The timeline view displays information about Flutter frames. It consists of three parts, each increasing in granularity:
Use a profile build of your application to analyze performance. Frame rendering times are not indicative of release performance unless your application is run in profile mode.
This chart is populated with individual frames as they are rendered in your application. Each bar in the chart represents a frame. The bars are color-coded to highlight the different portions of work that occur when rendering a Flutter frame: work from the UI thread and work from the GPU thread.
Clicking a bar will display additional details about the frame.
The UI thread executes Dart code in the Dart VM. This includes code from your application as well as the Flutter framework. When your app creates and displays a scene, the UI thread creates a layer tree, a lightweight object containing device-agnostic painting commands, and sends the layer tree to the GPU thread to be rendered on the device. Do not block this thread.
The GPU thread executes graphics code from the Flutter Engine. This thread takes the layer tree and displays it by talking to the GPU (graphic processing unit). You cannot directly access the GPU thread or its data, but if this thread is slow, it’s a result of something you’ve done in the Dart code. Skia, the graphics library, runs on this thread, which is sometimes called the rasterizer thread.
Sometimes a scene results in a layer tree that is easy to construct, but expensive to render on the GPU thread. In this case, you’ll need to figure out what your code is doing that is causing rendering code to be slow. Specific kinds of workloads are more difficult for the GPU. They may involve unnecessary calls to saveLayer, intersecting opacities with multiple objects, and clips or shadows in specific situations.
More information on profiling the GPU thread can be found at flutter.dev.
The frame rendering chart shows UI and GPU jank in shades of red. We consider a portion of the frame to be janky when it takes more than 8 ms to complete.
To achieve a frame rendering rate of 60 FPS (frames per second), each frame must render in ~16 ms or less. Since there are two portions of work for each frame (UI and GPU), each portion should complete in 8 ms or less. When this target is missed, you may experience UI jank or dropped frames.
See Flutter performance profiling for more detailed information on how to analyze your app's performance.
The flame chart shows the event trace for a single frame. The top-most event spawns the event below it, and so on and so forth. The UI and GPU events are separate event flows, but they share a common timeline (displayed at the top of the flame chart). This timeline is strictly for the given frame. It does not reflect the clock shared by all frames.
The flame chart supports zooming and panning. Scroll up and down to zoom in and out, respectively. To pan around, you can either click and drag the chart or scroll horizontally. You can also click an event to view more details in the details section below the chart.
This section shows details for a specific event. Currently, only the event name and duration are displayed. This feature is actively being worked on. We are planning to display CPU sampling data here in the future.