Using CustomPaint lets you draw graphics directly on the screen. This can be very fast if done right because it avoids many widget rebuilds. However, complex or frequent repaints can lower frame rates below 60fps, causing janky animations. Also, heavy painting uses more CPU and battery.
To keep your app smooth at 60fps, only repaint when needed by using shouldRepaint wisely. Cache complex drawings in Picture objects or use RepaintBoundary widgets to isolate repaints. Avoid expensive operations inside the paint method. Keep your paint code simple and use efficient drawing commands.
Custom painters add minimal size to your app bundle because they are code-based drawings, not image assets. They do not significantly affect startup time. However, if you use many custom painters or complex shaders, it can increase code size slightly.
Flutter's CustomPaint works the same on iOS and Android because it uses Skia for rendering. However, performance may vary slightly due to device GPU differences. iOS devices often have ProMotion displays supporting 120fps, so optimizing for higher frame rates can improve user experience there.
Your app takes 5 seconds to load a screen with custom painting. What is likely wrong?
Answer: You might be doing heavy painting work synchronously on the main thread or repainting too often. Consider caching drawings, reducing paint complexity, or deferring expensive calculations.