Layout and Build times don't add up

[jacob314]

Here the frame took 160ms but build+layout is over 300ms. Looking at the timeline, It seems like the value for build is calculated incorrectly or the two times can overlap due to cascading builds and layouts and we need to factor that into the UI to not double count.

Repro json file.
dart_devtools_2022-09-23_09:03:04.681.json.txt

[kenzieschmoll]

We don't do any calculating for the times in the flutter frames chart. We pull these times directly from the 'Flutter.Frame' events. So if the timeline events and the Flutter.Frame events show drastically different build times, I would think the time calculation in the Framework is incorrect (@goderbauer @iskakaushik)

[goderbauer]

Does the code in question here use a LayoutBuilder or a lazy list? Both nest build phases within the layout phase. So, you can't just add build and layout times to get the total frame time.

[srawlins]

Closing as resolved / working as intended. As explained by the Flutter team, widgets such as LayoutBuilder and lazy lists nest build phases within layout, meaning build and layout times can overlap and cannot simply be summed together. DevTools displays the build and raster durations directly reported by the Flutter engine's Flutter.Frame events, and the DevTools Frame Analysis tab already subtracts nested build event durations from layout time.