A .NET 11 Windows theme switcher (Win32 interop & local solar math)

Humberto Schoenwald — Mon, 13 Apr 2026 09:04:58 +0000

I just built an app and I want GitHub stars. If it works for your personal use, perfect.

Now, for the developers (which is probably all of you, haha):

I built this app for fun and because auto dark-mode is genuinely a feature I miss from macOS when I'm using Windows. I made it extremely lightweight—it currently uses around 34MB active and 8MB idle.

Here is a fun fact about the development: I initially built the first version using WPF. It looked beautiful, but it was consuming around 130MB of RAM just sitting there doing nothing. I knew people were going to hate that, and I knew I could do better. I scrapped that UI layer and rewrote it using raw Win32. Even though I honestly wouldn't care if it consumed 300MB of RAM on my own machine, rewriting it to be that light became a fun optimization challenge.

Another fun fact regarding the repository quality: I manually whitelist every single Spanish word used in the LÉEME.md (Spanish README). Instead of "contaminando" my environment with standard language extensions, I maintain dedicated .txt dictionaries inside a .cspell directory. This ensures that only intentional, approved terms are permitted and prevents English typos from being masked as valid Spanish words during the CI process.

I focused on keeping it private and secure, obviously, without storing coordinates in plain text by using Windows DPAPI. (This doesn't protect your coordinates against a massive virus taking over your PC, but it keeps them properly encrypted locally).

Technical implementation facts:

Math over APIs: It calculates the solar schedule locally using the Julian day and observer coordinates instead of pinging external weather APIs. It natively handles mathematical edge cases like Polar Nights and Midnight Sun.
Native Application Lifecycle: I'm bypassing heavy frameworks. The app runs on a sealed NativeApplication class that handles single-instance locking via Mutex, manual ServiceProvider validation, and a pure native Win32 message loop via NativeInterop.RunMessageLoop().
Zero UI Frameworks: Everything is built using raw Win32 interop via LibraryImport. To make the theme transition seamless without requiring app restarts or causing screen flickers, it hooks into undocumented uxtheme.dll exports (#104 and #136).
High-Quality Tooling: I set up a strict GitHub Actions pipeline enforcing Conventional Commits via commitlint, spell-checking via cspell (using my custom local dictionaries), and automatic CalVer releases.

My purpose in uploading this: to get stars to build reputation and make money from this (using it as a portfolio), besides validating the time I invested in it haha.

If anyone finds the technical stuff useful to copy, go ahead. Here is what you can learn or reuse from the repo:

How to structure a Modular Monolith with Vertical Slices.
Implementing zero-framework native Win32 UIs in C#.
Replacing exceptions with the functional Result<T> pattern.

Bonus: I also included my entire .cursor/rules directory and AGENTS.md. These are file-scoped rules that prevent AI agents (like Cursor) from hallucinating and keep them strictly following C# 15 / .NET 11 standards.

🔗 auto-theme-solar-engine on GitHub

DEV Community: Humberto Schoenwald

A .NET 11 Windows theme switcher (Win32 interop & local solar math)

Technical implementation facts: