# Extended Reality (XR) Engines for Developing Gamified Apps and Serious Games: A Scoping Review
## 4 Discussion
### RQ1. What Game Engines for XR Are Reported in the Literature? The literature reports multiple technologies for developing XR-enriched apps. Some of these technologies support XR natively, whereas others are assisted by some components. We classified these technologies for developing XR apps in two categories: proprietary engines for XR and JavaScript-based engines for XR. Proprietary engines use a native programming language to generate XR-based apps, whereas JavaScript-based engines, as the name suggests, use JavaScript to generate XR-based apps. According to our findings, the proprietary engines for developing XR-enriched gamified apps and serious games are as follows:  
* Google ARCore: Google's ARCore platform is used to create AR experiences. ARCore uses a variety of APIs to allow smartphones to sense their surroundings, understand the outside world, and interact with information. To share AR experiences, Android and iOS both have APIs available [68; 69; 70]. Google ARCode offers code samples licensed under the Apache 2.0 License and documentation licensed under the Creative Commons Attribution 4.0 License [71]. * Apple ARKit: Apple's AR Kit is a potent feature library and tool that enables users to take already written code and modify it to meet their functional needs. After using its animation tools to create a 2D sketch on any surface, the AR suite enables users to create anything in 3D. The two primary components of ARKit are the location of the camera in 3D space and the detection of horizontal planes [72; 73]. ARKit is an API with tools that are free to download but need the user to have an annual Developer Program account for store distribution [74]. \begin{table}
\begin{tabular}{c c} \hline \hline
**Related Areas** & **Studies** \\ \hline Gamification and virtual reality & [PERSON] et al. [23], [PERSON] et al. [24], [PERSON] et al. [25]. \\ \hline Gamification & [PERSON] et al. [26], [PERSON] et al. [27], [PERSON] et al. [28], [PERSON] et al. [29], [PERSON] et al. [30]. \\ \hline Extended Reality & [PERSON] et al. [31], [PERSON] et al. [32], [PERSON] et al. [33], [PERSON] et al. [34], [PERSON] et al. [35], [PERSON] et al. [36], [PERSON] et al. [37], [PERSON] et al. [38], [PERSON] et al. [39], [PERSON] et al. [40], [PERSON] et al. [41]. \\ \hline Serious games and Extended Reality & [PERSON] et al. [42], [PERSON] et al. [43], [PERSON] et al. [44], [PERSON] et al. [45], [PERSON] et al. [46], [PERSON] et al. [47], [PERSON] et al. [48], [PERSON] et al. [49], [PERSON] et al. [50], [PERSON] et al. [51], [PERSON] et al. [52], [PERSON] et al. [53], [PERSON] et al. [54], [PERSON] et al. [55], [PERSON] et al. [56], [PERSON] et al. [57], [PERSON] et al. [58], [PERSON] et al. [59], [PERSON] et al. [60]. \\ \hline Virtual reality games & [PERSON] et al. [61]. \\ \hline Virtual education & [PERSON] et al. [62]. \\ \hline Related Areas & Studies \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Related Research. * Unity 3D: This engine functions as both a full-featured professional game engine and a cross-platform game development tool. With this engine, it is possible to provide a rendering engine, entity engine, scripting engine, lightmap, scene control, and other features [64; 75]. Unity is a proprietary game engine with AR and XR tools that has a 30-day free trial and empowers development teams to develop and operate immersive games and interactive experiences with a powerful and production-proven set of tools [76]. * Vuforia: This engine is an AR software development kit released by Qualcomm. In addition to enabling developers to place virtual objects through the camera's viewfinder and adjust the object's position based on the background of the camera, it uses computer vision technology to instantly identify and capture flat images or 3D objects. The Vuforia SDK supports a variety of target configurations, unsigned images, and frame labels, as well as 2D and 3D object types [63; 77].