; // a sub-grid point — not a region or a segment
return $"L:{lo.X},{lo.Y};{hi.X},{hi.Y};";
}
int n = pts.Count;
int best = 0;