Rainpane

A while ago I was browsing /r/MacOS and found an interesting app, Weatherling (https://www.reddit.com/r/MacOS/comments/1wqty02/weatherling_make_it_rain_on_your_desktop_windows/). I really like rainy weather (more than sunny one!), and this app was exactly my taste. It makes it rain on your Mac screen and desktop. It even simulates water pooling on your windows and running down their sides. It's a nice hobby app for a couple of dollars, and if you like the idea, I'd recommend supporting the original developer too. I wanted to tune a few things to my own taste, though. I kept hearing that Claude Opus 5.5 is really good, so I wanted to see what would happen if I built my own version. This is the result. It's called Rainpane. GitHub: https://github.com/tansan7271/rainpane --- What it does - Rain falls behind your windows. Water pools on the top edges, runs down the sides, and drips from the bottom corners. - If you move a window fast, the water stays in the air for a moment, falls, and splashes when it lands. - When you close, minimize, or hide a window, its water slides down the screen as a sheet. - Clicking makes a water drop. On macOS 26 or later the drop uses Liquid Glass. --- How Claude helped I described what I wanted, mostly with notes on how it felt, and Claude Code wrote all of it. It uses Metal shaders for the water and CGWindowList to know where the windows are. It runs smoothly on my M1 Pro, and more importantly, I could add the extra features I wanted. Claude couldn't see my screen, so it added a snapshot mode to the app. The app renders frames to image files, and Claude checked those itself before asking me to look. When something misfired and the cause wasn't clear, like when minimizing a window, it added temporary logs, asked me to repeat the action, and found the cause from the logs. Some parts came out much better than I expected, even without detailed instructions from me. For example, the water flying off and falling when you move a window, and the shine on the sheet of water when a window closes. I'm a Liquid Glass fan, so I wanted to use it somewhere. I decided to add a blob that pops when you click. macOS 27 had only been out for a short time, but Opus 5.5 read the SDK's interface files directly and wrote a small test program to inspect the glass layer's internal values. Then it fitted the effect to what I wanted. Side note: Apple doesn't limit Liquid Glass to rectangles. You can give it any shape, so the drop squashes and stretches naturally as you drag it. --- Limitations I built it only for my own setup and taste. It isn't polished like a released app, and it comes with the usual risks of full vibe coding. - It uses private macOS APIs, so a macOS update can break parts of it. - It uses about 17% CPU while it rains, on my M1 Pro with two 4K displays. - I have only tested it on my own Mac (macOS 27). - There is no prebuilt download. You can build it from source with Xcode or the Command Line Tools. --- Still, it was a more fun project than I expected. It isn't practical at all, and you'll probably get tired of it in about three minutes. But I had a good time making it. But that fun part turned out to be about 10% of the work. The other 90% is polishing it so other people can actually use it. I started on that 90% and gave up. It gave me a lot more respect for developers who finish that part and ship apps. If you're curious about what I tried, the code is on GitHub (https://github.com/tansan7271/rainpane). The design choices I asked for and the reasons behind them are in ARCHITECTURE.md. It's in Korean, because that's the language I worked in with Claude. English isn't my first language, so Claude also helped me translate this post. Sorry for any awkward phrasing! Edit: Just got Windows ARM version working!