Worldgen Phase 1: tune dry biome terrain modifiers

[MichaelFisher1997]

Parent: #646

Phase

Phase 1: Terrain modifier integration

Goal

Make desert, savanna, plateau, and badlands terrain more structurally distinct.

Tasks

• Tune desert, savanna, savanna_plateau, windswept_savanna, badlands, wooded_badlands, and eroded_badlands modifiers.
• Bias plateaus/badlands toward stronger relief without overwhelming all hot/dry terrain.
• Preserve reasonable traversal in common desert/savanna areas.
• Add baseline comparisons for hot/dry biome height and ruggedness.

Acceptance Criteria

• Badlands and plateaus have a stronger terrain identity than desert/plains.
• Common hot/dry areas remain playable and not uniformly mountainous.
• Tests/baselines capture intended distribution changes.

Dependencies

• Requires terrain modifier integration.

Parallelization

Can run in parallel with wetland and mountain tuning after integration.

[github-actions]

Analysis Comment:

This is a Feature Request targeting Phase 1 of the biome terrain modifier integration work (parent issue #646).

Scope Assessment:
The issue is well-scoped — focused exclusively on tuning TerrainModifier fields (height_amplitude, smoothing, height_offset) for hot/dry biomes: desert, savanna, savanna_plateau, windswept_savanna, badlands, wooded_badlands, and eroded_badlands.

Current State:
The TerrainModifier struct already exists in modules/world-worldgen/src/biome_registry.zig:56-65 with fields for height_amplitude, smoothing, and height_offset. The hot/dry biomes have these set inconsistently:

• desert — uses defaults (amplitude=1.0, no smoothing)
• savanna — amplitude=0.8, smoothing=0.15
• savanna_plateau — amplitude=0.6, smoothing=0.3, offset=+8.0
• windswept_savanna — amplitude=1.3, no smoothing
• badlands — uses defaults
• wooded_badlands — amplitude=1.0, smoothing=0.1
• eroded_badlands — amplitude=1.8, no smoothing

Issue: The task list has blank placeholders (e.g., "Tune , , , , , , and modifiers.") — the actual modifier names are missing from the issue body. Please clarify: is the intent to tune height_amplitude, smoothing, and height_offset for these seven biomes specifically, or are there additional modifiers referenced in the parent issue that should be included?

Recommended Sub-Tasks:

1. Add baseline height/ruggedness tests for hot/dry biomes before tuning
2. Increase height_amplitude for badlands variants (currently at defaults vs. eroded_badlands at 1.8)
3. Tune savanna_plateau to preserve traversal while maintaining plateau identity
4. Verify desert terrain doesn't become uniformly mountainous with amplitude changes

opencode session  |  github run