Update file dialog example to be non-blocking.

[hydra]

This PR updates the file dialog example to be non-blocking, additionally:

• the 'Open file...' button is disabled while picking.
• the main windows is responsive while picking - you can still drag files onto it and resize it just fine.
• the picked file message is removed if the dialog is cancelled (try picking, then picking again and cancelling)
• added 'try_lock' to mutex API, with tests.

The result of a pick is recorded and kept in the state as before.

Video:
https://github.com/user-attachments/assets/29dd4cd9-b769-44f2-abe2-bd533728cdba

Related issues:

• File dialogs and drag-and-drop of files #270

Related discussions:

• Native file/directory picker #987 (comment)

• How to avoid RFD file dialogs hanging egui? #5621

• I have followed the instructions in the PR template

[hydra]

This is my first PR for egui, be gentle 😄

[hydra]

Also, I know this is just an example, but perhaps after merging this you might be interested in a PR to move the FilePicker from this PR into the main code base somewhere and expanding the API for the common use cases (files, directories, specification of path and file types).

I note that other GUI frameworks I've used have 'rfd' features and similar APIs.
Cushy - https://github.com/khonsulabs/cushy/blob/main/src/dialog.rs#L352-L464

[YgorSouza]

Also, I know this is just an example, but perhaps after merging this you might be interested in a PR to move the FilePicker from this PR into the main code base somewhere and expanding the API for the common use cases (files, directories, specification of path and file types).

I note that other GUI frameworks I've used have 'rfd' features and similar APIs. Cushy - https://github.com/khonsulabs/cushy/blob/main/src/dialog.rs#L352-L464

I think it would be hard to implement this in a way that covers all the use cases of egui. For example, on wasm you can't spawn threads, so you have to use async, and then in rfd you have to pick which async backend you're using (async-std or tokio). Then there's the game engines and such. There are a couple of file pickers implemented as egui widgets instead of using rfd, as third-party crates. They are listed in the wiki.

[hydra]

Also, I know this is just an example, but perhaps after merging this you might be interested in a PR to move the FilePicker from this PR into the main code base somewhere and expanding the API for the common use cases (files, directories, specification of path and file types).

I note that other GUI frameworks I've used have 'rfd' features and similar APIs.
Cushy - https://github.com/khonsulabs/cushy/blob/main/src/dialog.rs#L352-L464

Also, I know this is just an example, but perhaps after merging this you might be interested in a PR to move the FilePicker from this PR into the main code base somewhere and expanding the API for the common use cases (files, directories, specification of path and file types).
I note that other GUI frameworks I've used have 'rfd' features and similar APIs. Cushy - https://github.com/khonsulabs/cushy/blob/main/src/dialog.rs#L352-L464

I think it would be hard to implement this in a way that covers all the use cases of egui. For example, on wasm you can't spawn threads, so you have to use async, and then in rfd you have to pick which async backend you're using (async-std or tokio). Then there's the game engines and such. There are a couple of file pickers implemented as egui widgets instead of using rfd, as third-party crates. They are listed in the wiki.

Yes, I understand that there's various backends for async and limitations with wasm. I feel it would still be ok to provide solution for the common native desktop use-case however, along with appropriate module documentation containing links to the wiki of course. This feels like it would serve the community better rather than requiring each egui developer to implement, test and debug their own API for a common use-case no?

[landaire]

IMO this should supplement the existing blocking example, possibly as a button indicating a blocking dialog and another indicating non-blocking.

[emilk]

The blocking rfd calls need to be on the main thread: https://docs.rs/rfd/latest/rfd/#macos-non-windowed-applications-async-and-threading

To get non-blocking file dialogs, you should use the async versions instead.

In any case, I'd like to keep the original example simple. If you want to make an async version, I suggest you create a separate example for it.