MAT-INST-001: Material Instruction Budget

What This Rule Detects

This rule flags materials whose compiled shader instruction count exceeds the configured threshold (default: 350 instructions). Higher instruction counts mean more GPU work per pixel, which directly impacts frame rate.

Why This Matters

Instruction Counts Are a Proxy Signal

Shader instruction counts are not a direct “milliseconds” measurement—they’re a proxy signal that correlates with “more work per pixel.” The actual GPU cost depends on:

• Screen coverage: How many pixels run this shader?
• Overdraw: How many times is each pixel rendered?
• Memory bandwidth: Are texture fetches the bottleneck instead?
• GPU architecture: Different GPUs execute shaders differently

Community shader optimization guidance explicitly treats instruction counts as a useful first look at material complexity, not a definitive cost measurement.

The Visibility Axis (GPU)

Instruction count matters most when the material covers significant screen area:

A “cheap” material is one where the expensive work is not executed for most pixels, or is moved to less frequent paths (LOD), or is baked into textures.

Platform Instruction Budgets

These are per-material budgets. A scene with multiple complex materials covering screen compounds the cost.

Real Example: A layered terrain material with 8 texture layers, height blending, wetness, and detail normals can easily hit 600+ instructions. On a landscape covering most of the screen, this becomes the dominant GPU cost—potentially 3-5ms on current-gen consoles.

When This Is Acceptable

• Hero materials: Character faces, key props, or signature assets where visual quality justifies the cost
• Small screen coverage: Materials that only appear on small objects or limited screen area
• LOD fallback exists: High-detail material at LOD0 with simpler versions at distance
• Already profiled: You’ve verified GPU performance on target hardware and have headroom

The Problem

M_TerrainMaster
├── Layer Blend (8 layers)           → 80+ instructions
├── Height Blend per layer           → 120+ instructions
├── Detail Normal per layer          → 60+ instructions
├── Wetness calculation              → 40+ instructions
├── Distance-based tiling            → 30+ instructions
└── Macro variation                  → 50+ instructions
                                      ─────────────────
                            Total:    380+ instructions

The shader compiler shows you instruction counts in the Material Editor stats panel. When this number exceeds your budget, the material becomes a performance risk.

The Fix

Option 1: Use Material Instances with Static Switches (Recommended)

Move optional features behind static switch parameters, then create instances with only needed features enabled:

Parent Material:

Use Wetness? [Static Switch] → Wetness logic
Use Detail Normal? [Static Switch] → Detail sampling
Use Macro Variation? [Static Switch] → Macro logic

Instances:

• MI_Terrain_Full - All features (hero areas)
• MI_Terrain_Simple - No wetness/macro (background)
• MI_Terrain_Distant - No detail normal (LOD)

Static switches compile out unused paths entirely, reducing instructions in the final shader.

Option 2: Simplify Layer Blending

Replace height-blend with simple lerps where the quality difference isn’t visible:

Before (expensive):

HeightLerp(Layer1, Layer2, HeightMap, Blend, Contrast)

After (cheap):

Lerp(Layer1, Layer2, BlendMask)

Height blending adds 15-20 instructions per layer transition. Simple lerps cost 1-2 instructions.

Option 3: Reduce Texture Samples

Combine related data into fewer textures:

• Pack Roughness, Metallic, AO into RGB channels of one texture
• Use Packed ORM textures instead of separate maps
• Share textures between similar materials via Material Layers

Each texture sample costs 4-8 instructions plus memory bandwidth.

Option 4: Create LOD Materials

Use simpler materials at distance where detail isn’t visible:

1. Create a “Simple” material variant without expensive features
2. In the mesh’s LOD settings, assign the simple material to LOD1+
3. Or use Material Quality switches to reduce complexity on lower quality settings

Option 5: Move to Material Layers

For complex materials, Material Layers let you:

• Share common logic (saves compilation time)
• Swap layers per-instance
• Reduce redundant instructions across materials

Configuration

Threshold: Maximum shader instruction count (default: 350)

To adjust in Project Settings:

Blueprint Health Analyzer → Rule Thresholds → MAT-INST-001 → 500.0

Higher thresholds are appropriate for PC-only projects. Lower thresholds (200-250) are recommended for mobile or VR.

How to Check Instruction Count

1. Open the material in the Material Editor
2. Look at the Stats panel (Window → Stats if not visible)
3. Find “Pixel Shader Instructions” for the base pass
4. Note: Different shader permutations may have different counts

The analyzer uses a representative instruction count that accounts for common material configurations.

Related Rules

• MAT-PERM-001 - Static switch permutation explosion
• MAT-TEX-001 - Texture sample count budget