Setup
In this chapter, I use the following experimental setup.
If it does not reproduce on your device, please firstly try to use the code of Flutter framework and engine at the time when this benchmark chapter is written. This is because I have made some further experiments and merges after this benchmark, which may break the existing code and I have not tested it (given this is not merged to Flutter yet).
Testing device
All tests are done in a TRT-AL00 Android device, with Snapdragon 435.
How slow is it? Geekbench says it is 642 & 2867 points (single & multi core, respectively). Another rough but intuitive viewpoint is by looking at comments on onReportTimings - Flutter officially says it takes <0.1ms on iPhone6S per second, while I have measured ~20ms per second.
As a side remark, this device has roughly 100ms latency in touching, i.e. Android system will only dispatch a touch event ~100ms after the real touch. This is OS level and Flutter has no way to overcome it.
Testing scenario
A very common case of jank is when scrolling a ListView. Therefore, in this chapter, I use the list-view-scrolling in the example app. (The code may be refactored later, so ping me if the link becomes invalid.)
To mimic the real scenario, when a new ListView item is created, half of them will create 80 child widgets, and each of them takes 1ms to layout. Therefore, for slow scrolling, it will mimic a very heavy content that takes 80ms to layout. For fast scrolling where multiple items are created in one frame, it can be ~160ms, ~240ms etc. (Remark: These numbers may be changed in the future, so please look at code for details.)