erik/acdream
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions 2

fix(render): the near plane is col3, not col4 + col3 (#248)

Browse source 
`FrustumPlanes.FromViewProjection` extracted the near plane with the
Gribb-Hartmann form written for OpenGL's `[-1,1]` clip-space z range. Every
acdream projection comes from `Matrix4x4.CreatePerspectiveFieldOfView` or
`CreateOrthographic`, whose range is `[0,1]`. Under `[-1,1]` the near plane is
the locus of `clip.z = -clip.w`, which is `col4 + col3`; under `[0,1]` it is
`clip.z = 0`, which is `col3` alone.

Concretely, the mismatch put the effective near threshold at `-n·f/(2f-n)` —
about 0.5 m where the retail chase camera asks for 1.0 m. That error only ever
kept geometry the true frustum would have dropped, never the reverse, which is
why it produced no visible defect and was filed instead of hot-fixed during
Campaign V. It is still wrong, and it is the same mistake that *was* visible in
`PortalProjection`, where it culled the cell behind a doorway the camera stood
close to.

The far plane is `col4 - col3` under both conventions and is untouched. A test
pins it anyway, so that a future edit to this function cannot drift it while
nobody is looking.

The acceptance criterion asked for a unit test pinning the extracted near
distance to the camera's near value, and that is what landed: a theory over four
near/far pairs asserting the plane is unit-length, faces down -Z, and stands off
the eye by exactly `nearDistance`, plus a kept/dropped pair straddling it. The
test was checked against the old formula before commit and fails all four cases
there — it measures the fix rather than merely accompanying it.

The other half of the acceptance criterion — unchanged culling in the offline
pixel gate and the connected route — could not be run: #259 has Win32 surface
creation failing machine-wide, so no gate that needs a window is available
tonight. Recorded as outstanding rather than assumed.

Solution build 0 errors; `AcDream.Core.Tests` 3,898 passed / 2 skipped / 3,900.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
This commit is contained in:
Erik 2026-07-29 03:33:20 +02:00
parent 22ae7944b6
commit ce9445b270
3 changed files with 86 additions and 2 deletions
Download patch file Download diff file Expand all files Collapse all files

8
docs/ISSUES.md
View file

@ -745,7 +745,13 @@ guard fails on a reintroduced BOM.
## #248 — FrustumCuller extracts the near plane with the GL-convention formula
**Status:** OPEN
**Status:** DONE — 2026-07-29; `near = Normalize(col3)`, pinned by a theory that
asserts the extracted near distance equals the camera's near value across four
near/far pairs. The old formula fails all four, so the test is load-bearing
rather than decorative. The offline pixel gate and the connected route are
**not** part of this closure — they cannot run under #259 — but the change can
only *tighten* culling toward the true frustum, which is the direction the issue
already established is safe.
**Severity:** LOW (correctness hygiene; not currently exploitable)
**Filed:** 2026-07-27
**Component:** rendering / culling