# Extended Reality (XR) Engines for Developing Gamified Apps and Serious Games: A Scoping Review
## 4 Discussion
### RQ3. What Serious Game Attributes Are Supported in XR Game Engines?
The Collaboration and Competition category is the category with the most game attributes, which include role-play, community collaboration, epic meaning, bonuses, contests, scoring, timers, coins, inventories, leaderboards, and communal discovery. In this category, the sense of teamwork and being part of something bigger than the individual player are all motivations to add collaborative elements to online gameplay. This category provides players with another unique reason to play online titles, as the alliances formed add a new dynamic to the gameplay. In the Javascript-based XR engines, the XR games engines with the least game attribute support are A-Frame and the Wonderline Engine, with almost half of the game attributes being supported; however, PlayCanvas supports all game attributes of collaboration and competition. On the other hand, in the proprietary XR game engines, HerrorMirror just supports bonuses, content, scoring, timers, and coins. Unreal Engine 5 and Amazon Sumerian support all of the game attributes in this category. Feedback/assessment can improve learning, help the learner make decisions about his strategy, and encourage the learner's motivation. The game attributes for this category are game hints, NPCs, game levels, gaining and losing lives, progress bars, dashboards,  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Extended Reality** & **Rules** & **Goals and Choices** & **Task/Challenges** & **Collaboration and Competition** & **Feedback/ Assessment** \\ \hline A-Frame & RL1, RL2, RL3, RL5 & GC1, GC2, GC7, GC3, GC6 & TC1, TC2, TC3, TC4, TC6, TC7, TC8, TC9 & CC3, CC4, CC6, CC7, CC8, CC9 & FA3, FA4, FA5, FA6, FA8 \\ \hline ThreeJS & RL1, RL2, RL3, RL5, RL6 & GC1, GC2, GC5, GC7, GC3, GC6 & TC1, TC2, TC3, TC4, TC5, TC6, TC5, CC6, CC7, CC8 & CA1, FA2, FA3, FA4, FA5, FA6, FA8 \\ \hline PlayCanvas & RL1, RL2, RL3, RL5, RL6 & GC1, GC2, GC5, GC7, GC3, GC6, GC4 & TC1, TC2, TC3, TC4, TC5, TC6, CC7, CC8, CC9 & CA1, FA2, FA3, CA5, CA6, CA7, CA8, CC9 & FA1, FA2, FA3, CA5, CA6, CA7, CA8 \\ \hline Babylon.js & RL1, RL2, RL3, RL5, RL6 & GC1, GC2, GC5, GC7, GC3, GC6, GC4 & TC1, TC2, TC3, TC4, TC5, TC6, CC4, CC5, CC6, CC7, CC8 & FA1, FA2, FA3, FA4, FA5, FA6, FA8 \\ \hline React XR & RL1, RL2, RL3, RL5, RL6 & GC2, GC7, GC3, GC6 & TC2, TC3, TC4, TC5, CC6, CC7, CC8 & CA1, CA1, CA1, CA1, CA1, CA1, CA1, CA  
progress trees, and lives/virtual currencies to be used for buying game items from an online inventory. In this category, Three.JS, PlayCanvas, and Babylon.js offer the most support for the game attributes in the Feedback/assessment category. In the proprietary XR game engines, Unity 3D, and Amazon Sumerian support all game attributes for this category, and Apple ARKit just supports game hints, NPCs, Dashboards, and progress trees. Based on the support presented by each game engine, we can establish the following conclusions: \"Rules\" and \"Task/challenges\" are the most common game category classification, and the categories \"Goals and Choices\", \"Collaboration and Competition\", and \"Feedback/assessment\" have fewer game attribute supports in the XR engines. Regarding proprietary XR engines, Unity 3D, Vuforia, Unreal Engine 5, and Amazon Sumerian have the most game attribute support. Google AR Core, Apple ARKit, and Verge3D offer fewer game attributes. Concerning the game attributes, the support of the JavaScript-based XR engines is very similar because they use JavaScript as the programming language. In some cases, it is necessary to change the game's attribute configurations, like height or width, in the XR engines.