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Zone.Update takes every previous position before placing any orbit

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GetOrbitPosition places a parent as a side effect of placing its child, so with a child listed first the parent's previous position was already its new one and its Velocity came out zero. The constructor's unread PreviousPosition write is dropped; the first Update takes it from the placed Position. The velocity test now runs moon-first and planet-first packs over varying dt. Builds not verified yet (verify follows).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
This commit is contained in:
Meta Vens 2026-10-14 21:19:09 +02:00
commit 205098ef93
2 changed files with 26 additions and 13 deletions
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7
Assets/Scripts/ServerShared/Zone.cs
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@ -165,7 +165,7 @@ public class Zone
// when the zone is built, so each well, light and body pose read before the first Update is where the
// body is. Velocity stays zero until the first Update differences two placed positions.
foreach (var orbit in Orbits)
orbit.Value.PreviousPosition = GetOrbitPosition(orbit.Key);
GetOrbitPosition(orbit.Key);
foreach (var body in pack.Planets)
{
@ -276,9 +276,12 @@ public class Zone
{
_time += deltaTime;
_updatedOrbits.Clear();
// Every previous position is taken before any orbit is placed: GetOrbitPosition places a parent as a
// side effect of placing its child, so differencing inside one loop would depend on dictionary order.
foreach (var orbit in Orbits)
orbit.Value.PreviousPosition = orbit.Value.Position;
foreach (var orbit in Orbits)
{
orbit.Value.PreviousPosition = orbit.Value.Position;
orbit.Value.Position = GetOrbitPosition(orbit.Key);
orbit.Value.Velocity = (orbit.Value.Position - orbit.Value.PreviousPosition) / deltaTime;
}

32
tests/Aetheria.Shared.Tests/ZonePlacedAtBuildTests.cs
View file

@ -60,7 +60,7 @@ public sealed class ZonePlacedAtBuildTests : IDisposable
public CultRecordKey PlanetOrbit;
}
private Scene Build(float phase, double time)
private Scene Build(float phase, double time, bool moonFirst = false)
{
var dir = Path.Combine(_root, $"zone{_caches.Count}");
Directory.CreateDirectory(dir);
@ -78,15 +78,21 @@ public sealed class ZonePlacedAtBuildTests : IDisposable
{
Parent = new CultRecordRef<OrbitData>(rootOrbit), Distance = Distance, Phase = phase
}).Key;
var moonOrbit = cache.Upsert(new OrbitData
{
Parent = new CultRecordRef<OrbitData>(planetOrbit), Distance = 100f
}).Key;
var planet = cache.Upsert(new PlanetData { Orbit = new CultRecordRef<OrbitData>(planetOrbit), Mass = 1f }).Key;
var pack = new ZonePack
{
Orbits = { new CultRecordRef<OrbitData>(rootOrbit), new CultRecordRef<OrbitData>(planetOrbit) },
Planets = { new CultRecordRef<BodyData>(planet) },
Radius = 5000f,
Mass = 10000f,
Time = time
};
// The same three orbits either way; only the order the pack lists them in differs.
var listed = moonFirst ? new[] { moonOrbit, planetOrbit, rootOrbit } : new[] { rootOrbit, planetOrbit, moonOrbit };
foreach (var key in listed) pack.Orbits.Add(new CultRecordRef<OrbitData>(key));
var zone = new Zone(items, Settings(), pack, new GalaxyZone { Name = "Placed", Owner = null }, null);
return new Scene { Cache = cache, Items = items, Hull = hull, Zone = zone, PlanetOrbit = planetOrbit };
}
@ -104,7 +110,6 @@ public sealed class ZonePlacedAtBuildTests : IDisposable
var expected = RootAt + OrbitData.Evaluate(frac(turns + phase)) * Distance;
Assert.InRange(length(orbit.Position - expected), 0f, .01f);
Assert.InRange(length(orbit.PreviousPosition - expected), 0f, .01f);
// The well pulls toward the body's place: a point 30 u east of it is pushed west.
var force = s.Zone.GetForce(expected + new float2(30f, 0f));
@ -112,16 +117,21 @@ public sealed class ZonePlacedAtBuildTests : IDisposable
Assert.InRange(normalize(force).x, -1f, -.99f);
}
[Fact]
public void TheFirstTickVelocityIsTheOrbitsSpeed()
// A parent's velocity is its own orbital velocity on the first tick and every tick after, whichever order
// the pack lists a moon and its planet in. dt differs per tick so a velocity taken from a fixed step fails.
[Theory]
[InlineData(false)]
[InlineData(true)]
public void TheFirstTickVelocityIsTheOrbitsSpeed(bool moonFirst)
{
var s = Build(.35f, 0.0);
const float dt = 1f / 60f;
s.Zone.Update(dt);
var speed = length(s.Zone.Orbits[s.PlanetOrbit].Velocity);
var s = Build(.35f, 0.0, moonFirst);
var expected = 2f * PI * Distance / Period;
Assert.InRange(speed, expected * .99f, expected * 1.01f);
foreach (var dt in new[] { 1f / 60f, 1f / 30f, 1f / 60f })
{
s.Zone.Update(dt);
var speed = length(s.Zone.Orbits[s.PlanetOrbit].Velocity);
Assert.InRange(speed, expected * .99f, expected * 1.01f);
}
}
[Fact]