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Show HN: I reverse engineered macOS to allow custom Lock Screen wallpapers

(cindori.com)
79 points cindori | 2 comments | 15 Sep 25 08:28 UTC | HN request time: 0.022s | source

Hi HN, I'm Oskar, a solo indie Mac developer from Sweden. For those in the Mac community, you might know me from my other apps like Sensei and Trim Enabler.

For years, I've been frustrated by the lack of customisation of macOS. In particular the Lock Screen which supports animated wallpapers, but only ones provided by Apple. There's never been a way to add your own personal videos.

I decided to figure out how to solve this, and the result is Backdrop 2.0. Backdrop is my Live Wallpaper app for Mac, it can play video wallpapers on your desktop. And now it can play on your Lock Screen too.

The core technical challenge, as you can imagine, came from trying to do something that Apple otherwise does not allow. However, through extensive reverse engineering of the macOS wallpaper system, I figured out a way to provide Backdrop wallpapers to the system in a way that allows them to play on the lock screen, and even appear in a custom section in System Settings.

I'm here all day to answer any questions—especially about the reverse engineering process, the challenges of integrating with macOS, or the experience of being an indie Mac developer.

Would love to hear your thoughts and feedback.

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doix ◴[15 Sep 25 14:48 UTC] No.45250364[source]▶
What's reverse engineering like on a Mac? Have you ever written about it? I had a lot of experience reverse engineering things on windows (win32 + x86, before 64bit was a thing) using OllyDbg and patching binaries and/or (ab)using dlls. If I had to use windows again and wanted to customize something, I'd probably use windhawk nowadays [0].

On Linux, I can just compile software myself if I need to make changes. But usually most software is configurable enough that I don't need too.

On OSX, I feel like I'm helpless. I've found very little people writing about their experiences, the tools they use, their workflows, the reverse engineered data structures etc. Can you share how you approached this?

The fact that title bars on OSX aren't a fixed size drives me crazy every single day. I looked into it briefly and realized somehow everything I know about other platforms is basically useless.

[0] https://windhawk.net/

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cosmic_cheese ◴[15 Sep 25 14:57 UTC] No.45250466[source]▶
> The fact that title bars on OSX aren't a fixed size drives me crazy every single day.

Are you talking about standalone titlebars or are you including merged/unified titlebars+toolbars? Plain titlebars have a single height and merged unified toolbars have a little bit of variance but not a lot.

Any significant variance beyond those is due to third party developers hiding the standard window chrome and drawing their own. You could probably tweak NSWindow instances to bring back the standard chrome, but it’s going to look strange since it’ll show in addition to the custom chrome.

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doix ◴[15 Sep 25 15:08 UTC] No.45250586[source]▶
I am so uneducated that I cannot even answer your question properly. But for example, the default terminal in OSX has a really nice thin bar. VSCode/Cursor have a _slightly_ thicker one. Google Chrome and Firefox are huge. The red/yellow/green buttons also don't have a consistent position between those applications.

Do you happen to know which are custom chrome and which are "unified"? It didn't occur to me that other programs could be drawing their own chrome, since they look _mostly_ native(at least to me). On windows, if something was using custom stuff it would just look completely different (i.e winamp).

I guess part of the problem is that I've never done native OSX development, so I don't know what the APIs or native toolkits are like.

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1. cosmic_cheese ◴[15 Sep 25 15:16 UTC] No.45250670[source]▶
Safari is one example of a native AppKit “unified” titlebar+toolbar, as is the Finder.

And yep, all those listed (VS Code/Cursor, Chrome, and Firefox) are examples of fully custom third party window chrome, which is why they’re so variable. A lot of cross-platform software does this. It’s worth noting that Firefox at least lets you toggle on the standard titlebar — right click the toolbar, click “Customize Toolbar…”, and toggle the “Title Bar” checkbox in the bottom left corner.

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2. doix ◴[15 Sep 25 16:21 UTC] No.45251577[source]▶
Heh, so really I just need to go with the Linux approach and recompile everything with "fixed" titlebars.

For some reason it didn't occur to me that it's non native since they do such a good job at matching the native stuff.

On a side note, I'm glad I don't use finder or safari, because those titlebars are even larger than Chrome and Firefox! Absolute insanity.