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fix(B.4b): WorldPicker.Pick — handle inside-sphere origin + document normalize contract

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Code review flagged two latent correctness bugs in Pick:

1. The single t = -b - sqrt(d) intersection skipped entities whose
   5m bounding sphere contained the ray origin. Realistic at
   point-blank range — if the player stands within ~5m of a door,
   the near-plane sits inside the door's bounding sphere and the
   door becomes unpickable. Standard fix: when t_near < 0 fall
   through to t_far = -b + sqrt(d) (the sphere exit point).

2. The discriminant formula assumes |direction| = 1. BuildRay
   currently normalizes so the assumption holds at the wire, but
   the contract wasn't documented. Added an explicit
   <param name="direction"> note.

New test Pick_RayOriginInsideEntitySphere_StillReturnsServerGuid
covers the inside-sphere case. Suite: 9/9 WorldPicker tests pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
Erik 2026-05-13 17:52:45 +02:00
parent 221b64186d
commit 5821bdc9ea
2 changed files with 31 additions and 2 deletions
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16
src/AcDream.Core/Selection/WorldPicker.cs
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@ -60,6 +60,13 @@ public static class WorldPicker
/// using a fixed 5m sphere radius. Returns the <see cref="WorldEntity.ServerGuid"/>
/// of the closest hit within <paramref name="maxDistance"/>, or null on miss.
/// </summary>
/// <param name="direction">
/// World-space ray direction. <b>Must be normalized</b> — the geometric
/// ray-sphere formula simplifies <c>a = dot(direction, direction)</c> to
/// <c>1</c>; non-unit input produces an undocumented <c>t</c>-scale that
/// makes <c>maxDistance</c> compare against ray-parameter units instead
/// of world meters.
/// </param>
/// <remarks>
/// Entities with <c>ServerGuid == 0</c> (atlas-tier scenery, dat-hydrated
/// statics) are skipped — they have no server-side identity and can't be
@ -94,8 +101,13 @@ public static class WorldPicker
float d = b * b - c;
if (d < 0f) continue;
float t = -b - MathF.Sqrt(d);
if (t < 0f) continue; // ray points away or origin inside
// Two intersection roots: t_near = -b - sqrt(d), t_far = -b + sqrt(d).
// If t_near < 0 the ray origin is INSIDE the sphere; fall through
// to t_far so the entity is still pickable at point-blank range.
float sqrtD = MathF.Sqrt(d);
float t = -b - sqrtD;
if (t < 0f) t = -b + sqrtD; // origin inside sphere -> use far exit
if (t < 0f) continue; // both roots negative -> sphere entirely behind ray
if (t >= maxDistance) continue;
if (t < bestT)
{