SDL3 Clipboard support in Emscripten

[bitloop-dev]

Here is a fairly minimal example (SDL3 + imgui). Clipboard works fine in native builds, but not Emscripten.

https://github.com/willmh93/SDL3_emscripten_imgui

git clone --recursive https://github.com/willmh93/SDL3_emscripten_imgui.git
cd SDL3_emscripten_imgui
emcmake cmake -B build -G Ninja
cmake --build build
emrun build/my_app.html --port 8000

I could swear I had it working just a month ago, but now the functions SDL_SetClipboardText / SDL_GetClipboardText (which ImGui calls under the hood) do nothing for me. I can't tell if this is due to a change in my environment or an SDL bug.

Does anyone have a working example they wouldn't mind sharing? Thanks.

[icculus]

Any chance you're not running on an https connection? The clipboard API will refuse to work without one (this is a browser requirement, it's silly.)

[bitloop-dev]

Thanks for the reply.

It's still an issue with a https connection. Just to illustrate, I got the above example and stuck it on my site:

https://bitloop.dev/example_bug/

Trying to copy/paste from any input fails. I'm fairly confident SDL_SetClipboardText / SDL_GetClipboardText are being called.

[icculus]

I stand corrected: SetClipboardData and SetClipboardText aren't implemented in the Emscripten backend. :/

Let me see if this is easy to do real quick.

[icculus]

Of course the web clipboard API is asynchronous. :(

SDL_SetClipboardText() can just send the data on to the OS and not care if/when it completes, but SDL_GetClipboardText() is a different problem entirely.

I wonder how expensive it would be to just request the clipboard data once per frame and just hand the latest to the app on request. Pretty gross, though. There doesn't appear to be an event to tell us when the clipboard has new data, so we'd have to poll for it with SDL's existing API.

[bitloop-dev]

I can't offer much insight into SDL's internal implementation, but for copying/pasting plain-text, my above example is now working.

bitloop-dev/SDL3_emscripten_imgui@189c1f1

With help from emscripten-browser-support and pthom/hello_imgui#3 (comment)

[icculus]

The copy event is fired when you use the standard browser controls (like highlighting text and pressing ctrl-c, or right-click+"Copy"), but it won't fire events when the clipboard is updated in another process (or even a different browser tab), so it won't do what we need (someone copies text from a external document and tries to paste it into an SDL app).

[KonnorRogers]

@icculus I stumbled on this yesterday, and just today a new feature was added to Chrome / Edge 140 to add a clipboardchange event which seems like an elegant way to solve this problem.

https://developer.chrome.com/blog/clipboardchange

https://mas.to/@patrickbrosset/115254092814663328

[icculus]

Ooh!!

[icculus]

Registering for experimental Chrome features is wild:

[icculus]

I put together an example app for the clipboard API: https://examples.libsdl.org/SDL3/misc/02-clipboard/

This does not have the new Chrome extension yet.