Flutter ThreeForge: Fix Texture Creation Fails After Mesh Add

by RICHARD 62 views
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Hey guys,

If you're diving into the world of 3D graphics with Flutter and ThreeForge, you might run into some snags when it comes to creating and initializing textures. This article breaks down a common issue encountered while trying to replace the default scene texture after modifying it with built-in meshes. We'll explore the problem, the error messages, and potential solutions to get your textures working smoothly. So, let's dive in and figure out how to keep those textures fresh and your scene looking sharp!

Understanding the Issue: Texture Initialization Fails

So, you're probably here because you're wrestling with a texture creation problem in your Flutter ThreeForge project. Specifically, this issue arises when you're trying to create a new texture to replace the existing one after you've tweaked the scene by adding meshes like spheres and toruses. Initially, the texture works perfectly fine, and you see your scene as expected. But, once you introduce those new meshes and then attempt to create a new texture, things go south. The application throws a ConcurrentModificationError, and the scene starts flickering like a disco ball gone haywire. Sounds familiar? Let's dig deeper.

Initial Setup and Expected Behavior

When you first run your Flutter application, everything seems to be in order. The console logs confirm that the EGL version and OpenGL ES are initialized correctly. A new texture is created, and your default scene renders without any hiccups. You add a sphere and a torus to the mix, and still, the scene behaves as expected. This initial success makes the subsequent failure all the more perplexing.

The ConcurrentModificationError

The real headache begins when you try to create a new texture after adding the meshes. This action triggers a ConcurrentModificationError, which is a classic sign of trying to modify a list while it's being iterated over. The error message points to a specific line in your code, typically within your UI page state (_UIPageState) or screen navigator. The stack trace gives you a detailed path of the error, leading back to a gesture recognizer, usually a tap event. This means the error is likely happening when you're tapping a button or some other UI element that triggers the texture creation.

══╡ EXCEPTION CAUGHT BY GESTURE ╞═══════════════════════════════════════════════════════════════════
The following ConcurrentModificationError was thrown while handling a gesture:
Concurrent modification during iteration: Instance(length:0) of '_GrowableList'.
...

This error is super annoying because it means that somewhere in your code, you're trying to change a list (like a list of callbacks or scene objects) at the same time that another part of your code is looping through it. It's like trying to change a tire while the car is still moving – not gonna work!

The Flickering Scene

Accompanying the ConcurrentModificationError is the disconcerting flickering of the scene. This visual glitch is a symptom of the underlying issue: the texture is not being updated correctly, and the rendering process is getting stuck in a loop. The constant flickering makes it clear that something is fundamentally wrong with how the texture is being handled after the meshes are added.

Deep Dive into the Technical Details

Okay, so we know the what and the when. Now, let's get into the why. To really nail this, we need to break down the error logs and trace the execution flow. When you see that ConcurrentModificationError, your brain should immediately think: list modification during iteration. This usually happens when you have a loop going through a list, and inside that loop, you're adding or removing items from the same list.

Analyzing the Stack Trace

The stack trace is your best friend here. It's like a detective's notepad, showing you exactly where the crime happened. In this case, the stack trace points to a few key areas:

  1. ListIterator.moveNext: This tells you the error is happening inside an iterator, which is what Dart uses to loop through lists.
  2. _UIPageState.callBacks.<anonymous closure>: This suggests the problem is within a callback function in your UI page state. Callbacks are often used for handling events, like button presses.
  3. State.setState: This is a big clue! setState is how Flutter rebuilds the UI. If you're modifying a list inside a setState call, you're likely to run into this error.
  4. ScreenNavigator.navigator.<anonymous closure> and _OverlayClassState.navSubButtons.<anonymous closure>: These indicate the issue might be related to navigation or UI elements that trigger the texture creation.
  5. Gesture Recognizers: The trace also mentions gesture recognizers (like TapGestureRecognizer), which means the error is triggered by user interaction, such as tapping a button.

EGL and OpenGL ES Logs

The logs also show some interesting messages:

INFO: EGL ERROR: eglGetConfigAttrib: EGL_ANGLE_iosurface_client_buffer is not enabled.
INFO: GL error: HIGH: Enum is not currently supported.
INFO: GL error: HIGH: Enum is not currently supported.

These messages, while not directly causing the ConcurrentModificationError, hint at potential issues with the graphics context or OpenGL configuration. The EGL_ANGLE_iosurface_client_buffer error might be related to how textures are being shared between different parts of the rendering pipeline. The