Background Over the last few years, the rapid advancement of technology has led to the development of many approaches to digitalization. In this respect, metaverse provides 3D persistent virtual environments that can be used to access digital content, meet virtually, and perform several professional and leisure tasks. Among the numerous technologies supporting the metaverse, immersive Virtual Reality (VR) plays a primary role and offers highly interactive social experiences. Despite growing interest in this area, there are no clear design guidelines for creating environments tailored to the metaverse. Methods This study seeks to advance research in this area by moving from state-of-the-art studies on the design of immersive virtual environments in the context of metaverse and proposing how to integrate cutting-edge technologies within this context. Specifically, the best practices were identified by i) analyzing literature studies focused on human behavior in immersive virtual environments, ii) extracting common features of existing social VR platforms, and iii) conducting interviews with experts in a specific application domain. Specifically, this study considered the creation of a new virtual environment for MetaLibrary, a VR-based social platform aimed at integrating public libraries into metaverse. Several implementation challenges and additional requirements have been identified for the development of virtual environments (VEs). These elements were considered in the selection of specific cutting-edge technologies and their integration into the development process. A user study was also conducted to investigate some design aspects (namely lighting conditions and richness of the scene layout) for which deriving clear indications from the above analysis was not possible because different alternative configurations could be chosen. Results The work reported in this paper seeks to bridge the gap between existing VR platforms and related literature in the field, on the one hand, and requirements regarding immersive virtual environments for the metaverse, on the other hand, by reporting a set of best practices which were used to build a social virtual environment that meets users' expectations and needs. Conclusions Results suggest that carefully designed virtual environments can positively affect user experience and interaction within metaverse. The insights gained from this study offer valuable cues for developing immersive virtual environments for the metaverse to deliver more effective and engaging experiences.

Technologies such as chroma-key, LED walls, motion capture (mocap), 3D visual storyboards, and simulcams are revolutionizing how films featuring visual effects are produced. Despite their popularity, these technologies have introduced new challenges for actors. An increased workload is faced when digital characters are animated via mocap, since actors are requested to use their imagination to envision what characters see and do on set. This work investigates how Mixed Reality (MR) technology can support actors during mocap sessions by presenting a collaborative MR system named CoMR-MoCap, which allows actors to rehearse scenes by overlaying digital contents onto the real set. Using a Video See-Through Head Mounted Display (VST-HMD), actors can see digital representations of performers in mocap suits and digital scene contents in real time. The system supports collaboration, enabling multiple actors to wear both mocap suits to animate digital characters and VST-HMDs to visualize the digital contents. A user study involving 24 participants compared CoMR-MoCap to the traditional method using physical props and visual cues. The results showed that CoMR-MoCap significantly improved actors’ ability to position themselves and direct their gaze, and it offered advantages in terms of usability, spatial and social presence, embodiment, and perceived effectiveness over the traditional method. • Technologies like motion capture and visual effects are revolutionizing filmmaking. • New technologies have increased actors’ workload when animating via motion capture. • Actors are required to imagine what digital characters see and do on set. • This work presents an MR system designed to assist actors during mocap sessions. • The system lets actors use mocap suits and headsets to animate and view characters.

Creating facial animations using 3D computer graphics represents a very laborious and time-consuming task. Among the numberless approaches for animating faces, the use of blendshapes remains the most common solution because of their simplicity and the ability to produce high-quality results. This approach, however, is also characterized by important drawbacks. With the traditional animation suites, to select the blendshapes to be activated animators are generally requested to memorize the mapping between the blendshapes and the influenced mesh vertices; alternatively, they need to adopt a trial-and-error search within the whole library of available blendshapes. Moreover, the level of expressiveness that can be reached may be lower than expected; this is due to the fact that the possibility to apply transformations to vertices different than just linear translations and mechanisms for adding, e.g., exaggerations, are typically not integrated into the same animation environment. To tackle these issues, this article proposes an immersive virtual reality-based interface that leverages sketches for the direct manipulation of blendshapes. Animators can draw both linear and curved strokes, which are used to automatically extract information about the blendshape to be activated and its weight, the trajectories that associated vertices have to follow, as well as the timing of the overall animation. A user study was carried out with the aim of evaluating the proposed approach on several representative animations tasks. Both objective and subjective measurements were collected. Experimental results showed the benefits of the devised interface in terms of task completion time, animation accuracy, and usability.

Technology is disrupting the way films involving visual effects are produced. Chroma-key, LED walls, motion capture (mocap), 3D visual storyboards, and simulcams are only a few examples of the many changes introduced in the cinema industry over the last years. Although these technologies are getting commonplace, they are presenting new, unexplored challenges to the actors. In particular, when mocap is used to record the actors' movements with the aim of animating digital character models, an increase in the workload can be easily expected for people on stage. In fact, actors have to largely rely on their imagination to understand what the digitally created characters will be actually seeing and feeling. This paper focuses on this specific domain, and aims to demonstrate how Augmented Reality (AR) can be helpful for actors when shooting mocap scenes. To this purpose, we devised a system named AR-MoCap that can be used by actors for rehearsing the scene in AR on the real set before actually shooting it. Through an Optical See-Through Head-Mounted Display (OST-HMD), an actor can see, e.g., the digital characters of other actors wearing mocap suits overlapped in real-time to their bodies. Experimental results showed that, compared to the traditional approach based on physical props and other cues, the devised system can help the actors to position themselves and direct their gaze while shooting the scene, while also improving spatial and social presence, as well as perceived effectiveness.

3D sketching in virtual reality (VR) enables users to create 3D virtual objects intuitively and immersively. However, previous studies showed that mid-air drawing may lead to inaccurate sketches. To address this issue, we propose to use one hand as a canvas proxy and the index finger of the other hand as a 3D pen. To this end, we first perform a formative study to compare two-handed interaction with tablet-pen interaction for VR sketching. Based on the findings of this study, we design HandPainter, a VR sketching system which focuses on the direct use of two hands for 3D sketching without requesting any tablet, pen, or VR controller. Our implementation is based on a pair of VR gloves, which provide hand tracking and gesture capture. We devise a set of intuitive gestures to control various functionalities required during 3D sketching, such as canvas panning and drawing positioning. We show the effectiveness of HandPainter by presenting a number of sketching results and discussing the outcomes of a user study-based comparison with mid-air drawing and tablet-based sketching tools.

A common operation performed in Virtual Reality (VR) environments is locomotion. Although real walking can represent a natural and intuitive way to manage displacements in such environments, its use is generally limited by the size of the area tracked by the VR system (typically, the size of a room) or requires expensive technologies to cover particularly extended settings. A number of approaches have been proposed to enable effective explorations in VR, each characterized by different hardware requirements and costs, and capable to provide different levels of usability and performance. However, the lack of a well-defined methodology for assessing and comparing available approaches makes it difficult to identify, among the various alternatives, the best solutions for selected application domains. To deal with this issue, this article introduces a novel evaluation testbed which, by building on the outcomes of many separate works reported in the literature, aims to support a comprehensive analysis of the considered design space. An experimental protocol for collecting objective and subjective measures is proposed, together with a scoring system able to rank locomotion approaches based on a weighted set of requirements. Testbed usage is illustrated in a use case requesting to select the technique to adopt in a given application scenario.

Although passive haptic interfaces have been shown to be capable to enhance the user's sense of presence in Mixed Reality experiences, their use is still constrained by the need to rely on exact replicas of virtual objects or on custom-made devices mimicking the original ones. Unfortunately, the former are not flexible enough in terms of reconfigurability, whereas the latter may be difficult to reproduce. To tackle these issues, this paper explores the possibility to build passive haptic interfaces using off-the-shelf toy construction bricks. Bricks can be assembled to provide the intended feedback in more than one task. Moreover, they may be reassembled in another application to mimic completely new objects and support totally different tasks.

Virtual character animation is receiving an ever-growing attention by researchers, who proposed already many tools with the aim to improve the effectiveness of the production process. In particular, significant efforts are devoted to create animation systems suited also to non-skilled users, in order to let them benefit from a powerful communication instrument that can improve information sharing in many contexts like product design, education, marketing, etc. Apart from methods based on the traditional Windows-Icons-Menus-Pointer (WIMP) paradigms, solutions devised so far leverage approaches based on motion capture/retargeting (the so-called performance-based approaches), on non-conventional interfaces (voice inputs, sketches, tangible props, etc.), or on natural language processing (NLP) over text descriptions (e.g., to automatically trigger actions from a library). Each approach has its drawbacks, though. Performance-based methods are difficult to use for creating non-ordinary movements (flips, handstands, etc.); natural interfaces are often used for rough posing, but results need to be later refined; automatic techniques still produce poorly realistic animations. To deal with the above limitations, we propose a multimodal animation system that combines performance- and NLP-based methods. The system recognizes natural commands (gestures, voice inputs) issued by the performer, extracts scene data from a text description and creates live animations in which pre-recorded character actions can be blended with performer’s motion to increase naturalness.

Software for computer animation is generally characterized by a steep learning curve, due to the entanglement of both sophisticated techniques and interaction methods required to control 3D geometries. This paper proposes a tool designed to support computer animation production processes by leveraging the affordances offered by articulated tangible user interfaces and motion capture retargeting solutions. To this aim, orientations of an instrumented prop are recorded together with animator's motion in the 3D space and used to quickly pose characters in the virtual environment. High-level functionalities of the animation software are made accessible via a speech interface, thus letting the user control the animation pipeline via voice commands while focusing on his or her hands and body motion. The proposed solution exploits both off-the-shelf hardware components (like the Lego Mindstorms EV3 bricks and the Microsoft Kinect, used for building the tangible device and tracking animator's skeleton) and free open-source software (like the Blender animation tool), thus representing an interesting solution also for beginners approaching the world of digital animation for the first time. Experimental results in different usage scenarios show the benefits offered by the designed interaction strategy with respect to a mouse & keyboard-based interface both for expert and non-expert users.

Due to the continuous advancements made in robot technologies, the development of intuitive and effective user interfaces for human-robot interaction is getting increasingly important. This paper investigates how different types of interfaces can be used for allowing a single operator to remotely control a team of robots endowed with different capabilities. Attention is focused on three user interfaces based on a gamepad, on a mobile device and on hand tracking, respectively. To evaluate pros and cons of the above interfaces, a user study was conducted, in which participants had to combine the capabilities of a rover, a drone and a robotic arm in order to carry out a search and pick task. Based on the experiments, the fastest way to complete the task was to use the mobile device. However, results showed that some of the interfaces could provide better performances for selected robots and associated sub-tasks. It is worth observing that, despite evidences about efficiency, participants rated the gamepad as the preferred interface from the point of view of subjective usability.

The players of the digital industry look at network Big Data as an incredible source of revenues, which can allow them to design products, services, and market strategies ever more tailored to users' interests and needs. This is the case of data collected by Web analytics tools, which describe the way users interact with Web contents and where their attention focuses onto during navigation. Given the complexity of information to analyze, existing tools often make use of visualization strategies to represent data aggregated throughout separate sessions and multiple users. In particular, heat maps are often adopted to study the distribution of mouse activity and identify page regions that are more frequently reached during interaction. Unfortunately, since Web contents are accessed via ever more heterogeneous devices, region-based heat maps cannot be exploited anymore to aggregate data concerning user's attention, since the same Web content may move to another page location or exhibit a different aspect depending on the access device used or the user agent setup. This paper presents the design of a visual analytics framework capable to deal with the above limitation by adopting a data collection approach that combines information about regions displayed with information about page structure. This way, the well-known heat map-based visualization can be produced, where interactions can be aggregated on a per-element basis independently of the specific access configuration. Experimental results showed that the framework succeeds in accurately quantifying user's attention and replicating results obtained by manual processing.