Removing An Entity Consisting Of A Camera And ContrastAdaptiveSharpening In A Conditional System Causes Crash

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Introduction

In this article, we will explore a scenario where removing an entity consisting of a Camera and a ContrastAdaptiveSharpening component in a conditional system causes a crash in a Bevy application. We will delve into the code, identify the issue, and provide a solution.

Bevy Version and System Information

The Bevy version used in this example is 0.15.3. The relevant system information is as follows:

AdapterInfo { name: "Apple M2 Pro", vendor: 0, device: 0, device_type: IntegratedGpu, driver: "", driver_info: "", backend: Metal }

What Went Wrong

The application crashes after the update system is run. The crash is caused by the prepare_cas_pipelines system attempting to create an EntityCommands for an entity that has already been removed from the main world.

Additional Information

The log output produced after the crash is as follows:

bevy_core_pipeline-0.15.3/src/contrast_adaptive_sharpening/mod.rs:253:18:
Attempting to create an EntityCommands for entity 3v1#4294967299, which doesn't exist.
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
Encountered a panic in system `bevy_core_pipeline::contrast_adaptive_sharpening::prepare_cas_pipelines`!
2025-04-22T02:46:16.512081Z  WARN bevy_ecs::world::command_queue: CommandQueue has un-applied commands being dropped. Did you forget to call SystemState::apply?

Analysis

The prepare_cas_pipelines system is looping over a list of removals (RemovedComponents<CasUniform>) and performing commands.entity(entity).remove::<ViewCasPipeline>(). The entity in question has already been removed in the main world, hence the Attempting to create an EntityCommands for entity 3v1#4294967299, which doesn't exist.

Solution

The issue can be resolved by replacing commands.entity(entity) with commands.get_entity(entity). This will ensure that the EntityCommands is created for the entity only if it exists in the main world.

Code Changes

The updated code for the prepare_cas_pipelines system is as follows:

fn prepare_cas_pipelines(
    mut commands: Commands,
    removed_components: Query<RemovedComponents<CasUniform>>,
) {
    for removed in removed_components.iter() {
        if let Some(entity) = commands.get_entity(removed.entity) {
            commands.entity(entity).remove::<ViewCasPipeline>();
        }
    }
}

Conclusion

In conclusion, the issue was caused by the prepare_cas_pipelines system attempting to create an EntityCommands for an entity that had already been removed from the main world. By replacing commands.entity(entity) with commands.get_entity(entity), we can ensure that the EntityCommands is created only if the entity exists in the main world, thus resolving crash.

Best Practices

To avoid similar issues in the future, it is essential to:

  • Always check if an entity exists before attempting to create an EntityCommands for it.
  • Use commands.get_entity(entity) instead of commands.entity(entity) when working with removed entities.
  • Ensure that all systems are properly synchronized and that commands are applied correctly.

Introduction

In our previous article, we explored a scenario where removing an entity consisting of a Camera and a ContrastAdaptiveSharpening component in a conditional system causes a crash in a Bevy application. We analyzed the issue, identified the root cause, and provided a solution. In this article, we will answer some frequently asked questions related to this topic.

Q: What is the root cause of the crash?

A: The root cause of the crash is that the prepare_cas_pipelines system is attempting to create an EntityCommands for an entity that has already been removed from the main world.

Q: Why is the prepare_cas_pipelines system attempting to create an EntityCommands for a removed entity?

A: The prepare_cas_pipelines system is looping over a list of removals (RemovedComponents<CasUniform>) and performing commands.entity(entity).remove::<ViewCasPipeline>(). The entity in question has already been removed in the main world, hence the Attempting to create an EntityCommands for entity 3v1#4294967299, which doesn't exist.

Q: How can I prevent this crash from occurring?

A: To prevent this crash from occurring, you can replace commands.entity(entity) with commands.get_entity(entity). This will ensure that the EntityCommands is created for the entity only if it exists in the main world.

Q: What is the difference between commands.entity(entity) and commands.get_entity(entity)?

A: commands.entity(entity) creates an EntityCommands for the entity, regardless of whether it exists in the main world or not. commands.get_entity(entity), on the other hand, returns the entity if it exists in the main world, and None otherwise.

Q: Can I use commands.entity(entity) in all cases?

A: No, you should not use commands.entity(entity) in all cases. If the entity has already been removed from the main world, using commands.entity(entity) will cause a crash. Instead, use commands.get_entity(entity) to ensure that the EntityCommands is created only if the entity exists in the main world.

Q: What are some best practices to avoid similar issues in the future?

A: To avoid similar issues in the future, it is essential to:

  • Always check if an entity exists before attempting to create an EntityCommands for it.
  • Use commands.get_entity(entity) instead of commands.entity(entity) when working with removed entities.
  • Ensure that all systems are properly synchronized and that commands are applied correctly.

Conclusion

In conclusion, the crash was caused by the prepare_cas_pipelines system attempting to create an EntityCommands for a removed entity. By replacing commands.entity(entity) with commands.get_entity(entity), we can ensure that the EntityCommands is created only if the entity exists in the main world, thus resolving the crash. By following best practices, you write more robust and reliable code for your Bevy applications.

Additional Resources

For more information on Bevy and its ecosystem, please refer to the following resources: