When developing apps for Android, choosing the right rendering system can have a significant impact on performance, especially when aiming for smooth frame rates like 120 FPS. Two popular approaches are ImGui (Immediate Mode GUI) and Canvas drawing (native to Android). In this post, we’ll dive into a comparison between these two methods, helping you decide which is the best for your app.
What is ImGui?
ImGui is an immediate-mode graphical user interface library primarily used in desktop applications and games. It dynamically builds and redraws the UI every frame, making it ideal for real-time applications where constant updates and fast interaction are required. Typically, ImGui is used in conjunction with C++ and OpenGL or DirectX, but it can also be integrated with Android via JNI.
What is Canvas Drawing?
Canvas drawing is Android’s native method for rendering graphical elements on the screen. It operates in a retained mode, meaning the UI is only redrawn when needed, rather than every frame. This can make it more efficient in resource-constrained environments like mobile devices. Developers often use Canvas to build custom views, animations, and graphical elements directly within the Android framework.
ImGui vs. Canvas Drawing: A Side-by-Side Comparison
| Feature | ImGui | Canvas Drawing |
|---|---|---|
| Performance | Real-time updates, redrawn every frame. High CPU and GPU usage at 90 FPS. | Efficient for static UIs. Redraws only when needed, reducing resource usage. |
| Suitability for Mobile | Not optimized for mobile devices, built for desktop/game environments. Needs JNI integration. | Optimized for Android, works smoothly with native APIs. |
| Ease of Use | Easy for dynamic UIs but may require custom JNI bindings. Immediate mode simplifies UI logic. | Requires more code to handle state changes and custom drawing. Retained mode might be more complex for interactive UIs. |
| CPU Usage | Higher due to continuous UI rebuild every frame. | Lower, as only changes are redrawn. |
| GPU Usage | Higher, especially for complex UIs at high frame rates like 90 FPS. | More efficient GPU use, hardware-accelerated. |
| Integration | Works with C++ via JNI, which adds overhead on Android. | Native to Android, fully supported by Android Studio. |
| Use Case | Best for dynamic, real-time apps (e.g., game tools, debugging UIs). | Ideal for static or moderately interactive UIs in mobile apps. |
When to Use ImGui
ImGui is a great choice when you need to build a highly interactive and dynamic UI that changes frequently. For example, apps that require constant data updates or real-time performance tweaking (like debugging tools or in-game UIs) may benefit from ImGui’s flexibility. However, its higher resource usage means it’s not ideal for typical Android applications or devices with limited processing power.
- Best for: Dynamic, real-time applications where the UI is always changing.
- Drawback: Higher CPU/GPU load and requires JNI, making it less suitable for mobile platforms.
When to Use Canvas Drawing
Canvas is the native solution for Android, and it’s optimized for mobile devices. It’s ideal when your UI doesn’t need to be updated every frame and can be more resource-efficient by only redrawing when necessary. For most standard apps, Canvas is the better choice, especially if you’re dealing with static or moderately dynamic UIs like settings screens, menus, or dashboards.
- Best for: Standard mobile apps, static or low-interaction UIs, and custom view rendering.
- Drawback: May require more manual code to handle interactive UIs, but this can be mitigated by using Android’s built-in UI components.
Conclusion: Which One Should You Choose?
If you’re building a real-time interactive tool or app where the UI is constantly changing, ImGui might be a better choice, especially if you’re already working in C++ and can manage the additional resource consumption. However, for most Android apps, Canvas drawing is the way to go. It’s optimized for the platform, uses fewer resources, and integrates seamlessly with Android’s lifecycle and hardware acceleration.
For your Android project, the choice depends on the complexity of the UI and how often it needs to be redrawn. If you’re targeting smooth performance at higher FPS with minimal resource usage, Canvas drawing will likely serve you better, ensuring efficient use of CPU and GPU resources while keeping the app responsive and lightweight.
