Rafael Bidarra

Semantic feature modelling

Abstract Almost all current feature modelling systems are parametric, history-based modelling systems. These systems suffer from a number of shortcomings with regard to the modelling process. In particular, they lack a complete specification of feature semantics, and therefore fail to maintain the meaning of the features during modelling. Also, modelling operations sometimes are hampered by the model history, and occasionally even have ill-defined semantics. In the semantic feature modelling approach presented here, the semantics of features is well defined and maintained during all modelling operations. The result of these operations is independent of the order of feature creation, and is well defined. The specification of feature classes, the structure and functionality of the feature model, in particular the Cellular Model, and the model validity maintenance scheme are described. The advantages and disadvantages of the approach, compared to current feature modelling approaches, are pointed out.

Representation and management of feature information in a cellular model

Many limitations in current feature modelling systems are inherited from the geometric representation they use for the product model. Both a very rigid and a very extensive representation are unsuitable for feature applications, at least if no convenient support is provided to manage the data. This paper describes a cellular representation for feature models that contains all the relevant information to effectively solve a variety of current problems in feature modelling. Much benefit is gained from a coherent integration between shapes of a feature model and cells in the cellular model. Every feature shape has an explicit volumetric representation in terms of cells. Specific subsets of its boundary are also distinguished in terms of cell faces and edges. Feature interactions are maintained in attributes of cells, cell faces and cell edges. Methods for modifying and querying the cellular model are presented, and their application is illustrated for feature validity maintenance, feature interaction management, feature conversion between multiple views, and feature visualization.

Adaptivity Challenges in Games and Simulations: A Survey

In computer games and simulations, content is often rather static and rigid. As a result, its prescripted nature can lead to predictable and impersonal gameplay, while alienating unconventional players. Adaptivity in games has therefore been recently proposed to overcome these shortcomings and make games more challenging and appealing. In this paper, we survey present research on game adaptivity, identifying, and discussing the main challenges, and pointing out some of the most promising directions ahead. We first survey the purposes of adaptivity, as the principles that could steer an adaptation and generation engine. From this perspective, we proceed to thoroughly discuss adaptivitys targets and methods. Current advances and successes in this emerging field point to many yet unexplored research opportunities. Among them, we discuss the use of gameplay expectations, learning preferences, and assessment data in the integrated adaptation of game worlds, scenarios, and quests. We conclude that, among other methods, procedural content generation and semantic modeling can powerfully combine to create offline customized content and online adjustments to game worlds, scenarios, and quests. These and other promising methods, deserving ample research efforts, can therefore, be expected to significantly contribute towards making games and simulations even more unpredictable, effective, and fun.

A Survey on Procedural Modelling for Virtual Worlds

Procedural modelling deals with (semi‐)automatic content generation by means of a program or procedure. Among other advantages, its data compression and the potential to generate a large variety of detailed content with reduced human intervention, have made procedural modelling attractive for creating virtual environments increasingly used in movies, games and simulations. We survey procedural methods that are useful to generate features of virtual worlds, including terrains, vegetation, rivers, roads, buildings and entire cities. In this survey, we focus particularly on the degree of intuitive control and of interactivity offered by each procedural method, because these properties are instrumental for their typical users: designers and artists. We identify the most promising research results that have been recently achieved, but we also realize that there is far from widespread acceptance of procedural methods among non‐technical, creative professionals. We conclude by discussing some of the most important challenges of procedural modelling.

The role of semantics in games and simulations

Powerful graphics hardware is enabling strong improvements in both the appearance and the complexity of virtual worlds for games and simulations. However, current practices in the design and development of virtual worlds mostly resemble high-tech variants of traditional handcrafts, resulting in increasingly unbearable design costs. In this article we state that an essential key to overcoming these problems lies in the enrichment of object models with several kinds of semantic data. We discuss numerous and promising uses for semantic information in virtual worlds, and show, for many of them, how previous results of recent research can be successfully applied. We also identify the fundamental challenges in this new cross-disciplinary area, and point out a number of open issues lying ahead, including the need for (i) a suitable way of specifying semantic data, providing a powerful vocabulary that is useful and usable for all disciplines involved in game design and development; (ii) a seamless integration of semantic data integrated with procedural generation techniques, in order to provide designers with a new and powerful generation of tools; and (iii) a consistency maintenance among evolving objects in a changeable environment, for which powerful constraint-solving methods will be instrumental. We conclude that, as the expectancy for future games and simulations steadily shifts from improved graphics and appearance towards improved character behavior, plausible realism and coherent gameplay, embedding the game world and its objects with richer semantics is going to play a crucial role. We can therefore expect that, in the near future, increasing research efforts and influential results will be emerging in this new exciting area.

Semantic 3D Media and Content: A declarative approach to procedural modeling of virtual worlds

With the ever increasing costs of manual content creation for virtual worlds, the potential of creating it automatically becomes too attractive to ignore. However, for most designers, traditional procedural content generation methods are complex and unintuitive to use, hard to control, and generated results are not easily integrated into a complete and consistent virtual world. We introduce a novel declarative modeling approach that enables designers to concentrate on stating what they want to create instead of on describing how they should model it. It aims at reducing the complexity of virtual world modeling by combining the strengths of semantics-based modeling with manual and procedural approaches. This article describes two of its main contributions to procedural modeling of virtual worlds: interactive procedural sketching and virtual world consistency maintenance. We discuss how these techniques, integrated in our modeling framework SketchaWorld, build up to enable designers to create a complete 3D virtual world in minutes. Procedural sketching provides a fast and more intuitive way to model virtual worlds, by letting designers interactively sketch their virtual world using high-level terrain features, which are then procedurally expanded using a variety of integrated procedural methods. Consistency maintenance guarantees that the semantics of all terrain features is preserved throughout the modeling process. In particular, it automatically solves conflicts possibly emerging from interactions between terrain features. We believe that these contributions together represent a significant step towards providing more user control and flexibility in procedural modeling of virtual worlds. It can therefore be expected that by further reducing its complexity, virtual world modeling will become accessible to an increasingly broad group of users.

Integrating procedural generation and manual editing of virtual worlds

Because of the increasing detail and size of virtual worlds, designers are more and more urged to consider employing procedural methods to alleviate part of their modeling work. However, such methods are often unintuitive to use, difficult to integrate, and provide little user control, making their application far from straightforward. In our declarative modeling approach, designers are provided with a more productive and simplified virtual world modeling workflow that matches better with their iterative way of working. Using interactive procedural sketching, they can quickly layout a virtual world, while having proper user control at the level of large terrain features. However, in practice, designers require a finer level of control. Integrating procedural techniques with manual editing in an iterative modeling workflow is an important topic that has remained relatively unaddressed until now. This paper identifies challenges of this integration and discusses approaches to combine these methods in such a way that designers can freely mix them, while the virtual world model is kept consistent during all modifications. We conclude that overcoming the challenges mentioned, for example in a declarative modeling context, is instrumental to achieve the much desired adoption of procedural modeling in mainstream virtual world modeling.

A Collaborative Feature Modeling System

Collaborative systems are distributed multiple-user systems that are both concurrent and synchronized. An interesting research challenge is to develop a collaborative modeling system that offers all facilities of advanced modeling systems to its users, while at the same time providing them with the necessary coordination mechanisms that guarantee effective collaboration. To achieve this, a web-based collaborative feature modeling system, webSpiff, has been developed. It has a client-server architecture, with an advanced feature modeling system as a basis for the server, providing feature validation, multiple views and sophisticated visualization facilities. A careful distribution of the functionality between the server and the clients has resulted in a well-balanced system. On the one hand, the server offers all the functionality of the original feature modeling system. On the other hand, all desirable interactive modeling functionality is offered by the clients, ranging from display of feature model images to interactive model specification facilities. The architecture of webSpiff, the distribution of model data, the functionality of the server and the clients, and the communication mechanisms are described. It is shown that a good compromise between interactivity and network load has been achieved, and that indeed advanced feature modeling with a collaborative system is feasible. @DOI: 10.1115/1.1521435#

Balancing Play, Meaning and Reality: The Design Philosophy of LEVEE PATROLLER

Most serious games have been developed without a proper and comprehensive design theory. To contribute to the development of such a theory, this article presents the underlying design philosophy of LEVEE PATROLLER, a game to train levee patrollers in the Netherlands. This philosophy stipulates that the design of a digital serious game is a multiobjective problem in which trade-offs need to be made. Making these trade-offs takes place in a design space defined by three equally important components: (a) Play, (b) Meaning, and (c) Reality. The various tensions between these three components result in design dilemmas and trilemmas that make it difficult to balance a serious game. Each type of tension is illustrated with one or more examples from the design of LEVEE PATROLLER.

Interactive GPU-based procedural heightfield brushes

Virtual outdoor terrain used for games is generally created by a level designer, using a variety of tools. These tools are currently based either on local interactive brush-based terrain sculpting or on global, parameterized algorithmic synthesis/adaptation of complete heightfields. Both tool types have largely complementary benefits and drawbacks. In this paper, we present procedural brushes, which combine the strengths of both tool types, offering a seamless transition from local control to fully automated generation, depending on the brush size. To optimize the execution speed of the computationally-intensive procedural algorithms, we propose to use the huge processing power of todays graphics hardware. For this, the procedural algorithms have been translated to shaders, and are used as part of a pipeline to render changes on a heightfield in video memory. We present a GPU brush editing pipeline for graphics hardware supporting Shader Model 3.0, coping with hardware restrictions regarding blend modes, precision and texture size. Several implemented procedural algorithms are described as well, two of which are novel. Experiments showed that the implemented system resulted in a speedup of roughly one order of magnitude over a reference CPU pipeline implementation. This made it possible for users to apply both trivial and complex procedural brushes at interactive rates, thus leading to a more efficient creation of complex virtual worlds.