Flush Visualizer


Building smooth and visually appealing UI applications requires a keen focus on performance. To achieve efficient UI rendering, minimizing unnecessary work that consumes valuable CPU time is essential.

For example, assuming the application targets 60 FPS to perform a transition between two screens, that means the application has 1/60s ~= 16ms in total to execute the rendering and the flush (see Rendering Pipeline).

The Flush Visualizer is a tool designed to investigate potential performance bottlenecks in UI applications running on the Simulator. The Flush Visualizer provides the following information:

  • A screenshot of what was shown on the screen after a flush.
  • The list of drawing operations that were performed before this flush (and after the previous one).
  • The total area covered by the sum of the area drawn by the drawing operations as a percentage. A value of 100% indicates that the area drawn is equivalent to the surface of the entire display. A value of 200% indicates the area drawn is equivalent to twice the surface of the entire display.

A perfect application has 100% of its display area drawn. (It can even be less than 100% if only a subset of the display has changed.) A total area drawn between 100% to 200% is the norm in practice because widgets often overlap. However, if the total area drawn is bigger than 200%, that means that the total surface of the display was drawn more than twice. Probably meaning that a lot of drawings are done above others. Identifying this drawing (and the ones below) can help reducing the number of drawings done (or their surface).

As always, when conducting a performance study, measure. Use SystemView to identify the bottlenecks in your application on the embedded target. A total area drawn over 200% is inefficient, but your application may have bigger bottlenecks. Confirm it by measuring the time spent drawing vs. the time spent elsewhere between flushes.


Set the option ej.fp.display.flushVisualizer to true to enable the flush vizualizer.

This option is available for the Display widget in frontpanel widget module version 4.+ for UI Pack 14.0.0 or later.


  1. Run the application in the Simulator.
  2. Open the file MicroUIFlushVisualizer/MicroUIFlushVisualizer.html that was generated in the application output folder.


Please refer to the javadoc of the FlushVisualizer class alongside the Display widget.


Here are examples of the Flush Visualizer in action:

Simple GFX Demo Wearable
../../../_images/small-demo-ui-flush-visualizer-simpleGFX.png ../../../_images/small-demo-ui-flush-visualizer-demo-wearable.png