Procedural filters for customization of virtual worlds Tim Tutenel Delft University of Technology Mekelweg 4 2628 CD, Delft, The Netherlands t.tutenel@tudelft.nl Roland van der Linden Delft University of Technology Mekelweg 4 2628 CD, Delft, The Netherlands roland.vanderlinden@hotmail.com Marnix Kraus Delft University of Technology Mekelweg 4 2628 CD, Delft, The Netherlands marnixkraus@hotmail.com Bart Bollen Delft University of Technology Mekelweg 4 2628 CD, Delft, The Netherlands bartbollen@bartbollen.com Rafael Bidarra Delft University of Technology Mekelweg 4 2628 CD, Delft, The Netherlands r.bidarra@tudelft.nl ABSTRACT Designing virtual game worlds is often a long and labor- intensive process. Moreover, when a game world needs to be slightly altered in appearance, the entire process needs to be repeated, or will at least require some repetitious tasks. Ideally, when the same game world is needed under different circumstances (e.g. in another season, before and after a war, in prosperous or poor economic conditions), the designer should be aided in this process using procedural generation techniques. We propose an approach for the specification of procedural filters that describe how (parts of) virtual worlds should be customized to fit a particular situation based on their semantics and the conditions of the situation. This descrip- tion will guide the customization process by triggering and parametrizing, among others, procedural instructions that can change the appearance of the virtual world. We will discuss how the generic nature of this approach, which fa- vors reusability, and its integration with semantics, which increases the intuitiveness of the design process, can elim- inate many of the repetitious tasks involved in performing these actions manually. We describe an implementation of this approach that shows how some simple procedural filters can i) age an urban envi- ronment and simulate the effects of poor living conditions on the look of that environment, and ii) apply a party atmo- sphere to an ordinary office scene. Categories and Subject Descriptors I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism; I.3.6 [Computer Graphics]: Methodology and Techniques—Interaction techniques ; I.6.7 [Simulation Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. PCGames 2011, June 28, Bordeaux, France Copyright 2011 ACM 978-1-4503-0872-4/11/06 ...$10.00. Figure 1: The painting Girl with a pearl earring, by Delft painter Johannes Vermeer; from left to right: original photo, with an emboss filter applied, and with a patchwork filter applied. and Modeling]: Types of Simulation—Gaming Keywords procedural filters; procedural content generation; virtual worlds; semantics 1. INTRODUCTION With the advent of digital photography editing software, e.g. Adobe Photoshop or Google Picasa, the notion of fil- ters has become widely popular. In that context, filters affect an input image in a large variety of predefined, often parameterized, ways, which mostly have an appealing and intuitive semantics. In this way, for instance, one can apply on a photograph, among others, artistic filters (as e.g. fresco or watercolor), stylize filters (as e.g. diffuse or emboss), or texture filters (as e.g. grain or patchwork), as shown in the examples of Figure 1. Inspired by that concept, we introduce in this paper the notion of procedural filters for virtual worlds, which we define as a procedure aimed at being applied on (part of) a virtual world, that modifies the appearance and other contingent visual attributes of its objects, in order to give them a peculiar desired twist. Regardless of whether they are created fully manually or