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docs: A8.F plan — record Task 3 near-clip correction + Task 4 winding requirement

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Erik 2026-05-29 11:59:04 +02:00
parent 9ec83307fc
commit c665f3eef3
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docs/superpowers/plans/2026-05-29-phase-a8f-portal-frame-visibility.md
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@ -410,6 +410,19 @@ git commit -m "feat(render): Phase A8.F — ScreenPolygonClip 2D convex-polygon
## Task 3: `PortalProjection` — project portal polygon to NDC with near-clip
> **Correction (2026-05-29, during execution):** the `w >= WEps` clip in the Step-3 code
> below was a bug — it leaves a clipped vertex at the eye singularity (w≈1e-4) so `x/w` blows
> up (~±7852), relocating the inversion instead of preventing it. The shipped code clips
> against the in-front-of-camera half-space `w + z >= 0` (commit `a28a176`; comments corrected
> in `9ec8330`). That predicate is convention-agnostic: acdream's cameras use
> `Matrix4x4.CreatePerspectiveFieldOfView` (NDC z ∈ **[0,1]**, not GL [-1,1]); the eye (w=0)
> is always excluded so the divide is safe — and **Task 6 needs no projection-convention fix**
> (verified: no `glClipControl`/`glDepthRange` remap anywhere in the codebase). The straddle
> test bound was relaxed `[-10,10]`→`[-50,50]` and a 4th downstream-intersection test added.
> **Task 4 requirement:** `ProjectToNdc` preserves input winding (NOT normalized CCW) — the
> builder MUST apply the portal-side test and feed camera-facing (CCW) portals to the CCW-only
> `ScreenPolygonClip`, and Task 4's conformance tests should assert a winding/back-face case.
Transform a cell-local portal polygon to clip space, clip against the in-front-of-camera plane (`w >= eps`) to prevent inversion when a portal straddles the camera, then perspective-divide to NDC. Ports the projection in retail `PView::GetClip` (decomp:432344); the `w` clip is the homogeneous form of retail's near-plane sidedness math (`PView::ConstructView(CBldPortal)` decomp:433832-433845).
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