Understanding Clickteam Fusion Architecture

Event-Based Logic

Clickteam Fusion operates on an event-driven model. Events are processed in a top-down loop every frame, with conditions and actions evaluated accordingly. Unlike code-based engines, this structure can make debugging large systems difficult when logic becomes highly nested or fragmented across multiple event sheets.

Runtime and Exporters

Fusion games run on a compiled runtime (Windows, HTML5, Android, iOS, etc.). Each exporter has its own set of quirks, performance limitations, and unsupported features. What works in the Windows runtime may behave differently on mobile or web exports.

Common Issues in Large Projects

Issue #1: Event Execution Order Bugs

Symptoms: Logic executes out of order, causing unexpected behavior (e.g., variables not updating in time).

Root Causes:

  • Misordered conditions and actions
  • Modifying a value and reading it in the same event frame
  • Using fast loops incorrectly inside triggered conditions
// Incorrect ordering
Set Global Value A to 1
Compare Global Value A = 1 → Action (fails due to delayed update)

Fix:

  • Break logic into separate events using flags or temporary variables
  • Use "On loop" instead of checking conditions immediately

Issue #2: Memory Leaks or Crashing on Export

Symptoms: Game crashes or slows down over time, especially on mobile platforms.

Causes:

  • Excessive use of object creation without destruction
  • Large or uncompressed assets (e.g., high-res PNGs, MP3s)
  • Leaking extensions or unhandled loops
// Example: Object pool approach
Instead of always creating bullets, recycle them by repositioning off-screen and resetting flags

Issue #3: Unexpected Behavior on HTML5 or Android

Symptoms: Features work in the Windows runtime but fail on other exporters.

Diagnosis:

  • Check compatibility of extensions (not all support non-Windows exporters)
  • Ensure all resources are explicitly included in the project
  • Avoid Windows-specific functionality like INI files unless using compatible extensions

Performance Bottlenecks

Frame Rate Drops in Complex Scenes

Causes:

  • Too many active objects on screen
  • Heavy use of always-triggered events ("Always" conditions)
  • Inefficient collision or overlap checks

Fixes:

  • Limit the use of Always; replace with meaningful triggers
  • Group logic into functions using event groups that activate/deactivate as needed
  • Use qualifiers and collision masks to reduce redundant checks

Large Frame Size Impact

Fusion processes entire frame areas regardless of the visible screen, unless optimized. This can severely degrade performance on large scrolling levels.

// Optimization tip
Set "Destroy if too far from window" for off-screen objects

Build and Deployment Troubleshooting

Android Build Errors

Symptoms: APK build fails or app crashes on startup.

Common Issues:

  • Incompatible Java/SDK version
  • Unsigned APK not accepted on newer Android versions
  • Missing permissions or manifest configuration
// Ensure Java 8 and latest Android SDK via Fusion Preferences
Set min API level to 21 or above for modern devices

HTML5 Export Crashes or Blank Screen

Causes:

  • Asset path issues (case sensitivity on Linux hosting)
  • Unsupported extensions or events
  • Browser blocking local file access

Fix:

  • Test export via local web server instead of file:// protocol
  • Use browser console to diagnose JS errors

Debugging and Diagnostics

Using the Debugger

Fusion includes a built-in debugger during runtime (F8 key). It displays object properties, memory usage, and real-time values of variables.

Best Practices:

  • Monitor object counts to avoid hidden leaks
  • Use breakpoints by isolating problematic logic in separate groups

Event Group Isolation

To debug logic, disable all but one group of events to narrow down the faulty condition.

// Toggle group state
Deactivate Group "AI"
Activate Group "Player Input"

Best Practices for Large-Scale Fusion Projects

  • Use consistent naming for objects and groups
  • Modularize logic using behaviors and event groups
  • Regularly test on all export targets during development
  • Manage assets with compression and memory limits in mind
  • Leverage object pooling instead of constant creation/destruction

Conclusion

Clickteam Fusion enables rapid development, but scaling it to professional-level projects introduces challenges that require strategic planning and optimization. Developers must go beyond the visual interface to understand the underlying execution model and memory behavior. By applying modular architecture, aggressive debugging, and exporter-specific adjustments, Fusion projects can achieve smooth performance and stable deployment across platforms.

FAQs

1. Why does my object behave differently in Android export than in Windows?

Most likely, the extension or event used is not fully supported on Android. Check the exporter documentation and replace with mobile-friendly alternatives.

2. How can I optimize Always conditions?

Replace them with specific triggers (e.g., On Animation End, Timer events) or wrap them inside deactivated groups that only activate when necessary.

3. What's the best way to manage many similar objects?

Use Qualifiers to group similar objects and apply the same logic once instead of duplicating events per object type.

4. How do I avoid crashes on HTML5 export?

Remove unsupported extensions, ensure all assets are lowercase and correctly mapped, and test in a live server environment instead of opening the HTML file directly.

5. Why does the game slow down during long play sessions?

This is often due to object or memory leaks—objects not being destroyed, or loops running unchecked. Use the debugger to monitor object counts and optimize cleanup logic.