RFC: Screenshot support by reading render surface and writing to file(s)

[justonia]

The project I'm working on has the need to automate screenshot collection. I wanted to socialize interest in how this might be supported in Ghostty.

This RFC PR implements screenshot support in the most straightforward way:

• Any thread calls ghostty_surface_screenshot(string path).
• The call queues a message into the render thread's mailbox and also requests a redraw.
• After the frame renders, the surface contents are read synchronously, encoded to png, and written to each path requested via ghostty_surface_screenshot.

I considered going the route of a callback-based approach:

typedef void (*ghostty_screenshot_cb)(void* userdata, const uint8_t* png_data, size_t len);

void ghostty_surface_screenshot(ghostty_surface_t surface, ghostty_screenshot_cb callback, void* userdata);

But, the file-based approach was simpler to prototype and I wanted to gauge interest in this functionality being a part of Ghostty at all before taking this further.

[bo2themax]

We should open a discussion for this first, I remember seeing a similar one

[justonia]

Was this the PR you're thinking of? #11601

[justonia]

@bo2themax Created a discussion: #12057

[00-kat]

Just so you know: opening RFC PRs is almost always the wrong thing to do in the Ghostty repository; per CONTRIBUTING.md § Pull Requests Implement an Issue:

Pull requests are NOT a place to discuss feature design. Please do not open a WIP pull request to discuss a feature. Instead, use a discussion and link to your branch.