## 3 Method and Case Study

Table 1: _Cont._Phase 2: Define the user's type. Two experts in software application accessibility carried out the evaluation, in this case, on the serious games. This study defined the WCAG 2.1 for users with low vision [31]. According to the WHO [32], blindness and vision impairment affect at least 2.2 billion people around the world. Of those, 1 billion have a preventable vision impairment or one that has yet to be addressed. Reduced vision can have long-lasting effects on various aspects of life, and with increasing age, older people tend to decrease their presbyopia-related visual ability [33]. Based on these definitions, accessibility experts evaluated serious games by applying WCAG 2.1 to identify accessibility barriers. The experts have experience in the evaluation of mobile applications, web accessibility, and accessibility of educational resources since 2015 and have published several articles in high impact journals related to the topic. Phase 3: Define the test scenario. In this phase, the authors define the scenarios to navigate and interact in serious games and reach the goal. The task is to (1) enter serious games, (2) review the functionality of each serious game, and (3) check if there are barriers that prevent accessibility for serious games. In this case study, an accessibility barrier for a person with low vision [34] means that the person cannot effectively move from one point to another within serious games due to visual acuity problems. Phase 4: Explore each serious game to evaluate. In the fourth phase, the user explores and becomes familiar with the interaction mechanisms of serious games. In this phase, the evaluators identify (1) the functionalities of serious gaming; (2) if the content is adjustable with the zoom and the appearance of the game; and (3) the change of behavior according to the device, the context, and the applied configuration. Figure 2 presents a screenshot of one of the evaluated games; in this example, it is a serious game used in Physics to explain the topic of the projectile launch. \begin{table}
\begin{tabular}{r l r} \hline
**ID** & **URL** & **Subject** \\ \hline
74 tri & trig-tour/1.0.22/trig-tour\_es.html & Math \\
75 und & under-pressure/1.1.18/under-pressure\_es.html & Earth science \\
76 uni & unit-rates/1.01/7/unit-rates\_es.html & Math \\
77 vec & vector-addition/1.0.0/vector-addition\_es.html & Math \\
78 vec & vector-addition-equations/1.0.0/vector-addition-equations\_es.html & Math \\
79 wav & wave-interference/2.0.2/wave-interference\_es.html & Earth science \\
80 wav & waves-intro/1.0.2/waves-intro\_es.html & Earth science \\
81 wav & wave-on-a-string/1.1.22/wave-on-a-string\_es.html & Earth science \\
82 bui & build-a-molecule/latest/build-a-molecule\_en.html & Chemistry \\ \hline \end{tabular}
\end{table} 
Table 1: Cont. Figure 2: Screenshot Projectile Motion—PHET. Phase 5: List the barriers based on WCAG. This phase is essential, in which we list the barriers related to WCAG 2.1 for the evaluation of serious games. The barriers are listed in Table 2, which contains 29 guidelines considered in the manual evaluation of each serious game. Table 2 shows the guideline, the barrier, the WCAG 2.1 principle, the success criteria, and the level. Phase 6: Evaluate with automatic tools and manually. In this phase, we evaluated the 82 serious games detailed in Table 1. We applied a combined evaluation using two automatic tools: (1) Colour Contrast Analyser (CCA), version 3.0.1 [35], a tool used to analyze some WCAG 2.1 to set the input colors of plain text. It also allows support for alpha transparency in foreground colors, includes a color blindness simulator. This tool allows a foreground and background color swatch to be taken to measure the contrast against which a report is output with WCAG 2.1.