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feat(physics): Transition.FindTransitionalPosition core algorithm

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Port FindTransitionalPosition, TransitionalInsert, FindEnvCollisions,
AdjustOffset, DoStepDown, ValidateTransition from transition_pseudocode.md.
Outdoor terrain collision with step-down ground contact. Indoor BSP and
object collision deferred to subsequent tasks.

Also adds PhysicsEngine.SampleTerrainZ() which dispatches the terrain Z
query to the right registered landblock by world-space XY position.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
This commit is contained in:
Erik 2026-04-13 23:52:45 +02:00
parent 9ea8ae5191
commit e08a06ac5b
3 changed files with 836 additions and 3 deletions
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18
src/AcDream.Core/Physics/PhysicsEngine.cs
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@ -47,6 +47,24 @@ public sealed class PhysicsEngine
/// </summary>
public void RemoveLandblock(uint landblockId) => _landblocks.Remove(landblockId);
/// <summary>
/// Sample the outdoor terrain Z at the given world-space XY position.
/// Searches all registered landblocks; returns null if no landblock covers the position.
/// Used by Transition.FindEnvCollisions for terrain collision resolution.
/// </summary>
public float? SampleTerrainZ(float worldX, float worldY)
{
foreach (var kvp in _landblocks)
{
var lb = kvp.Value;
float localX = worldX - lb.WorldOffsetX;
float localY = worldY - lb.WorldOffsetY;
if (localX >= 0f && localX < 192f && localY >= 0f && localY < 192f)
return lb.Terrain.SampleZ(localX, localY);
}
return null;
}
/// <summary>
/// Resolve an entity's movement from <paramref name="currentPos"/> by
/// applying <paramref name="delta"/> (XY only) and computing the correct Z