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fix(app): Phase A.1 — encode landblock IDs with 0xFFFF terminator, not 0xFFFE

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ROOT CAUSE of the "giant ball with spikes" terrain corruption that
the previous two hotfix attempts (lock + synchronous loading) failed
to address. Threading was a red herring all along.

AC dat conventions:
  0xAAAA0xFFFF — LandBlock dat (terrain heightmap)
  0xAAAA0xFFFE — LandBlockInfo dat (static-object metadata)

WorldView.NeighborLandblockIds correctly uses 0xFFFF. My
StreamingRegion.EncodeLandblockId from Phase A.1 Task 1 used 0xFFFE
by mistake. Every streaming load was therefore calling
LandblockLoader.Load with the LandBlockInfo id, which makes
DatCollection ask DatBinReader to read a LandBlock from the
LandBlockInfo file. The reader's internal buffer position lands in
the middle of the wrong file's bytes, ReadBytesInternal asks for an
out-of-range slice, throws ArgumentOutOfRangeException, and the
landblocks that DON'T throw return half-populated LandBlock objects
whose Height[] arrays contain garbage. Garbage Z values render as
the spike pattern.

The kicker: my Task-1 review fix added a test
(Constructor_SmallRadius_IDsMatchEncodingRule) that asserted
Assert.Contains(0x1234FFFEu, region.Visible). The test was passing
because it pinned the wrong value. I literally codified the bug.

Fix: change EncodeLandblockId's terminator from 0xFFFEu to 0xFFFFu
and update the test to assert 0x1234FFFFu. The XML doc on Visible
now explicitly explains the 0xFFFF/0xFFFE distinction so this can't
recur.

The previous two hotfixes (_datLock in c991fb2, synchronous streamer
in 531c9f9) stay in place — _datLock is defensive belt-and-suspenders
that documents which entry points read dats, and synchronous loading
is correct-by-default until we decide whether to reintroduce
background loading (Phase A.3 may make it unnecessary anyway).

212 tests green. With this fix the streaming should actually work.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
This commit is contained in:
Erik 2026-04-11 22:59:21 +02:00
parent 531c9f9349
commit f83a8c1674
2 changed files with 31 additions and 8 deletions
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12
tests/AcDream.Core.Tests/Streaming/StreamingRegionTests.cs
View file

@ -103,11 +103,17 @@ public class StreamingRegionTests
[Fact]
public void Constructor_SmallRadius_IDsMatchEncodingRule()
{
// Verify EncodeLandblockId is correct (not swapped shifts).
// radius=0 at (0x12, 0x34) → exactly one entry, id = 0x1234FFFE.
// Verify EncodeLandblockId emits the LandBlock terminator (0xFFFF),
// not the LandBlockInfo terminator (0xFFFE). The earlier version of
// this test pinned 0xFFFE and codified the bug that produced "ball
// of spikes" terrain in Phase A.1's first live run — LandblockLoader
// was being asked to read the LandBlockInfo file as a LandBlock,
// which corrupted the dat reader's buffer position and returned a
// half-populated heightmap. radius=0 at (0x12, 0x34) → exactly one
// entry, id = 0x1234FFFF.
var region = new StreamingRegion(cx: 0x12, cy: 0x34, radius: 0);
Assert.Single(region.Visible);
Assert.Contains(0x1234FFFEu, region.Visible);
Assert.Contains(0x1234FFFFu, region.Visible);
}
}