Fix: Animation Debugger Crash With No Animation Selected

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Bug Report: Discussion category

Issue Checklist

  • [x] I have read the Contributing Guide
  • [x] I have checked the Issues/Discussions pages to see if my issue has already been reported
  • [x] I have properly titled my issue
  • [x] I did not have any mods installed when I encountered this issue

Platform

Windows (Downloadable Build)

Browser

None

Mobile Device Model

No response

Mobile OS Version

No response

Version

0.7.5 (Latest)

Description (include any images, videos, errors, or crash logs)

Hey guys, let's dive into a fix for a pesky crash that some of you might have encountered while using the Animation Debugger in the Funkin' game engine. This article breaks down the issue, explains the fix, and guides you through reproducing the bug and testing the solution. Whether you're a seasoned developer or just starting out, understanding and resolving these types of issues is crucial for creating a stable and enjoyable gaming experience. Let’s get started!

Summary

This pull request (PR) addresses a critical Null Object Reference crash that occurs in DebugBoundingState.hx. Specifically, this crash rears its ugly head when you try to drag a character in the Animation Debugger without first selecting an animation from the dropdown menu. For those unfamiliar, a Null Object Reference simply means the code is trying to use something that doesn't exist, leading to an abrupt and frustrating halt.

Understanding the Bug

When you're tweaking offsets in the Animation Debugger (within DebugBoundingState), the function mouseOffsetMovement() is responsible for saving these new offsets to the currently selected animation. It attempts to do this using the following line of code:

swagChar.animationOffsets.set(offsetAnimationDropdown.value.id, swagChar.animOffsets);

Here's where the problem lies: if offsetAnimationDropdown.value is null—which can happen if the dropdown is empty or if the user deselects any chosen animation—accessing .id will result in a Null Object Reference. This, unfortunately, crashes the game immediately. Imagine trying to open a door that doesn't exist; the game simply doesn't know how to proceed, and it throws an error.

The core of the issue stems from the fact that the code assumes there will always be a valid animation selected when attempting to save offset changes. This assumption fails when no animation is selected, leaving the system in a state where it can't properly reference the animation's ID. The consequence is a Null Object Reference, which is a common but potentially disruptive error in software development. To prevent this, a check must be implemented to ensure that the selected animation is valid before attempting to access its properties. This ensures that the game can handle situations where no animation is selected without crashing, providing a more stable and user-friendly experience.

The Solution: A Null Check

To tackle this, I've implemented a null check to ensure that offsetAnimationDropdown.value is not null before the code tries to set the animation offsets. This fix is applied directly within the DebugBoundingState.hx file. This ensures that the game gracefully handles scenarios where no animation is selected, preventing the annoying crash and keeping the debugging process smooth and uninterrupted.

File: funkin/ui/debug/anim/DebugBoundingState.hx

Before:

swagChar.animationOffsets.set(offsetAnimationDropdown.value.id, swagChar.animOffsets);

After:

if (offsetAnimationDropdown.value != null) {
 swagChar.animationOffsets.set(offsetAnimationDropdown.value.id, swagChar.animOffsets);
}

This small but mighty change ensures that the game checks whether an animation is actually selected before attempting to save any offset modifications. If no animation is selected, the code simply skips the save operation, preventing the Null Object Reference and the resulting crash. This approach keeps the game stable and allows developers to continue their work without interruption.

Expected Behavior

  • Before: The game would crash due to a Null Object Reference.
  • After: The character moves visually as you drag it, but the offsets are not saved to any specific animation ID until you select one. No crash occurs!

The expected outcome of this fix is to provide a seamless and error-free experience when using the Animation Debugger. By implementing the null check, the game is now capable of handling situations where no animation is selected without abruptly crashing. This enhancement allows developers to freely adjust and experiment with character offsets, even when starting from a blank slate or when deselecting animations. The character will still respond visually to dragging, offering immediate feedback, but the changes won't be permanently saved until an animation ID is specified. This leads to a more robust and user-friendly debugging process, enabling developers to focus on refining animations without the constant fear of encountering a crash.

Type of Change

  • [x] Bug fix (non-breaking change which fixes an issue)
  • [ ] New feature (non-breaking change which adds functionality)
  • [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Steps to Reproduce

How to Test

Testing the fix is straightforward. Here’s how you can ensure the bug is resolved and the Animation Debugger works smoothly:

  1. Open the Animation Debugger in the game. You can typically find this option in the debug or developer menu of the game. If you're not sure how to access it, consult the game's documentation or developer resources.
  2. Load a character that might result in an empty animation list. Alternatively, you can manually ensure that no animation is selected in the dropdown menu. The goal is to create a scenario where the animation dropdown has no active selection.
  3. Attempt to drag the character sprite using the mouse. Click on the character and drag it around the screen. This action triggers the offset adjustment code, which previously caused the crash.

If the fix is working correctly, you should be able to drag the character around without the game crashing. The character’s position should update visually, but since no animation is selected, these changes won’t be saved to any specific animation. To verify that the offsets are indeed not being saved, you can switch to a different animation and then switch back. The character should revert to its original position for that animation. This confirms that the null check is effectively preventing the game from trying to save changes to a non-existent animation ID, thereby resolving the Null Object Reference issue and stabilizing the Animation Debugger.

Benefits of the Fix

Implementing this fix offers several notable benefits that significantly enhance the development and debugging experience:

  • Improved Stability: By preventing the Null Object Reference crash, the fix ensures that the Animation Debugger remains stable, allowing developers to work without the constant fear of unexpected interruptions. This stability is crucial for maintaining a productive workflow and reduces frustration.
  • Enhanced User Experience: The fix provides a smoother and more user-friendly experience. Developers can freely experiment with character offsets and animations without encountering disruptive crashes, making the debugging process more efficient and enjoyable.
  • Greater Flexibility: With the null check in place, developers gain the flexibility to start adjusting animations from a blank slate. They can load a character and immediately begin tweaking offsets, even if no specific animation is initially selected. This flexibility streamlines the workflow and encourages experimentation.
  • Reduced Development Time: By eliminating crashes and improving stability, the fix ultimately reduces the time spent on debugging and troubleshooting. Developers can focus more on refining animations and less on resolving technical issues, leading to faster development cycles.
  • Better Code Quality: The fix demonstrates good coding practices by implementing a null check, which is a fundamental technique for preventing common errors. This attention to detail improves the overall quality and robustness of the codebase.

In conclusion, this fix addresses a critical issue in the Animation Debugger, resulting in a more reliable, efficient, and enjoyable development process. By implementing the null check, the game becomes more resilient, providing a better experience for developers and contributing to the overall quality of the project.