# 3D Visualization in Digital Medicine Using XR Technology
## 1 Introduction
### Graphics Engines  
Functions provided by the graphics engine may include 2D or 3D graphics rendering, simulation of physical forces, collision detection, sound handling, program code and library management, running animations or network management. Currently, on the market, the 3 most used graphics engines are Unreal Engine, Unity and Godot.  
* Unreal Engine: One of the main advantages of the Unreal Engine graphics engine is its high graphics quality. The graphics engine has a number of functionalities integrated into it that allow to the user to develop high quality software. Examples of such functionalities include physics simulations and lighting. For the purposes of this article, a big advantage of the Unreal Engine graphics engine is that it fully supports development for XR platforms. The main coding language of the Unreal Engine is C++, but it also supports blueprint visual scripting, which allows less experienced programmers to work with the graphics engine. One of the weaknesses of the graphics engine is its complex interface, which can result a steep learning curve for new users. Another weakness is the system requirements of the graphics engine if all functionality is to be exploited.
* Unity: One of the greatest advantages of the Unity graphics engine is its cross-platform nature, which allows the software to be exported to more than 25 platforms, including the web, XR platforms and desktop. The user interface of the Unity graphics engine is easy to use and intuitive. This, together with the fact that the graphics engine's code language is C#, results in a less steep learning curve than was the case with the Unreal Engine. One of the drawbacks of the Unity graphics engine is that it lags behind, for example, the previously mentioned Unreal Engine in terms of graphics quality.
* Godot: Godot is an open source graphics engine that allows users to tailor its operation to their needs. The Godot engine (like the Unreal Engine and Unity) supports the development of 2D and 3D software. A big advantage of the engine is that it supports several programming languages, such as C#, C++, or its own high level programming script language. Thanks to its open source code, the Godot graphics engine is completely free and has great support for third-party developers. The user interface of the graphics engine is clean and easy to use. The Godot graphics engine (similar to the previous two graphics engines) supports software development for XR devices. As for the disadvantages of the engine, the quality of the graphics display is not as good as the two previously mentioned graphics engines.  
During our research, we chose the Godot graphics engine for the following reasons: source code-level customization, completely free, support for many programming languages, support for XR devices.  
In the use of graphics engines, two major trends can be distinguished nowadays. It can be said that the majority of graphic engines offer the user some high-level programming language (Java, C#, Python). According to the second trend, the graphics engines used today strive to ensure the so-called cross-platform export for developers. This solution greatly facilitates the work of developers, as they can publish their software on different platforms by keeping the same codebase [22].