Add ViewportCommand::RequestCut, RequestCopy and RequestPaste to trigger clipboard actions

[bu5hm4nn]

Motivation

We want to offer our users a context menu with Cut, Copy and Paste actions. Paste is not possible out of the box.

Changes

This PR adds ViewportCommand::RequestCut, ViewportCommand::RequestCopy and ViewportCommand::RequestPaste. They are routed and handled after the example of ViewportCommand::Screenshot and result in the same code being executed as when the user uses CTRL+V style keyboard commands.

Reasoning

In our last release we used an instance of egui_winit::clipboard::Clipboard in order to get the Paste functionality.

However Linux users on Wayland complained about broken clipboard interaction (mikedilger/gossip#617). After a while of digging I could not find the issue although I have found references to problems with multiple clipboards per handle before (https://gitlab.gnome.org/GNOME/mutter/-/issues/1250) but I compared mutter with weston and the problem occured on both.

So to solve this I set out to extend egui to access the clipboard instance already present in egui_winit. Since there was no trivial way to reach the instance of egui_winit::State I felt the best approach was to follow the logic of the new ViewportCommand::Screenshot.

Variations

It could make sense to make the introduced enum ActionRequested a part of crates/egui/src/viewport.rs and to then wrap them into one single ViewportCommand::ActionRequest(ActionRequested).

Example

let mut text = String::new();
let response = ui.text_edit_singleline(&mut text);
if ui.button("Paste").clicked() {
    response.request_focus();
    ui.ctx().send_viewport_cmd(ViewportCommand::RequestPaste);
}

[emilk]

These needs better docstrings, because I don't get it. Are these effectively injecting events in the next frame?

[bu5hm4nn]

They are doing the equivalent of pressing CTRL + C, CTRL + X and CTRL + V (or the CMD equivalent on macOS). The reason we had to introduce this is because adding a second clipboard instance broke clipboard interaction for Wayland users. So in order to offer users a context menu with these actions, we needed a way to trigger them. Since we cannot programmatically emit keypresses currently, this seemed like a viable solution.

So maybe the docstring could say Trigger a CMD + X cut or something like that

[emilk]

I see.

Perhaps "Reads text from the system clipboard and pastes it in the next frame"

[emilk]

This should be implemented in the web backend too!

[emilk]

I see.

Perhaps "Reads text from the system clipboard and pastes it in the next frame"

[bu5hm4nn]

This should be implemented in the web backend too!

I have never used egui for web and I can't find uses of ViewportCommand outside of winit, I'm afraid I can't help with that.

[emilk]

The relevant code is here:

egui/crates/eframe/src/web/app_runner.rs

Lines 203 to 210 in ab6c3f9

	for viewport_output in viewport_output.values() {
	for command in &viewport_output.commands {
	// TODO(emilk): handle some of the commands
	log::warn!(
	"Unhandled egui viewport command: {command:?} - not implemented in web backend"
	);
	}
	}

and you can test with the instruction in https://github.com/emilk/egui/blob/master/CONTRIBUTING.md#testing-the-web-viewer

Implementing RequestPaste will be a bit of work though, as it requires an async request (a mirror to set_clipboard_text in crates/eframe/src/web/mod.rs

[bu5hm4nn]

I took a look, but I am sorry, I do not have time to get into that code. Currently web does not handle any of the ViewportCommand's so I personally don't see any hurt in it currently not supporting them.

[emilk]

I took a look, but I am sorry, I do not have time to get into that code. Currently web does not handle any of the ViewportCommand's so I personally don't see any hurt in it currently not supporting them.

Fair point

[emilk]

Looks good, but needs a merge with master

[bu5hm4nn]

@emilk Not sure if you get notified when checks pass.