Understanding the Clickteam Fusion Runtime

Event Loop Architecture

Clickteam Fusion operates on a frame-based event engine. All conditions and actions are evaluated every frame in a top-down order. Performance and logic issues often arise from misunderstanding how events are processed, particularly in large games with hundreds of active objects.

Platform-Specific Runtime Differences

Fusion compiles your game into platform-specific runtimes (Windows, Android, iOS, HTML5). Not all behaviors are replicated identically. For instance, certain extensions available in Windows are unsupported on mobile platforms, leading to crashes or missing functionality.

Common Troubleshooting Areas

1. Recursive or Conflicting Events

Infinite event loops or conflicting triggers can cause games to hang or behave unpredictably. Use flags or qualifiers to isolate these issues:

// Use Flags to prevent re-triggering
If Flag 0 of Object is OFF
Then: Set Flag 0 ON
      Perform Action
      Set Flag 0 OFF

2. Memory Leaks and Object Spawning

Excessive creation of active objects without proper destruction leads to performance degradation or crashes on mobile:

// Cleanup created objects
If Number of Object > 200
Then: Destroy oldest instance

Monitor object counts using the built-in debugger during runtime testing.

3. Asset Loading Errors

Fusion preloads assets based on the frame structure. If assets are dynamically loaded or large in size, they can cause crashes or missing graphics, especially in HTML5 or Android builds. Consider splitting large frames or using smaller texture atlases.

4. Extension Conflicts

3rd-party extensions may behave differently on non-Windows platforms. Always verify compatibility before deploying:

  • Check extension documentation for platform support
  • Disable suspicious extensions and test core game behavior
  • Use Fusion's built-in alternatives when possible

Diagnostics and Debugging Techniques

1. Using the Built-in Debugger

Clickteam's debugger provides live updates on object instances, values, and flags. Always keep it open during runtime testing to trace irregular behavior.

2. Logging Variables and States

Fusion lacks a console, but you can create custom logging with string objects or files:

// Write debug info to a text object
Set String to: "Enemy Count: " + Str(Count("Enemy"))

3. Isolating Faulty Events

Temporarily disable groups of events to identify where the logic fails. Use "Activate/Deactivate Group" logic blocks to narrow down bugs.

Optimization Strategies for Large Projects

1. Reduce Number of Active Objects

Clickteam Fusion's runtime is optimized for small-scale object counts. Consider batching visuals or using spritesheets instead of individual actives for particles or UI.

2. Reuse Qualifiers

Use qualifiers to reduce duplicated logic across multiple object types. This improves both performance and maintainability.

3. Avoid Real-Time Loops

Loops like FastLoop can cause performance spikes if used extensively per frame. Replace with timed or event-triggered actions where possible.

Platform-Specific Deployment Fixes

1. Android Export Errors

Issues like missing permissions or incompatible extensions can prevent APK generation. Ensure:

  • Gradle and Android SDK are properly configured
  • Min SDK version matches extension requirements
  • No unsupported Windows-only extensions are used

2. HTML5 Runtime Bugs

HTML5 builds are prone to resource loading issues and timing bugs. Tips:

  • Use preloaders to avoid white screen delays
  • Limit object count and physics-based events
  • Test in multiple browsers (Chrome, Firefox) for compatibility

Best Practices for Stability

  • Modularize event logic with groups per system (e.g., input, AI, UI)
  • Use flags or alt values instead of duplicate object types
  • Always test builds on target hardware early in development
  • Regularly backup your MFA and export to MFAA (archived format)
  • Limit cross-frame object dependency; use global values instead

Conclusion

Clickteam Fusion's simplicity is a double-edged sword—it enables rapid prototyping, but without architectural rigor, large projects can become unmanageable. By applying disciplined event grouping, debugger analysis, and platform-specific profiling, developers can ensure their games remain performant and stable across all targets. The key is to treat Fusion projects with the same systematic approach as traditional codebases.

FAQs

1. Why does my game run fine on Windows but crash on Android?

It's often due to unsupported extensions or memory overuse. Check logs via Android Studio and verify each extension's compatibility.

2. How do I debug logic in deeply nested events?

Use debug strings or temporary counters to track event paths. Deactivate unrelated groups to isolate behavior.

3. What's the limit of active objects in Fusion?

While there's no hard-coded limit, performance degrades rapidly beyond 200–300 active objects. Use object recycling or spritesheets to optimize.

4. How can I test for memory leaks?

Monitor object count in the debugger. Repeated increases without drops suggest leaks. Destroy unused objects and avoid infinite creation loops.

5. Can I refactor events like code?

Yes—use groups, qualifiers, and behaviors to encapsulate logic. This helps maintainability and allows reuse across objects and frames.