fix(landscape): fail more gracefully when there are no occupied parcels

[AnsisMalins]

Pull Request Description

What does this PR change?

This change adds input validation code in terrain generation so that more informative error messages are logged and the game proceeds with less breakage.

Test Instructions

Visit empty parcels in Genesis City and in worlds and see that the terrain is correct. In particular, test

• teleport from city to world
• teleport from world to city
• teleport from world to world

Quality Checklist

• Changes have been tested locally
• Documentation has been updated (if required)
• Performance impact has been considered
• For SDK features: Test scene is included

Code Review Reference

Please review our Code Review Standards before submitting.

[github-actions]

Windows and Mac build successful in Unity Cloud! You can find a link to the downloadable artifact below.

Name	Link
Commit	830c543
Logs	https://github.com/decentraland/unity-explorer/actions/runs/23787593419
Download Windows	https://github.com/decentraland/unity-explorer/suites/62734397521/artifacts/6195693459
Download Windows S3	https://explorer-artifacts.decentraland.org/@dcl/unity-explorer/branch/fix/zero-owned-parcels/pr-20436-830c543/Decentraland_windows64.zip
Download Mac	https://github.com/decentraland/unity-explorer/suites/62734397521/artifacts/6195662879
Download Mac S3	https://explorer-artifacts.decentraland.org/@dcl/unity-explorer/branch/fix/zero-owned-parcels/pr-20436-830c543/Decentraland_macos.zip
Built on	2026-03-31T09:00:35Z

[claude]

Claude finished @AnsisMalins's task in 1m 37s —— View job

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Code Review

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• Read changed files
• Analyze diff
• Post review

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No blocking issues found. The changes correctly handle the zero-occupied-parcels edge case across all three files.

Summary of changes:

• TerrainModel.cs — CalculateMinMaxParcels returns sentinel (int2(0,0), int2(-1,-1)) when empty, yielding sizeInParcels = (0,0) so terrain is centered at origin with size 2 × borderPadding. This is graceful.
• TerrainGenerator.cs — CreateOccupancyMap returns null early (with a LogWarning) when ownedParcels.IsEmpty; callers already handle null by setting OccupancyMapSize = 0 and an empty NativeArray.
• WorldTerrainGenerator.cs — Same null-handling pattern added consistently.

Traced the flat-terrain guarantee:
When no occupied parcels → OccupancyMap = null → OccupancyMapSize = 0 → GetParcelNoiseHeight uses occupancy = 0f. Both possible OccupancyFloor values (0 or 255) satisfy occupancy (0f) <= minValue, returning 0f. Flat terrain, as expected. ✓

One minor observation (no fix required):
CalculateMinMaxParcels returning (0,0)/(-1,-1) when borderPadding = 0 leads to sizeInParcelsWithPadding = (0,0), which causes Mathf.ClosestPowerOfTwo(0) = 0 and zero-sized chunks. This is a pre-existing edge case that is not worsened by this PR, and in practice borderPadding > 0 in all known configurations.

REVIEW_RESULT: PASS ✅
COMPLEXITY: SIMPLE

[github-actions]

Auto-approved by Claude — simple fix/chore with no blocking issues. QA approval is still required.

[AnsisMalins]

PR 7954

PR number: 7954
Windows change build
Windows baseline build
macOS change build
macOS baseline build

Intel Core i3

Change samples: 2670
Baseline samples: 2672

Metric	Change	Baseline	Delta	Improvement
CPU average	33.6 ms	33.6 ms	0.0 ms	-0.0%	⚪
CPU 1% worst	54.6 ms	56.5 ms	-1.9 ms	3.4%	🟢
CPU 0.1% worst	115.2 ms	116.1 ms	-0.8 ms	0.7%	⚪
GPU average	16.1 ms	15.6 ms	0.5 ms	-3.2%	🔴
GPU 1% worst	21.8 ms	21.5 ms	0.3 ms	-1.3%	⚪
GPU 0.1% worst	25.2 ms	27.3 ms	-2.2 ms	8.0%	🟢