Unity WebGL Limitations

WebGL is supported by the majority of web browsers which makes WebGL Worlds very accessible. Nevertheless, there are few limitations in WebGL itself as a 3D Web technology and in JavaScript as a language for 3D Graphics. JavaScript does not support multithreading or direct access to IP sockets of web browsers for security and privacy concerns. WebGL supports only baked global illumination and not real-time ones. In addition, it does not support procedural materials or linear colour rendering. It supports basic Web audio API which has many limited audio features compared to other platforms. The initial download time of a Unity WebGL world is a lot bigger than that of its plug-in counterpart of the same world due to build sizes being a lot bigger in many instances.

Another concern is the memory used by Unity 3D WebGL builds. First the heap memory which Unity 3D uses to store loaded assets and scenes needs to be at a convenient size to fit all data required to play the content in web browser. Tweaking the WebGL heap memory size avoids many out-of-memory problems encountered normally in big WebGL builds. Another issue related to memory in WebGL is the memory used by the JavaScript engines for parsing and optimising WebGL codes in browsers.

Compression and optimisation techniques of Unity WebGL builds minimise the emitted JavaScript code and thus result in smaller download times and lesser memory consumption. WebGL 2.0 (based on OpenGL ES 3.0) mitigates some of the limitations of WebGL 1.0 but is still experimental and is not yet supported in the majority of web browsers [409, 410].

4.5

Summary

This chapter investigated the QoS of DH WBVWs. QoS metrics were captured for two Unity 3D DH WBVWs which include FPS, FT, CPU, GPU, memory usage and Initial Download Times. Many limitations and bottlenecks found in these environments were identified and discussed and optimizations were proposed.

In the following chapter, 3D Digital Heritage artefacts, another type of 3D Web content used extensively in CH applications and WBVMs, will be investigated.

5

Chapter Five

3D Digital Heritage

Artefacts

Cultural heritage artefacts act as a gateway helping people learn about their social traditions and history. However, preserving these artefacts involves many difficulties, including potential destruction or damage from global warming, pollution, wars and conflicts, and degradation from day to day use. In addition, artefacts can only be present in one place at a time, and many of them can not be exhibited due to the limited physical space of museums. The digital domain offers opportunities to capture and represent the form and texture of these artefacts and to overcome the previously mentioned constraints by allowing people to access and interact with them on multiple devices and network regimes. The first part of this chapter investigates the QoS of DH artefacts mainly by capturing the download and processing times of different 3D models of different resolutions fetched from the Sketchfab web repository. In the second part of the chapter, a preliminary investigation of the perception of Visual Latency of 3D models is reported. Furthermore, the subjective perception of the fidelity of 3D digital heritage artefacts in web browsers is studied through two experiments in order to discover perceptible resolution thresholds. This helps CH stakeholders to create models of reasonable graphical complexity that could be fetched on the biggest range of end devices. It also enables the design of systems which efficiently optimise the user experience by adapting their behaviour based upon users’ perception of fidelity and models’characteristics.

A large proportion of this chapter appeared in the following peer-reviewed publication:

1. Bakri, H., Miller, A., & Oliver, I. (2018, June). Fidelity Perception of 3D Models on the Web. In International Conference on Immersive Learning (pp. 113-130). Springer, Cham. [28].

5.1

Introduction

The work presented in this chapter furthers the knowledge of Cultural Heritage stakeholders of the download and processing times, user perception of visual latency and subjective perception of fidelity of 3D digital heritage models of different levels of detail on a wide range of client devices and network regimes. This knowledge enables us to design digital heritage applications with the aforementioned areas in mind thus meeting the demands of different user bases.

This also paves the way for developing Hannibal, an adaptive engine that strikes the best possible balance between QoS and QoE. Hannibal is presented in Chapter 7. This chapter presents an investigation into the Quality of Service (QoS) and Quality of Experience (QoE) of Web3D Digital Heritage models that are fetched from the Sketchfab social repository on mobile devices and standalone PCs. The aim is to understand responsiveness mainly in terms of Initial Download & Processing Times (IDPTs) of the DH models and to understand the user-based perception of visual latency (a preliminary study conducted in Section 5.3.1) and the subjective perception of fidelity of DH models by users (a study presented in Section 5.3.2 and published in [28]).

The detailed methodological procedures of how to capture the Initial Download and Processing Times (IDPTs) of the digital heritage Web3D models on personal computers and mobile devices are detailed in Chapter 3, Section 3.4.2.1. The subjective perception of fidelity of DH Web3D models is studied through two major experiments. The methodological procedures pertaining to those two experiments are detailed in Chapter 3, Section 3.4.2.2.

The remainder of this chapter is organised as follows: Section 5.2 presents the results and analysis of the QoS empirical studies conducted on DH Web3D models. In addition, this section presents best-practice recommendations following the