Federica Bucchieri
email: federica.bucchieri@inria.fr

Lijie Yao

Petra Isenberg
email: lijie.yao|petra.isenberg@inria.fr.

Visualisation Localisée en Mouvement dans les Jeux Vidéo pour Différents Types de Données

Visualization in Motion in Video Games for Different Types of Data Federica Bucchieri, Lijie Yao, and Petra Isenberg English Abstract-We contribute an analysis of situated visualizations in motion in video games for different types of data, with a focus on quantitative and categorical data representations. Video games convey a lot of data to players, to help them succeed in the game. These visualization frequently move across the screen due to camera changes or because the game elements themselves move. Our ultimate goal is to understand how motion factors affect visualization readability in video games and subsequently the players' performance in the game. We started our work by surveying the characteristics of how motion currently influences which kind of data representations in video games. We conducted a systematic review of 160 visualizations in motion in video games and extracted patterns and considerations regarding where, what, and how visualizations currently exhibit motion factors in video games.

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INTRODUCTION

While playing a video game players generate dynamic datasets about character movements, health, resources, and many other game elements. This data is often visualized to help players succeed and make decisions about their actions in the game. Frequently, those data visualizations are in motion on the screen due to camera changes or because the visualizations are attached to moving game elements. In order to use the data shown in these visualizations, players need to read them at a glance while they focus on the game's primary task. Our research aims to explore how contextual factors in video games affect the readability of visualizations in motion. We conducted a systematic review surveying the characteristics of visualizations in motion in video games. We collected 160 visualizations from 50 video games. Moreover, we analyzed how different types of data are represented in games. Specifically, we focused on quantitative and categorical data by analyzing two prominent examples of the information displayed in video games: character's health and the type of specific game elements.

RELATED WORK

Our work focuses on situated visualizations in motion for video games. Situated visualizations are data representations located near a data referent [START_REF] Willett | Embedded data representations[END_REF]. A data referent is a person, object, or location to which the visualized data refers. Willet et al. studied the relationship between visual representations and data referents, formalizing the difference between situated and embedded data visualizations. Their work is based on White's [START_REF] White | Interaction and presentation techniques for situated visualization[END_REF] investigation of presentation and interaction techniques. White proposed a theoretical framework for situated visualization, presenting best practices for the domain. Our research is related to situated visualization since we are considering game element visualizations displayed in close connection with the element itself. The notion of visualization in motion was firstly introduced by Yao et al. [START_REF] Yao | Situated visualization in motion[END_REF] in their design space. They explored motion relationships between viewers and visualizations. They analyzed motion factors and contextual factors that may affect the readability of the visualizations. In our previous [START_REF] Bucchieri | Situated visualization in motion for video games[END_REF] and current work, we have narrowed down Yao et al.'s research scope by focusing on static viewers and moving visualizations, in the context of video games visualizations. Our work is naturally related to previous work in video game visualization techniques. In 2008, Zammitto [START_REF] Zammitto | Visualization techniques in video games[END_REF] analyzed how video games present essential information to the players and if visualization techniques were used. Zammitto presented visual representations such as health bars, silhouettes, HUDs, and mini-maps. Bowman et al. [START_REF] Bowman | Toward visualization for games: Theory, design space, and patterns[END_REF] conducted a systematic review of existing games incorporating visualization to build a framework. They proposed a design space to classify any video game visualizations according to five categories: primary purpose, target audience, temporal usage, visual complexity, and immersion/integration. Our work relates to Peacocke et al.'s [START_REF] Peacocke | An empirical comparison of first-person shooter information displays: Huds, diegetic displays, and spatial representations[END_REF] evaluation of player's performances about different types of data represented in video games with different types of displays. The authors showed that different visual representations are suited for specific and diverse types of information. Our study differs from previous studies in that it focuses on visualizations impacted by motion factors in the context of game-specific elements.

SYSTEMATIC REVIEW OF VISUALIZATION IN MOTION IN VIDEO GAMES

Our work is based on a systematic review of visualizations in motion for video games [START_REF] Bucchieri | Situated visualization in motion for video games[END_REF]. We used a commercial ranking website called Metacritic [START_REF] Metacritic | Movie Reviews, TV reviews, game reviews, and music reviews[END_REF] to cover a diverse range of video games. We collected 160 visualizations in motion by surveying 50 video games from 17 genres. We selected the top 3 games from 2011 to 2022 sorted by the Metacritic relevance score for each genre. We categorized those 160 visualizations according to several dimensions related to situated visualization and motion factors. In our previous EuroVis poster we presented an analysis of five of those dimensions, while here we concentrate on how different types of data are represented in video games.

VISUALIZATION IN MOTION IN VIDEO

GAMES FOR DIFFERENT TYPES OF DATA

Video games produce a wide range of types of data, defined by the values they can express. 67 out of the 160 visualizations we analyzed represented quantitative data. This data concerned health points of a character, the number of resources crafted, or the distance from a location. Categorical data were the second most common category, with 64 out of 160 representatives. Categorical data concerned team identification and resource type. Furthermore, 49 out of the 160 visualizations showed spatial data of the data referent's position. Meanwhile, ordered data were the least frequent with 8 out of 160 representatives and were only present in racing games. In the next two sections we focus on the two most frequent quantitative and categorical data displays: character health and game element types.

Character's health

Out of 67 quantitative data visualizations, 24 represented the character's health. A typical way to represent health were horizontal bar charts (18/24 visualizations; see Fig. 1: Left). Only 3 out of 24 representatives were radial bar charts (see Fig. 1: Middle), and the remaining three were a pie chart, a label with numbers, and a pictorial fraction chart (see Fig. 1: Right). Health was sometimes represented with single-color horizontal bar charts that encoded data only by bar length. Some examples showed a dual encoding with the use of color, usually in gradients from green (healthy) to red (critical). As stated by Zammitto [START_REF] Zammitto | Visualization techniques in video games[END_REF], to be color-blind friendly, applying length as the unique method is already sufficient. 16/24 visualizations in our collection had an opaque background, while the remaining 8 had a transparent background. Having a transparent background also meant that these bars lacked a reference frame that could help to judge the length of the bar more precisely [START_REF] Cleveland | Graphical perception: Theory, experimentation, and application to the development of graphical methods[END_REF].

Game element types

To succeed in certain games, finding the right resource or correctly identifying enemies is important. This type of information is usually represented by categorical data. We found 26/160 visualizations that represented the type of game elements, such as interactive objects and characters. Signs were the most common visual representation, with 13/26 visualizations. Signs used shape and color encodings to distinguish different categories of game elements, such as mission targets (see Fig. 2: Left). Those encodings aimed to help players differentiate between other players, objects, and objectives [START_REF] Karlsson | Information visualisation in games: How do you know what you know?[END_REF]. Another prevalent method to identify character types is the use of color in the character's health bar charts (see Fig. 2: Middle). In fact, when categorizing the 26 visualizations found by the type of encoding used, it's possible to notice that the majority used color-only with 12 out of 26 representatives, while 8 out of 26 visualizations used both shape and color, and 5 used only shape (see Fig.

DISCUSSION AND FUTURE WORK

Our results show that quantitative and categorical data are the most recurrent types of data visualized in video games. According to our sample, the prevalent encoding used for quantitative data is length. Instead, color is mostly used for categorical data representations. Character's health (quantitative data) is predominantly represented by bar charts while, game element types (categorical data) by using signs. We are now designing an empirical study to evaluate the readability of different visual representations under motion in the context of video games.

ACKNOWLEDGEMENT

This work was partly supported by the Agence Nationale de la Recherche (ANR), grant number ANR-19-CE33-0012.

Fig. 1 .

 1 Fig. 1. Different types of character's health's visualizations. Left: Bar chart in Aliens: Fireteam Elite. Middle: Radial bar chart in The Falconeer. Right: Pictorial fraction chart in Skies of Fury DX. 4.2 Game element types

2 :

 2 Right). The last representative (1/26) displayed information by using text.

Fig. 2 .

 2 Fig. 2. Different game element's type visualizations. Left: missions' icons in Spider-Man. Middle: color coded health bar charts in League of Legends. Right: Resource's type signs in Aliens: Fireteam Elite.


Eurovis

/ S Lenti

M Krone

J Schmidt

Federica Bucchieri

Lijie Yao

Petra Isenberg

Situated Visualization in Motion for Video games

Keywords:

We contribute a systematic review of situated visualizations in motion in the context of video games. Video games produce rich dynamic datasets during gameplay that are often visualized to help players succeed in a game. Often these visualizations are moving either because they are attached to moving game elements or due to camera changes. We want to understand to what extent this motion and contextual game factors impact how players can read these visualizations. In order to ground our work, we surveyed 160 visualizations in motion and their embeddings in the game world. Here, we report on our analysis and categorization of these visualizations.

Introduction

With the prevalence of video games and the growing games market, many people are used to following moving game elements on the screen. Gameplay produces rich and changing data, some of which is shown to gamers in the form of visualizations that are also often moving. These visualizations are designed to aid players succeed in the game and make important decisions about how to act in the game. Examples include health bars, navigation aids, resource inventories, or team membership. As such, visualizations play an important role in how effective a player can be but they also pose a number of interesting design challenges. Visualizations need to be read at a glance while the player is focused on a primary task such as fulfilling a game mission. They also often need to be small, match the aesthetics of the game, or be closely embedded next to game elements. In order to survey the current practice of visualizations in motion in video games, we reviewed 50 games from 17 different genres. In these games we found 160 examples of visualizations in motion that we categorize according to different dimensions. Our future research goal is to design and embed visualizations in motion in the context of games and to explore the impact of contextual factors in video games on visualizations in motion.

Related Work

Yao et al.

[YBI20] proposed a first design space for visualization in motion that included the motion relationship between viewer and visualization. When playing video games this motion relationship involves a stationary player sitting in front of a monitor, seeing visualizations moving on the screen. Visualizations are situated in the game context and as such our work related to the research area of situated visualization. White [Whi09] studied different presentation and interaction techniques, investigating a theoretical framework and best practises for situated visualizations. More recently Willett et al. [WJD16] formalized the difference between situated and embedded visualization, analyzing the relationship among data and the referents to which the data refers. Our work focuses on embedded visualizations that have a close connection between data and referent; for example where data about a game character is displayed directly next to the character's representation. Our work is of course, also related to past work on visualization for video games. Zammitto [Zam08] was the first one to tackle the topic and analyze the principles of visualizations used in games. Her analysis focused on determining how video games provide the player with important visual information like the use of silhouettes, mini-maps, HUDs, Fog of war etc. Some theories and design spaces have been proposed, based on a systematic review of existing games that incorporate some sort of visualization. Bowman's [START_REF] Bowman | Toward visualization for games: Theory, design space, and patterns[END_REF] framework comprises five categories to classify any video games visualization: primary purpose, target audience, temporal usage, visual complexity and immersion/integration. Peacocke et al. [PTC * 18] studied players' performances with different types of displays to find the best way to represent different types of data. Their work shows that there is no universally best display type for every information. Different representations worked well for specific types of information (e.g. players performed better with information about ammo displayed with spatial displays). Our research deviates from this past work in that we concentrate on the motion of visualizations related to contextual factors of the game itself.

A Review of Visualizations in Motion in Video Games

To ground our work in existing practices of moving visualizations in video games we conducted a systematic review. To cover a diverse selection of video games we made use of a commercial ranking website called Metacritic [Met]. Metacritic assigns a unique Metascore to each video game, which is a weighted average of the scores of the world's most respected reviewers from the gaming field. Metacritic categorizes games according to 18 different game genres. For each genre we selected the top 3 games from 2011 to 2022 sorted by the Metacritic relevance score. We considered all gaming platforms such as PC, Xbox and PlayStation etc. We excluded puzzle games because they did not contain moving visualizations. Moreover, out of the first 50 wrestling games only two provided relevant visualizations. In total, we reviewed 50 games from 17 genres. For each game, one author of this poster watched game-plays on YouTube for approximately 5 to 15 minutes and video-recorded relevant parts of the videos where the game showed visualizations in motion.

Categorization of Current Video Game Visualizations

In total, we collect 160 examples of visualization in motion. We categorized these examples according to multiple dimensions related to situated visualization and motion characteristics:

Visualization Representation: describes how data was represented. Signs were the most prevalent representation (36/160), followed by bar charts (28/160), labels with numbers (21/160) and labels with texts (19/160). The remaining 56/160 visualizations included silhouettes, pictographs and more (see Figure 3: Left). Often additional dimensions were derived from a primary dimension. For example health bars often showed a single health percentage as a bar chart but also three different health states with a traffic light color scheme (healthy, medium, critical).

Movement autonomy: considers if the visualization was moving autonomously or was controlled by a player. For example, a player can induce motion of a static enemy's health bar on the screen by moving his or her camera, for example via one's character. Autonomous movement of a visualization was not prevalent in video games, only 5/160 samples moved autonomously, while 86/160 were consistently controlled in some way only by the player and 69/160 depended on autonomous movement and they player's control (see Figure 4: Right).

Discussion and Future Work

Our ultimate goal is to explore the impact of contextual factors in video games on visualizations in motion. We are currently in the first phase of this work. We surveyed visualizations in motions and analyzed them according to different dimensions. We are now looking for open-source games with the possibility to access their data in real-time. Furthermore, we plan to design our own visualizations in motion and then embed them into games. We may conduct empirical experiments to evaluate the readability of different visualizations in motion in the context of video games.

Acknowledgement

This work was partly supported by the Agence Nationale de la Recherche (ANR), grant number ANR-19-CE33-0012.

Figure 1 :

 1 Figure 1: Visualizations referring to different data referents in a racing game. Left: characters' speed bars. Middle: checkpoint indicator with text label showing distance. Right: signs for object type. Data referents: are the entities that the data refers to. Most referents are game characters (see Figure 1: Left), locations (see Figure 1: Middle), or an object in the game (see Figure 1: Right). In our sample collection, 114/160 data referents were game characters, 30/160 were locations, and 16/160 were objects (see Figure 3: Middle).

Figure 2 :

 2 Figure 2: Different embedding locations of visualizations in motion in a first person shooting game. Left: Health bar placed above the character's head. Middle: Health level expressed by color and silhouette overlapping the character. Right: Visualization integrated in the character's design (red color).

  Embedding locations: refer to the spatial relationship of the visualization and the data referent. We found three different types of embedding locations (see Figure3: Right). 121/160 examples embedded visualizations around the data referent. Visualizations were close to the referent for example above an object (see Figure 2: Left), under the feet of a character, or above a checkpoint (a location). 26/160 visualizations showed full or partial overlap with the data referent as shown for example in Figure 2: Middle. Finally, 13/160 visualizations were integrated with the data referent permanently for example in the material color of the referent, see

Figure 2 :Figure 3 :

 23 Figure2: Right. Although visualizations integrated or overlapped with the referent might look similar, integrated visualizations cannot be separated from the referent while overlays may be temporary.

Figure 4 :

 4 Figure 4: Counts for the number of examples including factors of the number of dimensions visualization and movement autonomy.

  Images credits: Screenshots came from the open source Unity FPS Microgame Template modified by the authors. Star icon by upklyak on freepik.com

© 2022 The Author(s) Eurographics Proceedings © 2022 The Eurographics Association.