Rendering Performance

Start from measured evidence

Use unreal-insights-profiling first when no trustworthy bound/pass/capture exists. Read references/diagnostic-selector.md and references/budgets-and-baselines.md.

1. Lock target hardware, renderer, resolution, quality tier, scene/camera, and frame budget.
2. Identify whether the cost is Render/RHI-thread submission, GPU pass time, GPU memory, or a hitch.
3. Name the largest measured pass/resource/submission category and its millisecond or byte cost.
4. Use the subsystem visualization/stats to locate causal content or settings.
5. Choose the least destructive lever that changes the measured cost: visibility, workload count, quality, resolution, representation, update frequency, or feature path.
6. Change one lever, capture the identical workload, and compare cost plus visual/gameplay impact.
7. Encode approved changes in scalability/device profiles and test every supported tier.

Load only what applies:

• references/resolution-tsr-and-dynamic-resolution.md
• references/nanite-geometry.md
• references/lumen-and-reflections.md
• references/virtual-shadow-maps.md
• references/megalights.md
• references/materials-translucency-and-overdraw.md
• references/submission-culling-and-lods.md
• references/scalability-and-device-profiles.md
• references/gpu-memory-and-resources.md
• references/symptom-recipes.md

Hard rules

• Do not prescribe renderer CVars from symptoms alone; require a measured pass or bounded experiment.
• Do not compare GPU captures at different resolution, screen percentage, camera, or warm/cold state.
• Optimize milliseconds, not triangle/draw-call/instruction counts in isolation.
• Treat editor view modes and visualization overlays as diagnostic overhead; disable them for final timing.
• Preserve gameplay readability and fairness across tiers; scalability must not hide actionable content.
• Prefer scalability groups and device profiles over scattered runtime CVars.
• Treat Lumen Lite as Beta in UE 5.8 and Primitive Debugger/Nanite Foliage as Experimental.
• MegaLights is Production Ready in UE 5.8, but its quality still degrades as per-pixel light complexity exceeds its fixed sampling budget.
• Nanite does not make materials, masked overdraw, WPO, shadows, streaming, or storage free.
• Dynamic resolution mitigates GPU spikes; it does not repair a CPU/render-thread bottleneck.
• Preserve a supported fallback for target platforms that lack Nanite/Lumen/TSR/hardware ray tracing.

See references/sources.md for the UE 5.8 primary-source trail.