[Batch 4] Expand render distance presets + LOD tuning

[MichaelFisher1997]

Summary

Add "Ultra" (256 chunks) and "Extreme" (512 chunks) render distance presets and tune LOD transition distances, fog curves, and mesh quality per LOD level for each preset.

Depends on: #381 (QEM LOD meshes — need good LOD quality before pushing further)

Current Presets

The settings system (settings/data.zig) has a render distance slider. LOD levels are defined in lod_chunk.zig with configurable radii. Current LOD extends to ~100 chunks max.

Target Presets

Preset	LOD0	LOD1	LOD2	LOD3	Total Distance	Target FPS
Low	8	16	—	—	16 chunks	120+
Medium	16	32	48	64	64 chunks	120+
High	16	32	64	100	100 chunks	60+
Ultra	16	32	64	256	256 chunks	60+
Extreme	16	32	128	512	512 chunks	30+

Per-Preset LOD Tuning

LOD0 (full detail):

• Unchanged: full greedy mesh, all block types, AO, biome colors

LOD1 (2× simplified):

• Target: 25% triangle count via QEM
• Fog start: 50% of LOD1 radius
• No cutout/transparent blocks (vegetation → solid green)

LOD2 (4× simplified):

• Target: 12% triangle count via QEM
• Fog start: 40% of LOD2 radius
• No fluids, no cutout — everything rendered as solid
• Reduced AO precision

LOD3 (8× simplified):

• Target: 3% triangle count (~200 triangles per region)
• Fog start: 30% of LOD3 radius
• Heightmap-quality: single top-face color per column
• No lighting — flat biome colors

Fog Curves

• Exponential fog starting at configurable % of LOD radius
• Fog color lerps from atmospheric scattering color to sky horizon color
• LOD3 should fade smoothly into sky (no hard cutoff)
• "Extreme" preset: LOD3 uses aggressive fog to mask low detail

Implementation Plan

Step 1: New preset definitions

• Add "Ultra" and "Extreme" to settings choice list
• Define LOD radii, fog parameters, and quality targets per preset
• Store in render_settings.zig as typed config structs

Step 2: Expose LOD config in settings

• Add LOD-related settings to settings/data.zig:
  • lod_cell_size: f32 (default per preset)
  • lod_propagation_distance: f32
  • fog_start_percent: f32 per LOD level
• These appear in the graphics settings screen

Step 3: LOD distance tuning

• LODConfig in lod_chunk.zig gets radii from current preset
• LODManager reads config on preset change and recalculates
• Ensure smooth transitions when render distance changes

Step 4: LOD quality degradation

• LOD2: skip cutout/fluid passes, render vegetation as solid with biome color
• LOD3: skip all lighting, use flat biome colors from BiomeColorProvider
• These are mesh-time decisions in LODMesh build path

Step 5: Warning for Extreme preset

• Show "WARNING: Extreme render distance may cause instability on GPUs with <8GB VRAM"
• Detect VRAM via Vulkan device properties
• Allow override via settings

Files to Modify

• src/game/settings/data.zig — new presets, LOD settings fields
• src/engine/graphics/render_settings.zig — preset definitions
• src/world/lod_chunk.zig — LODConfig updated with new radii
• src/world/lod_manager.zig — read config, recalculate
• src/world/lod_mesh.zig — quality degradation per LOD level
• src/game/screens/graphics.zig — show new presets, LOD settings

Testing

• Each preset loads and renders without crashes
• LOD transitions are smooth (no popping visible from camera)
• Fog hides LOD transitions naturally
• VRAM usage stays within bounds for each preset
• "Ultra" runs at 60+ FPS on RTX 3060 at 256 chunks
• Extreme preset shows warning on low-VRAM devices

Roadmap: docs/PERFORMANCE_ROADMAP.md — Batch 4, Issue 3C

[opencode-agent]

Based on my analysis of the codebase, here's my assessment:

Classification: Feature Request

Current State Analysis:

• render_distance is currently limited to 2-32 chunks (src/game/settings/data.zig:134)
• LOD radii are hardcoded to {16, 40, 80, 160} (src/world/lod_chunk.zig:326)
• LOD system has 4 levels with ILODConfig interface already designed for configurability

Key Findings:

1. Blocked by dependency: Issue [Batch 3] Integrate quadric decimation into LOD mesh pipeline #381 (QEM LOD meshes) must be completed first - the LOD quality degradation specs (25%, 12%, 3% triangle counts) depend on QEM being implemented.

2. Scope considerations: This is a substantial change touching 5+ files across settings, LOD, and UI subsystems. However, it's a cohesive feature (expand render distance with proper LOD), so keeping it as one issue is reasonable.

3. Current limitation: The render distance slider max (32) is far below the requested 256/512 chunks. This will require either:

   • Changing the slider to use preset-based selection instead of raw chunk count
   • Or decoupling the UI slider from the actual render distance when presets are used

Questions for clarification:

1. Is [Batch 3] Integrate quadric decimation into LOD mesh pipeline #381 (QEM LOD meshes) completed? This issue is blocked until that's merged.
2. What's the expected VRAM usage at 256 and 512 chunks? With current chunk data structures, this could be 4-8GB+ just for terrain data.
3. Should the existing render_distance slider be replaced entirely with preset selection, or should presets override the slider value?

Recommended approach:
Wait for #381 completion, then implement in 2 phases:

• Phase 1: Preset definitions + settings infrastructure
• Phase 2: LOD quality degradation + fog tuning per preset

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