fix #172: port the retail CCylSphere collision family (platform step-up)
The Holtburg town-network portal platform (stab 0xC0A9B465, Setup 0x020019E3, CylSphere r=2.597m h=0.256m) blocked the player with an endless rim slide instead of retail's step-up-onto-top — gating the whole #137 dungeon repro. Surfaced when #149 started registering BSP-less stab CylSpheres: the collision SHAPE became right while the RESPONSE was still the hand-rolled AP-6 approximation (step-up gate + radial wall-slide only). Root cause: no cylinder-TOP support anywhere. DoStepUp's internal step-down probe needs retail's step_sphere_down (0x0053a9b0) to land on the flat top — a cylinder has no polygons for the walkable search — so every step-up onto a wide cylinder failed into StepUpSlide and the player orbited the rim (probe-confirmed: [cyl-test] result=Slid with horizontal rim normals, launch-137-repro.log). Port the full family verbatim: dispatcher intersects_sphere 0x0053b440 (placement/ethereal detection, step-down cap landing, walkable probe, grounded step_sphere_up 0x0053b310, PathClipped collide_with_point 0x0053acb0, airborne land_on_cylinder 0x0053b3d0, Collide-flag exact-TOI cap rest) + collides_with_sphere 0x0053a880 + normal_of_collision 0x0053ab50 + slide_sphere 0x0053b2a0. Pseudocode + settled BN x87 ambiguities (via ACE cross-ref) + two ACE bugs found and NOT copied (head-slide foot-disp; see doc §8): docs/research/2026-07-05-ccylsphere-collision-family-pseudocode.md Ethereal cylinders now flow through retail's Layer-2 override (pc:276961) instead of the early-OK consume — same net #150 behavior, plus retail placement-blocked-by-cylinder semantics. SlideSphere gains a sphereNum param (retail slides the head sphere by its own displacement, 0x0053b843). Register: AP-6 retired; AP-83 added (PerfectClip TOI tail decoded per ACE, dead code until missiles). Tests: CylSphereFamilyTests (grounded step-up onto the exact platform shape, tall-cylinder block, airborne top landing, ethereal guard); the #42 self-shadow control assertion updated to the retail observable (denied movement — the old ~1m radial self-push was the approximation's artifact, not retail). Suites: Core 2533 / App 713 / UI 425 / Net 385 green. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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# CCylSphere collision family — retail pseudocode (port prep)
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**Date:** 2026-07-05 · **Trigger:** the Holtburg town-network portal platform
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(stab `0xC0A9B465`, Setup `0x020019E3`, CylSphere r=2.597 m h=0.256 m) blocks
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the player with an endless rim slide instead of the retail step-up-onto-top.
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Surfaced the moment #149 (`4cf6eeb`) started registering BSP-less stab
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CylSpheres — the collision SHAPE is right; the RESPONSE family was never
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ported. Feeds #137 (dungeon door feet flow through the same dispatcher).
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**Sources:** named-retail pseudo-C (addresses below) = ground truth;
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`references/ACE/Source/ACE.Server/Physics/CylSphere.cs` = cross-reference
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(settles BN x87 garbles; one ACE bug found, noted in §8).
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## Retail function inventory
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| Function | Address | pseudo-C line |
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|---|---|---|
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| `CCylSphere::intersects_sphere(CTransition*)` — dispatcher | `0x0053b440` | :324558 |
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| `CCylSphere::intersects_sphere(Position*, float scale, CTransition*)` — wrapper | `0x0053b8f0` | :324744 |
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| `CCylSphere::collides_with_sphere` | `0x0053a880` | :323943 |
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| `CCylSphere::normal_of_collision` | `0x0053ab50` | :324102 |
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| `CCylSphere::collide_with_point` | `0x0053acb0` | :324173 |
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| `CCylSphere::slide_sphere` | `0x0053b2a0` | :324502 |
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| `CCylSphere::step_sphere_up` | `0x0053b310` | :324516 |
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| `CCylSphere::land_on_cylinder` | `0x0053b3d0` | :324542 |
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| `CCylSphere::step_sphere_down` | `0x0053a9b0` | :324032 |
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| `COLLISIONINFO::set_contact_plane(plane, is_water)` | `0x00509d80` | :271925 |
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## 1. Wrapper (0x0053b8f0) — globalize the cylinder
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```
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intersects_sphere(cyl, Position* objPos, float scale, CTransition* t):
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SPHEREPATH::cache_localspace_sphere(&t->sphere_path, objPos, 1f)
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world_cyl = { low_pt: objPos.localtoglobal(cyl.low_pt * scale),
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radius: cyl.radius * scale,
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height: cyl.height * scale }
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return world_cyl.intersects_sphere(t) // axis stays world-Z
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```
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**acdream mapping:** `ShadowEntry` already stores the globalized base point
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(`Position` = entity pos + rotated scaled local offset, registration sites in
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`GameWindow.cs`) and pre-scaled Radius/CylHeight — the wrapper's work is done
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at registration. `cache_localspace_sphere` matters only for
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`localspace_pos` (used by step_sphere_up's normal rotation, §6).
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## 2. collides_with_sphere (0x0053a880) — pure overlap test
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```
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collides_with_sphere(cyl, CSphere* sphere, Vector3* disp, float radsum):
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// disp = sphere.center − cyl.low_pt (caller computes)
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if (disp.x² + disp.y² <= radsum²) // XY overlap
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halfH = cyl.height * 0.5
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if (|halfH − disp.z| <= sphere.radius − F_EPSILON + halfH) // Z band
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return 1
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return 0
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```
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`radsum` at every call site = `cyl.radius − F_EPSILON + sphere.radius`
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(ε shaved ONCE, in the dispatcher preamble). The ε is what makes "resting
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exactly on the top" a non-overlap, so landings settle instead of re-colliding.
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## 3. Dispatcher (0x0053b440)
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```
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intersects_sphere(cyl, CTransition* t): // cyl in world frame
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sp = t.sphere_path; oi = t.object_info
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s0 = sp.global_sphere[0]; disp0 = s0.center − low_pt
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if sp.num_sphere > 1: s1 = sp.global_sphere[1]; disp1 = s1.center − low_pt
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radsum = cyl.radius − F_EPSILON + s0.radius
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// ── branch 1: placement / ethereal — detection only ──
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if (sp.insert_type == PLACEMENT_INSERT || sp.obstruction_ethereal):
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if collides(s0, disp0) → COLLIDED
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if num_sphere>1 && collides(s1, disp1) → COLLIDED
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return OK
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// ── branch 2: step-down probe — land on the top ──
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if (sp.step_down): return step_sphere_down(t, s0, disp0, radsum)
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// ── branch 3: walkable probe — cylinder occupancy blocks ──
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if (sp.check_walkable):
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if collides(s0, disp0) → COLLIDED
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if num_sphere>1 && collides(s1, disp1) → COLLIDED
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return OK
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// ── branch 4: normal sweep (collide flag clear) ──
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if (!sp.collide):
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if (oi.state & (CONTACT|ON_WALKABLE)): // grounded
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if collides(s0, disp0) → step_sphere_up(t, s0, disp0, radsum)
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if num_sphere>1 && collides(s1, disp1)
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→ slide_sphere(t, s1, disp1, radsum, sphereNum=1) // §8: retail passes disp1
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elif (oi.state & PATH_CLIPPED):
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if collides(s0, disp0) → collide_with_point(t, s0, disp0, radsum, 0)
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else: // airborne
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if collides(s0, disp0) → land_on_cylinder(t, s0, disp0, radsum)
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if num_sphere>1 && collides(s1, disp1)
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→ collide_with_point(t, s1, disp1, radsum, 1)
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return OK
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// ── branch 5: collide-flag re-test — exact-TOI cap landing ──
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if collides(s0,disp0) || (num_sphere>1 && collides(s1,disp1)):
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movement = sp.global_curr_center[0] − s0.center − block_offset(cur→check)
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if |movement.z| < F_EPSILON → COLLIDED
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timecheck = (height + s0.radius − disp0.z) / movement.z
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offset = movement * timecheck
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if radsum² < |xy(offset + disp0)|² → OK // rewound off the cap
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t2 = (1 − timecheck) * sp.walk_interp
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if t2 >= sp.walk_interp || t2 < −0.1 → COLLIDED
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pt = s0.center + offset; pt.z −= s0.radius
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ci.set_contact_plane(Plane(n=(0,0,1), d=−pt.z), is_water=1) // literal 1, §7
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ci.contact_plane_cell_id = sp.check_pos.objcell_id
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sp.walk_interp = t2
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sp.add_offset_to_check_pos(offset)
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return ADJUSTED
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return OK
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```
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State bits (verified against our `ObjectInfoState`): CONTACT=0x1,
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ON_WALKABLE=0x2, PATH_CLIPPED=0x8, PERFECT_CLIP=0x40.
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## 4. step_sphere_down (0x0053a9b0) — land on the top during a step-down probe
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```
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step_sphere_down(t, s0, disp0, radsum):
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if !collides(s0,disp0) && !(num_sphere>1 && collides(s1,disp1)) → OK
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stepScale = sp.step_down_amt * sp.walk_interp
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if |stepScale| < F_EPSILON → COLLIDED
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deltaz = height + s0.radius − disp0.z // lift so bottom rests on top
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interp = (1 − deltaz / stepScale) * sp.walk_interp // divisor = stepScale (BN garbled; ACE)
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if interp >= sp.walk_interp || interp < −0.1 → COLLIDED
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contactPt = (s0.center.x, s0.center.y, s0.center.z + deltaz − s0.radius)
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ci.set_contact_plane(Plane(n=(0,0,1), d=−contactPt.z), is_water=1) // §7
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ci.contact_plane_cell_id = sp.check_pos.objcell_id
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sp.walk_interp = interp
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sp.add_offset_to_check_pos((0,0,deltaz))
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return ADJUSTED
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```
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This is THE missing piece that made step-up-onto-a-wide-cylinder impossible:
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`CTransition::step_up`'s internal step-down probe needs branch 2 to produce a
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walkable contact plane ON the cylinder top.
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## 5. normal_of_collision (0x0053ab50)
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```
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normal_of_collision(cyl, sp, sphere, dispCheck, radsum, sphereNum, out n) → bool definite:
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dispCurr = sp.global_curr_center[sphereNum] − low_pt
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if (radsum² < dispCurr.x² + dispCurr.y²): // curr was XY-OUTSIDE → side hit
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n = (dispCurr.x, dispCurr.y, 0) // radial, horizontal
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// definite unless the contact could actually be a diagonal cap hit:
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zBandOverlapAtCurr = |halfH − dispCurr.z| <= sphere.radius − F_EPSILON + halfH
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noZMovement = |dispCurr.z − dispCheck.z| <= F_EPSILON
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return zBandOverlapAtCurr || noZMovement
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// curr was XY-INSIDE the footprint → cap hit
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n = (0, 0, (dispCheck.z − dispCurr.z <= 0) ? +1 : −1) // descending → top (+1)
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return true
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```
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Cap polarity settled by ACE + geometry (BN's x87 branch rendering is
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untrustworthy here — [[feedback_bn_decomp_field_names]] class 2).
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## 6. step_sphere_up (0x0053b310) / land_on_cylinder (0x0053b3d0) / slide_sphere (0x0053b2a0)
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```
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step_sphere_up(t, s0, disp0, radsum):
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if (oi.step_up_height < s0.radius + height − disp0.z) // too tall
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→ slide_sphere(t, s0, disp0, radsum, 0)
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definite = normal_of_collision(..., 0, out n)
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if normalize_check_small(n) → COLLIDED
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nWorld = localspace_pos.localtoglobalvec(n) // rotate by the OBJECT's frame
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if CTransition::step_up(t, nWorld) → OK
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else → sp.step_up_slide(t)
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land_on_cylinder(t, s0, disp0, radsum): // airborne foot hit
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normal_of_collision(..., 0, out n)
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if normalize_check_small(n) → COLLIDED
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sp.set_collide(n) // backup + Collide flag
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sp.walkable_allowance = LANDING_Z (0.0871557)
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return ADJUSTED
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slide_sphere(t, sphere, disp, radsum, sphereNum):
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normal_of_collision(..., sphereNum, out n)
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if normalize_check_small(n) → COLLIDED
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return CSphere::slide_sphere(sphere, sp, ci, n, sp.global_curr_center[sphereNum])
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```
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The airborne landing closes through the retry loop: land_on_cylinder
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(ADJUSTED, sets `sp.collide`) → next attempt → branch 5 exact-TOI rests the
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sphere on the top + CP → next attempt → ε-shaved overlap now misses → OK →
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TransitionalInsert Phase 3 `sp.Collide` placement re-test validates on the
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CP → landing completes.
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## 7. collide_with_point (0x0053acb0) — PathClipped / head-sphere hits
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Port per ACE `CylSphere.CollideWithPoint` verbatim (self-contained TOI math):
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non-PerfectClip movers → `set_collision_normal` + COLLIDED. PerfectClip →
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exact time-of-impact reposition (`add_offset_to_check_pos`) + ADJUSTED, with
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the not-definite branch deriving cap-vs-side from the movement.
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## 8. Divergences + settled ambiguities (register-relevant)
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1. **`is_water=1` on cylinder-top contact planes is RETAIL** (literal 1 at
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0x0053aae2 and the branch-5 site; `set_contact_plane` 0x00509d80 stores
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arg3 → `contact_plane_is_water`). Port verbatim; do not "fix".
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2. **ACE bug (do NOT copy):** ACE's grounded head-sphere leg passes the FOOT
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disp to `SlideSphere`; retail 0x0053b843 passes the HEAD disp (`x_2`).
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Retail wins. (Class: [[feedback_bn_decomp_field_names]] #3 — ACE decode
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wrong in a branch ACE rarely exercises.)
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3. **Block offset in branch 5:** retail subtracts the cur→check landblock
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offset; acdream's physics frame is continuous world-space → offset = 0.
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Standing frame adaptation (same as SlideSphere's gDelta note).
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4. **Ethereal targets:** branch 1 returns COLLIDED on overlap even for
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ethereal; passability comes from the caller's Layer-2 override
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(pc:276961-276989, non-static + !step_down → forced OK) plus the #150
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step-down skip. The previous port consumed ObstructionEthereal with an
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early OK before any test — response-equivalent for non-static targets,
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but branch 1 is the faithful shape and also gives placement inserts the
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retail blocked-by-cylinder semantics. Ported faithfully now.
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5. **`normalize_check_small`** = normalize; returns true (fail) when |v| < ε
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before normalizing — maps to `LengthSquared() < EpsilonSq` guard.
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6. **step_sphere_up normal rotation:** retail rotates the collision normal by
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the target OBJECT's frame (`localspace_pos` = the object's Position cached
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by the wrapper) before `CTransition::step_up`. For yaw-only AC objects
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this only affects yawed radial normals; ported faithfully via
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`Vector3.Transform(n, obj.Rotation)`.
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## 9. acdream port surface
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`Transition.CylinderCollision` (TransitionTypes.cs) becomes the branch-4/5
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dispatcher body; new private siblings `CylCollidesWithSphere`,
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`CylNormalOfCollision`, `CylStepSphereUp`, `CylStepSphereDown`,
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`CylSlideSphere`, `CylLandOnCylinder`, `CylCollideWithPoint`. Callers
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unchanged (`FindObjCollisionsInCell` Cylinder branch; the BspOnlyDispatch
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gate and the #150 ethereal step-down skip sit ABOVE this dispatch and are
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unaffected). `DoStepUp` (= CTransition::step_up, A6.P6) and
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`SpherePath.StepUpSlide` are reused as-is.
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