Month: July 2024

Accessing the Swiss Ephemeris

The Swiss Ephemeris(SE) is the standard library for astronomical calculations in astrological software. The SE is written in Ansi C and is easy to use by programs written in C or C++. For software in other languages, a dll is available but this of course is only usable in a Windows environment.

My intention is to rewrite the core of Enigma in Go and the user interface in Flutter/Dart. This means that I need to access the SE using code in Go. Three options are available:

  • rewriting the SE in Go. This would be an enormous task.
  • using the DLL. This would restrict the usage of Enigma to a Windows environment and I want to move to a cross-platform application.
  • accessing the C-code of the SE via a FFI (Foreign Function Interface) solution. Fortunately, such a solution exists for Go. It’s called cgo.

Using cgo, I can use the original c-code in my application and call C-functions from Go. This approach does require converting Go-variables into their C counterparts and it has some limitations on constructions with pointers. And there is a performance penalty: the conversion takes time and calling a C-function from Go is much slower than calling a C-function from C.

How does this work out in practice? I can already tell you that you would not be able to see any difference for a chart-calculation. But it could be an issue if a large sequence of calculations is required, e.g. for cycles.

I wanted to be sure about this, so I built a small wrapper for the SE, using cgo. The wrapper supports two functions: initializing the SE and calculating the position of a celestial body. I used code from the existing Go wrapper by Kaveh Shahbazian (https://github.com/workshop-depot/gosweph ) but needed to make some changes. I used this wrapper in a small program that calculates the position of Sun, Moon and Mercury for 1,000,000 consecutive days. I also wrote a program with the same functionality in C#, using the standard dll from the SE. The following table shows the time these calculations took, measured in milliseconds.

Calculation forMilliseconds when using Go and cgoMilliseconds when using C# and the SE dll
Sun10,3518,935
Moon10,4028,784
Mercury11,4509,623

The results show clearly that the combination of C# and the SE dll is faster but the differences are pretty small, a bit over 15%. In both cases we are talking about roughly 100,000 calculations per second. My conclusion: there is a small performance penalty when accessing the SE with Go but it is negligible.

I performed the tests on a PC with Windows 11, an AMD Ryzen 9 processor and 32 GB internal memory.

Enigma cross-platform

Enigma is currently only compatible with Windows. For a long time, I assumed that the vast majority of astrologers used Windows. That the Windows share was declining, both due to the popularity of Apple and mobile platforms, was of course well known. But this process is moving faster than I thought. On June 25, 2024, I posted a survey in a popular Dutch Facebook group about astrology. My question: which environment was preferred for working with astrological software. 77 people responded, yielding the following score:

  • Windows (desktop/laptop): 51%
  • Apple MacOs (desktop/laptop): 10%
  • Linux (desktop/laptop): 3%
  • Apple iOs/iPadOs (smartphone/tablet): 25%
  • Android (smartphone/tablet): 11%

A survey like this is improvisational but you can glean some important conclusions from it:

  • half of the astrologers prefer Windows.
  • over a third work with Apple equipment.
  • and a third of astrologers work with Apple or Android mobile devices.

I draw the conclusion that it is insufficient to develop Enigma only for Windows. You can, of course, run Windows applications on an Apple computer via emulation software like Parallels. However, that is a stopgap solution and, moreover, it does not work on mobile devices. What you need is a cross-platform application, a program that works on desktops with Apple, Linux or Windows and also on mobile equipment with Apple or Android.

Realizing this will take a lot of time. So much time that for now I will continue to develop Enigma in the C# programming language, so only for Windows. In parallel, I am starting to convert to another environment that is cross-platform. At the latest by the time Enigma is ready for release 1.0, and the main functionality is built, I’ll make the switch. This will probably take a year or two.

Technical Choices

To move to a new way of working that supports cross-platform development, I need to make three important choices:

  • What will be the core programming language.
  • How do I approach the Swiss Ephemeris.
  • What techniques do I use to build the GUI.

Programming Language

I have looked not only at supporting cross-platform development but also at general aspects of programming languages. Almost always, I worked with object-oriented languages such as Java, Kotlin and C#. This had the advantage that I was better able to write larger and complex programs. But object orientation also has a disadvantage: you have to be very careful about over-engineering. I started looking for alternative languages and found two candidates: Rust and Go. Rust is a language that is especially suitable for critical applications and for applications that need to work in real time, like system software. I worked with Rust for a short time and found it to be a well-thought-out language. But Rust is complex and is known for its “steep learning curve”. Go is less rigorous than Rust but offers sufficient guarantees of reliable applications. Go is less suitable for time-critical applications because – unlike Rust – it works with a garbage collector. The big advantage of Go is that it is a minimal language. As a result, you can easily learn Go. Moreover, the small instruction set is pragmatic and you have a large amount of libraries you can use. Due to the lack of much syntax sugar, Go compiles very quickly and has excellent performance. The choice therefore is Go, with Rust as an alternative.

I do not consider languages like C and C++, even though they offer easier access to the Swiss Ephemeris (see next section). The chance of wrong memory allocations is very high in these languages; Rust would be a better alternative. Python is also not considered, in my opinion it is difficult to write large projects in Python, in addition Python offers much lower performance than native compiled languages.

Swiss Ephemeris

The Swiss Ephemeris (SE) is written in C. To access it from another language, there are three options:

  • a port: completely rewriting the SE in the desired language.
  • a wrapper: placing the original C code of the SE in a wrapper of the desired language.
  • JNI: Java Native Interface, a standard way to access compiled code from another environment.

Writing a full port is very much work but is possible. Thomas Mack wrote a port of the SE in Java, years ago, and it worked very well. But the SE consists of tens of thousands of lines of code, if you write a port you spend a lot of time both building and maintaining it: you also want to support future versions of the SE. A possible option but certainly not attractive.

A wrapper is easier to write, especially in Go and Rust. Wrappers in Go, that I can reuse, already exist. This seems like a useful solution.

JNI in itself is ideal but only works with languages that use the JVM: Java, Kotlin etc. Kotlin in particular is an excellent language but does carry the risk of over-engineering.

GUI

The current version of Enigma uses WPF for the GUI. WPF is complex but allows for a highly scalable GUI. Unfortunately, WPF is only suitable for Windows. An alternative like MAUI is still too immature and also does not support Linux GUI’s.

Broadly speaking, there are two alternatives:

  • an on-line application.
  • a web-based application, but packaged as a native application.
  • a cross-platform native library.

An on-line application has its problems: you would not have good capabilities for using a database and only limited capabilities for storing user preferences. Moreover, an Internet link does not give the feeling of an application: you build a relationship with the users to a lesser extent.

A Web-based native application does behave like a real application but requires the use of JavaScript; I see that as a major drawback. You can choose from platforms like Electron.js and Tauri. But Electron.js does not support mobile platforms. Tauri plans to do so in the future but is not yet that far. Tauri does require the use of Rust.

A well-known cross-platform native library is Flutter. Originally intended for mobile applications, Flutter now supports all relevant desktop variants. Flutter uses Dart, an object-oriented language. Dart is not suitable for the backend; for that you are better off using Go. Flutter and Go work very well together.

Conclusion.

  • Programming language backend: Go
  • Frontend programming language: Dart
  • GUI: Flutter
  • SE: wrapping.

I hope to regularly publish findings on the progress of this project. Enigma will remain open source, the code, including future cross-platform code, you can use in your own project, as long as your own code is also open source.