MAT-TEX-001: Material Texture Sample Count

What This Rule Detects

This rule flags materials that sample more textures than the configured threshold (default: 12 samples). Each texture sample has a cost in terms of memory bandwidth and GPU texture unit usage.

Why This Matters

Texture Sampling Is Fundamentally About Bandwidth

The cost of texture sampling is fundamentally about memory bandwidth and cache behavior. Each sample fetches texture data from GPU memory, and the cost varies based on:

• Texture format: Larger formats (R16G16B16A16) fetch more bytes per sample
• Mipmap selection: Lower mips reduce bandwidth demands
• Cache hit rate: Repeated samples to nearby UVs are faster
• Filtering mode: Anisotropic filtering samples multiple mips

Platform Bandwidth Budgets

How to estimate: Bandwidth ≈ (pixels × samples × bytes/sample × filter cost) / available bandwidth. When this exceeds capacity, you’re bandwidth-bound.

Texture Unit Limits (Hardware)

GPUs have a limited number of texture units. Exceeding these causes shader stalls:

Real Example: A terrain material with 8 layers, each using diffuse + normal + ORM textures, samples 24+ textures. On mobile, this material may not even compile. On PC, it wastes bandwidth on areas where only 2-3 layers blend.

When This Is Acceptable

• Hero materials: Key character or prop materials where visual quality justifies the cost
• Masked complexity: Material uses static switches to compile out unused samples
• Distance culling: High-detail material only used at close range with simpler LOD fallback

The Problem

M_TerrainMaster (Example breakdown)
├── Layer 1: Diffuse + Normal + ORM    = 3 samples
├── Layer 2: Diffuse + Normal + ORM    = 3 samples
├── Layer 3: Diffuse + Normal + ORM    = 3 samples
├── Layer 4: Diffuse + Normal + ORM    = 3 samples
├── Macro Normal                        = 1 sample
├── Macro Variation                     = 1 sample
├── Detail Normal                       = 1 sample
└── Blend Mask                          = 1 sample
                                        ─────────
                              Total:    16 samples

Even a simple-looking material can accumulate samples quickly when using standard PBR texture sets across multiple layers.

The Fix

Option 1: Pack Textures (Recommended)

Combine related data into fewer textures:

Before (3 textures per material):

T_Rock_Roughness.uasset     (R channel only)
T_Rock_Metallic.uasset      (R channel only)
T_Rock_AO.uasset            (R channel only)

After (1 texture):

T_Rock_ORM.uasset           (R=AO, G=Roughness, B=Metallic)

This reduces 3 texture samples to 1 with no quality loss.

Common packing conventions:

• ORM: Occlusion, Roughness, Metallic
• RMA: Roughness, Metallic, AO
• ARM: AO, Roughness, Metallic (Unreal default)

Option 2: Use Texture Arrays

For materials with many similar textures (terrain layers, decal variants):

1. Combine individual textures into a Texture2DArray
2. Sample once with a layer index
3. Dramatically reduces sample count for layered materials

Before (4 diffuse samples):

Sample Layer1_Diffuse
Sample Layer2_Diffuse
Sample Layer3_Diffuse
Sample Layer4_Diffuse

After (1 array sample):

Sample TerrainDiffuseArray[LayerIndex]

Option 3: Remove Unused Textures

Audit your material for textures that don’t contribute visually:

• Detail normals on surfaces viewed from distance
• Cavity/AO maps when scene AO is sufficient
• Emissive textures with constant zero values
• Alpha textures on opaque materials

Use the Material Editor’s “Window → Statistics” to see actual used textures.

Option 4: Share Textures Across Materials

Create a shared texture library:

Content/
  Textures/
    Shared/
      T_Shared_Noise.uasset
      T_Shared_DetailNormal.uasset
      T_Shared_Grunge.uasset

Instead of duplicating detail/noise textures per material, reference shared ones. This also improves texture streaming efficiency.

Option 5: Use Virtual Texturing

For projects targeting modern platforms, enable Virtual Texturing:

1. Project Settings → Rendering → Enable Virtual Texturing
2. Convert large texture sets to Virtual Textures
3. Reduces effective sample count as VT streams only visible data

Note: Virtual Texturing has its own overhead and is best for large texture atlases, not individual textures.

Option 6: Create LOD Materials

Use simpler materials at distance:

// In mesh LOD settings
LOD0: M_Character_Full    (16 samples - close up)
LOD1: M_Character_Medium  (8 samples - medium)
LOD2: M_Character_Simple  (4 samples - distant)

Configuration

Threshold: Maximum texture sample count (default: 12)

To adjust in Project Settings:

Blueprint Health Analyzer → Rule Thresholds → MAT-TEX-001 → 16.0

Lower thresholds (8) for mobile/VR projects. Higher thresholds (16+) acceptable for high-end PC.

How to Check Texture Sample Count

1. Open the material in Material Editor
2. Go to Window → Statistics (or press Ctrl+Shift+S)
3. Find “Texture Samplers” in the stats
4. Note: Virtual Textures and Texture Arrays count differently

Related Rules

• MAT-INST-001 - Shader instruction budget
• MAT-PERM-001 - Static switch permutation explosion
• AST-TEX-001 - Individual texture health issues