Three fixes to match retail CLandBlock::get_land_scenes (0x00530460):
1. Loop bound: iterate 9×9 vertices (side_vertex_count=9), not 8×8
cells. Edge vertices (x=8 or y=8) produce valid spawns when the
per-object displacement shifts the position back into [0, 192).
Confirmed by named retail decomp do-while condition, WorldBuilder
vertLength=9, ACViewer Terrain.Count=81, AC2D wTopo[9][9].
2. Building suppression: check at the DISPLACED position's cell
(CSortCell::has_building per spawn), not at the loop vertex index.
Matches WorldBuilder buildingsGrid[gx2, gy2] pattern.
3. Slope filter: replace finite-difference gradient approximation
with triangle-aware normal sampling via new static method
TerrainSurface.SampleNormalZFromHeightmap. Picks the correct
triangle via IsSplitSWtoNE, matching retail find_terrain_poly →
polygon->plane.N.z and WorldBuilder's GetNormal().
Tests: 5 new tests for SampleNormalZFromHeightmap (flat=1.0, sloped<1,
cross-validates with SampleSurface instance method) and DisplaceObject
edge-vertex validity.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Closes#48. Trees on sloped cells visibly hovered above the visible
terrain because GameWindow.SampleTerrainZ (the bilinear fallback used
during scenery hydration before physics registers a landblock) had
its diagonal arms swapped — used the SEtoNW triangle test on SWtoNE
cells and vice versa. The ACDREAM_DUMP_SCENERY_Z=1 diagnostic showed
every scenery line ran through the bilinear path (streaming race),
so on hilly terrain scenery was placed at a Z up to ~1.5 m off from
the visible mesh.
Latent since ff325ab (2026-04-17 "feat(ui): debug overlay + refined
input controls" carrying along the upgrade). That commit reached for
WorldBuilder TerrainUtils.GetHeight as the secondary oracle and
re-derived the triangle-pair tests; the named-retail / ACE algorithm
in TerrainSurface.SampleZ (used by the physics path / player Z) was
always correct, so player feet stayed flush — the two paths just
disagreed and only scenery noticed.
Fix:
- TerrainSurface.InterpolateZInTriangle (private static) — single
source of truth for the triangle pick + barycentric Z, sourced
from FUN_00532a50 / ACE LandblockStruct.ConstructPolygons.
- TerrainSurface.SampleZFromHeightmap (public static) — heightmap-
byte-array variant for the scenery hydration fallback. Both this
and TerrainSurface.SampleZ (instance) now delegate to the same
InterpolateZInTriangle.
- GameWindow.SampleTerrainZ — thin wrapper over the new static.
- TerrainSurfaceTests.SampleZFromHeightmap_AgreesWithInstance_AcrossWholeLandblock
asserts both sampler paths agree at 1500 sample points across both
diagonals, so future drift gets caught.
The ACDREAM_DUMP_SCENERY_Z=1 diagnostic in BuildSceneryEntitiesForStreaming
is kept committed (env-var gated, zero cost when off) — useful for
the related #49 scenery (X, Y) placement investigation filed in the
same commit.
Visual verified at Holtburg landblock 0xA9B30001 2026-05-06: the
formerly floating 32 m pines (setups 0x020002D3 / 0x020002D9) now
sit flush on the visible terrain mesh.
Test baseline: dotnet test reports the same 8 pre-existing motion /
BSP step-up failures as the handoff doc warned about — no new
failures introduced.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Port the first retail precipice-slide slice from named retail/ACE: terrain and BSP walkable hits now preserve polygon vertices, failed step-down edges back-probe to rediscover the walkable polygon, and edge-slide can run precipice/cliff slide instead of only hard-stopping.
Adds pseudocode anchors plus regression coverage for terrain polygon context and loaded-terrain boundary edge-slide.
Co-authored-by: Codex <codex@openai.com>
Two coupled physics fixes that together resolve "+Acdream walks on top of
water instead of submerged" and "brief Falling animation when running up
steep hills".
## 1. Water depth = physics adjustment, not rendering
Retail has NO separate water surface mesh. Characters visually submerge
in water because ValidateWalkable adds `waterDepth` to its signed-distance
check (ACE ObjectInfo.cs:124), letting the character's feet sit below the
terrain plane by that amount before the push-up fires. Rendered character
below rendered terrain = looks submerged.
Our ValidateWalkable didn't carry a waterDepth, so feet were always
snapped exactly to the plane. Water cells looked like walking on water.
Added:
- TerrainSurface now carries per-vertex water flags (bits 2-6 of
TerrainInfo → SurfChar lookup) and per-cell classification.
- TerrainSurface.SampleWaterDepth(localX, localY) returns 0.0 (dry),
0.45 (partial-water near water corner), 0.9 (entirely water). Deviates
from retail's 0.1 fallback for "dry corner of partial-water cell" —
that 0.1 destabilizes the "feet exactly on plane" contact-touch check
in ValidateWalkable (dist > EPSILON, SetContactPlane skipped,
ValidateTransition clears OnWalkable, gravity applies, character
micro-falls each frame).
- PhysicsEngine.SampleWaterDepth is the world-space wrapper.
- FindEnvCollisions samples the per-point depth and forwards it.
- ValidateWalkable adds +waterDepth to the signed-distance check (this
is the ACE-line-124 port).
GameWindow.ApplyLoadedTerrain extracts the low byte of each TerrainInfo
ushort and passes it to the TerrainSurface ctor so classification works.
## 2. AdjustOffset safety-push threshold on sloped planes
The LocalSphere is positioned at `(0, 0, radius)` — center along world
+Z from the character root. On a tilted plane the sphere center's
perpendicular distance to that plane is `radius * Normal.Z`, NOT
`radius`. The original threshold `dist < radius - EPS` therefore fires
spuriously on every slope and the follow-up push-up lifts feet by
`radius * (sec θ - 1)` — 7 cm at 30°, 20 cm at 45°, 48 cm at 60°.
The steep-slope lift is large enough to break ValidateWalkable's
contact-touch check, ValidateTransition then clears OnWalkable,
calc_acceleration applies gravity, and the character flickers into the
Falling animation for ~0.3s while running uphill. User-observed on steep
hills after today's water-depth work made the artifact visible (before
that, general hover masked it).
Fix: the threshold is `radius * Normal.Z` (the natural resting distance
of a Z-axis sphere on the plane). The push fires only when feet are
actually penetrating below natural resting, not on any sloped plane.
ACE's Transition.cs AdjustOffset has the original threshold but the bug
is invisible server-side.
All 717 tests green. Water submersion + steep-slope running both
user-visually verified.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Our previous FindEnvCollisions built a FLAT contact plane (Normal = +Z)
at the sampled terrain Z, discarding the triangle's actual slope.
Retail uses the real terrain polygon's plane (ACE Landblock.cs:125-137
find_terrain_poly → walkable.Plane) which IS sloped.
Without a true slope normal, AdjustOffset's projection of horizontal
velocity onto the plane produces no slope-aligned Z component — fine
for step-subdivision on flat ground, visibly wrong whenever the contact
plane is carried across frames (via PhysicsBody.ContactPlane persistence
from commit 93cbabb): the projection is a no-op and movement is purely
kinematic. With the real slope normal, projected motion correctly
follows the slope.
Not a user-visible bug fix by itself (DIAG LocalZ shows delta≈0 for the
local player everywhere; the "looks too high in water" issue the user
reported is actually a missing water-rendering feature, not a physics
bug). Landing it anyway because it matches retail behavior and removes
the "flat-plane-is-fine" assumption that would bite on any future
contact-plane-dependent code.
Additions:
- TerrainSurface.SampleSurface(localX, localY) → (Z, Normal), deriving
the plane normal analytically from the triangle's height gradient.
Matches the same triangle SampleZ already interpolates through.
- PhysicsEngine.SampleTerrainPlane(worldX, worldY) → System.Numerics.Plane,
the wrapper that bridges terrain space to transition space.
- TransitionTypes.FindEnvCollisions uses SampleTerrainPlane instead of
synthesizing a flat plane from SampleTerrainZ.
All 717 tests green. Flat-plane case is unchanged (Normal.Z = 1 when
the triangle is level, identical to the old plane).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Our LandblockMesh, terrain.vert corner tables, and TerrainSurface.SampleZ
used the OPPOSITE diagonal for each CellSplitDirection enum value from
what ACE (and the decompiled retail client at FUN_00532a50) picks for the
same sign bit. Same formula, same sign-bit mapping, inverted geometry.
Symptom: remote players rendered at server-broadcast Z hovered or clipped
by up to ~1m on sloped cells. Flat cells masked the bug because all four
corner heights were equal so any triangle pair returned the same Z. Live
diagnostic confirmed +0.79m hover on cell (7,5) at lb(AA,B4) — a ~20°
slope — while flat neighbors agreed to floating-point noise.
Three coordinated edits so CPU mesh + GPU corner lookup + CPU sampler all
agree on the retail geometry:
- LandblockMesh: SWtoNE branch now emits {BL,BR,TR}+{BL,TR,TL} (y=x cut),
SEtoNW emits {BL,BR,TL}+{BR,TR,TL} (x+y=1 cut).
- terrain.vert: corner-index tables updated to match.
- TerrainSurface.SampleZ: swapped the two branches' interpolation.
After the fix, 19 live DIAG samples across flat + two slope transitions
all land within 0.01m of server Z. Staircase pattern during remote motion
on slopes is a separate bug (no per-frame collision resolution) and will
be addressed via the transition/FindValidPosition port.
Cross-verified against: ACE LandblockStruct.ConstructPolygons lines 221-
244, decompiled retail FUN_00532a50 (chunk_00530000.c:2235), ClientReference
IsSWtoNECut (tests/AcDream.Core.Tests/Terrain/ClientReference.cs).
Updated test SplitDirection_TerrainSurface_AgreesWith_TerrainBlending
with corrected expectations (Z values swap between the two branches).
All 717 tests green.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
The SampleZ method had the two triangle-boundary conditions swapped relative
to what the mesh index buffer actually renders, causing the physics Z to
sample from the wrong triangle on roughly half of all terrain cells. The
error could be up to 7.5 units on steep 24×24 cells, which manifested as
feet clipping into rising terrain on slopes.
Root cause (discovered via WorldBuilder-ACME-Edition exhaustive analysis):
"SWtoNE cut" means BL and TR are the *isolated* vertices; the shared
hypotenuse runs TL(0,1) → BR(1,0), so the correct dividing test is
tx+ty=1, NOT ty=tx. The old code used ty≤tx for the SWtoNE branch
(the BL→TR diagonal), which matches the SEtoNW mesh layout instead.
Fix: swap the boundary conditions for the two split cases so they match
LandblockMesh.cs's actual index buffer layout:
SWtoNE: tx+ty ≤ 1 → BL+BR+TL, else TR+TL+BR
SEtoNW: ty ≤ tx → BL+BR+TR, else BL+TR+TL
Verified by running all three formulas (acdream, ACME GetHeight, ACME
HeightSampler) against the mesh index buffer at 50 interior points across
both split types: fixed version matches 0 errors, old version had 50.
All 283 tests still pass.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
The triangle-aware Z sampling from the previous commit produces exact
terrain-surface Z values, but a point-sampled Z on a tilted surface
places the character's center on the surface while their feet (which
extend horizontally) clip into the rising terrain ahead/behind.
Fix: in PlayerMovementController, sample Z 1 unit ahead in the walk
direction and add 40% of the gradient as an upward bias. This
compensates for the character's collision cylinder radius on slopes
while producing zero bias on flat ground. The bias is applied in the
movement controller (gameplay concern) not in TerrainSurface.SampleZ
(which stays exact for physics/tests).
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Two fundamental terrain fixes based on the AC2D + holtburger deep dive:
1. Terrain split formula: replaced WorldBuilder's physics-path formula
(214614067/1813693831) with AC2D's render-path formula (0x0CCAC033,
0x421BE3BD, 0x6C1AC587, 0x519B8F25). The two produce different splits
for some cells. Since the render mesh uses this formula, the physics
Z sampler must match it to avoid misalignment on slopes.
2. Triangle-aware Z: replaced bilinear interpolation in TerrainSurface
with per-triangle barycentric interpolation. Each cell is split into
two triangles (using the same AC2D formula). SampleZ determines which
triangle the query point falls in, then interpolates within that
triangle. This produces Z values that exactly match the visual terrain
mesh — no more slope clipping.
Removes the multi-point Z sampling hack from PlayerMovementController
(no longer needed with exact triangle Z).
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Extracts the bilinear heightmap interpolation from GameWindow's
inlined SampleTerrainZ into a reusable class. Also adds outdoor
cell ID computation (8×8 grid of 24-unit cells, 0x0001..0x0040).
First component of the physics collision engine.
6 new tests, all green.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
