RND-SET-001: Rendering Settings Audit

What This Rule Detects

This rule audits project-wide rendering settings and flags potentially expensive feature combinations:

• Lumen Global Illumination: Dynamic GI with significant GPU cost
• Lumen Reflections: Screen-space + ray-traced reflection system
• Virtual Shadow Maps (VSM): High-quality shadow system with memory overhead
• Nanite: Virtualized geometry system with setup overhead
• Feature combinations: Lumen + VSM + Nanite together compound cost

The default threshold is a risk score of 2.5 before flagging.

Why This Matters

Epic’s Published Lumen Budgets

Epic’s performance guidance provides concrete budget targets for Lumen:

UE 5.5’s official release notes state Lumen can run at 60 Hz on platforms with hardware ray tracing support due to HWRT improvements.

Fallback warning: If hardware ray-tracing is unavailable, Lumen switches to software ray-tracing which costs 8-15ms instead of 3-4ms. Verify on your target GPU.

VSM: Physical Page Pool Concept

Virtual Shadow Maps store shadow data for all lights in a single large texture pool. From Epic’s documentation:

• VSM uses a “physical page pool” for shadow storage
• Pool can overflow with many lights or large shadow distances
• Overflow causes quality artifacts or missing shadows
• VRAM pressure increases with shadow quality settings

Typical VRAM usage: 200-500MB for shadow atlas depending on quality settings.

Resolution Scaling Impact

These costs scale with resolution:

AMD’s GPUOpen guidance reports Lumen software vs hardware RT can differ by ~1.2ms on a Radeon 7900 XTX—“one checkbox” can be a measurable budget swing.

Memory Pressure: VSM uses significant GPU memory for shadow data. Nanite stores mesh data in GPU-visible memory. Combined, they can consume 1-2GB+ VRAM.

Platform Compatibility: Mobile, Switch, and older consoles may not support these features. Projects targeting them should disable or configure alternatives.

Real Example: A project enables Lumen GI, Lumen Reflections, VSM, and Nanite. On an RTX 3070, base rendering cost is 10ms (60fps ceiling). Add 100 Nanite meshes, dynamic lights, and gameplay—frame rate drops below 30.

When This Is Acceptable

• High-end PC exclusive: Targeting RTX 3080+ or equivalent
• Scalability configured: Quality levels disable features for lower specs
• Profiled on target hardware: Measured and accepted the baseline cost
• Artistic requirement: Lumen GI is essential to the visual style

The Problem

Feature Combination Risk

Project Rendering Settings Analysis

Lumen Global Illumination: ENABLED   → +1.0 risk
Lumen Reflections: ENABLED           → +0.5 risk
Virtual Shadow Maps: ENABLED         → +1.0 risk
Nanite: ENABLED                      → +1.0 risk

Combinations:
Lumen GI + VSM: +0.75 risk (both compete for GPU)
Lumen GI + Nanite: +0.50 risk (both use compute)

Total Risk Score: 4.75 (threshold: 2.5) = CRITICAL
Estimated Baseline: ~0.90ms × 4.75 ≈ 4.3ms

GPU Budget Context

The Fix

Option 1: Configure Scalability Levels

Create quality tiers that disable expensive features on lower specs:

Engine/Config/DefaultScalability.ini:

[GlobalIlluminationQuality@0]
r.DynamicGlobalIlluminationMethod=0  ; None

[GlobalIlluminationQuality@1]
r.DynamicGlobalIlluminationMethod=1  ; Screen Space

[GlobalIlluminationQuality@2]
r.DynamicGlobalIlluminationMethod=2  ; Lumen

[ShadowQuality@0]
r.Shadow.Virtual.Enable=0  ; Traditional shadows

[ShadowQuality@2]
r.Shadow.Virtual.Enable=1  ; VSM

Option 2: Disable Lumen for Non-Essential Projects

If your project doesn’t require dynamic GI:

Project Settings → Rendering:

1. Dynamic Global Illumination Method → None or Screen Space
2. Reflection Method → Screen Space

Alternatives to Lumen GI:

• Baked lightmaps for static scenes
• Light Propagation Volumes for specific use cases
• Screen Space GI for subtle bounce light

Option 3: Use VSM Selectively

VSM excels for specific scenarios:

Enable VSM when:

• Many dynamic/movable lights
• Large open worlds
• Cinematic quality shadows needed

Disable VSM when:

• Mostly static lighting
• Interior-focused levels
• Targeting older hardware

Project Settings → Rendering:

• Shadow Map Method → Shadow Maps (traditional) or Virtual Shadow Maps

Option 4: Nanite Per-Mesh Control

Don’t enable Nanite globally if only some meshes benefit:

Keep Nanite off by default:

1. Project Settings → Rendering → Nanite → Default Nanite Enabled = Off

Enable per-mesh:

1. Open high-detail Static Mesh
2. Check Enable Nanite Support
3. Leave simple meshes with traditional LODs

This avoids Nanite overhead on meshes that don’t need it.

Option 5: Platform-Specific Rendering Paths

Configure different settings per platform:

Config/Windows/WindowsEngine.ini:

[/Script/Engine.RendererSettings]
r.DynamicGlobalIlluminationMethod=2
r.Shadow.Virtual.Enable=True
r.Nanite.ProjectEnabled=True

Config/Switch/SwitchEngine.ini:

[/Script/Engine.RendererSettings]
r.DynamicGlobalIlluminationMethod=0
r.Shadow.Virtual.Enable=False
r.Nanite.ProjectEnabled=False

Option 6: Profile and Document Budget

If you intentionally use expensive features, document the decision:

1. Profile on lowest supported hardware
2. Document baseline rendering cost
3. Set gameplay feature budgets based on remaining frame time
4. Accept the finding in Blueprint Health Analyzer with justification

Feature Compatibility Matrix

Checking Current Settings

Via Console Commands:

r.DynamicGlobalIlluminationMethod   ; 0=None, 1=SSGI, 2=Lumen
r.ReflectionMethod                   ; 0=None, 1=SSR, 2=Lumen
r.Shadow.Virtual.Enable              ; 0=Off, 1=On
r.Nanite.ProjectEnabled              ; 0=Off, 1=On

Via Project Settings: Project Settings → Engine → Rendering → Global Illumination / Shadows / Nanite

Performance Profiling

Key stats for rendering features:

stat GPU                  ; Overall GPU timing
stat Lumen                ; Lumen-specific costs
stat ShadowRendering      ; Shadow map costs
stat Nanite               ; Nanite geometry costs
ProfileGPU                ; Detailed GPU profiler

Configuration

Threshold: Risk score before flagging (default: 2.5)

To adjust in Project Settings:

Blueprint Health Analyzer → Rule Thresholds → RND-SET-001 → 4.0

Higher thresholds for projects targeting high-end hardware exclusively. Lower thresholds (1.5) for projects that must scale to older hardware.

Related Rules

• AST-MESH-001 - Mesh optimization interacts with Nanite
• MAT-INST-001 - Material complexity compounds rendering cost
• NIA-GPU-001 - VFX compete with rendering features for GPU time