In this lesson, you will learn how to capture and analyze frame data using Unreal Insights to pinpoint exactly which rendering passes are causing your GPU to lag.
While standard statistics like stat unit tell you that your GPU is under pressure, they don’t explain why. Unreal Insights provides a frame-by-frame breakdown, allowing you to see if your bottleneck stems from complex shadow rendering, post-processing, or heavy draw calls.
Capturing the Data
To start, you must launch your project with tracing enabled. You can do this via the command line when launching the editor:
UnrealEditor.exe "YourProject.uproject" -trace=gpu,render
Once the project is open, open the Unreal Insights application (located in your Engine installation folder under Binaries/Win64/UnrealInsights.exe). As you play in the editor or run your standalone build, the tool will record a live stream of data.
Analyzing the GPU Timeline
Once you have a capture, look at the Timing Insights tab. Focus on the GPU track. You will see colored blocks representing different rendering stages like BasePass, ShadowDepths, or PostProcessing.
If you see a specific block—for example, ShadowDepths—taking up a disproportionately large slice of your frame time, you’ve found your culprit. By selecting a specific frame in the timeline, the Details panel will show you the exact duration of each draw call and GPU event. If you see a spike during PostProcessing, you can cross-reference this with the post-processing optimization techniques you learned in previous lessons to see if, for instance, a specific LUT or motion blur setting is becoming too expensive for your target hardware.
Using the Trace Command
You can also trigger a trace during gameplay using the console command:
trace.send gpu,render
This allows you to capture performance data during intense sequences, such as a stormy weather event or a dense volumetric cloud setup, ensuring you identify bottlenecks exactly when they occur. By identifying the specific "hot" blocks, you can iterate on your materials or light settings rather than guessing where the performance is bleeding.
Key Takeaway: Unreal Insights turns guesswork into data-driven optimization by visualizing the GPU timeline, allowing you to isolate and resolve the specific rendering passes causing frame-rate hitches.