An Extensible Simulation Framework Supporting Physically-based Interactive Painting

Abstract

Since the introduction of computers, a lot of effort has gone into the research on applications that enable a user to create images for their artistic value. In case of interactive systems that try to provide a digital equivalent of the traditional painting process, however, most still produce images that appear too artificial and lack the \natural look" and complexity that can be found in real paintings. Especially capturing the ambient behavior of watery paints like watercolor, gouache and Oriental ink, which run, drip and diffuse, is a challenging task to perform in real-time. For this reason, artists still prefer to use traditional methods. The advantages of such a paint system are numerous, however, as it allows to fully exploit the exibility of the digital domain, and perform all sorts of "non-physical" operations. In this dissertation we present a physically-based, interactive paint system that supports the creation of images with watery paint. We mainly target watercolor paint medium, but the model is general enough to simulate also related media like gouache and Oriental ink. In order to create a software system that is easy to maintain, change and extend, we first outline a component-based framework that is able to curb the complexity of building physically-based applications. The framework uses XML to provide a uniform description of the system's composition out of components. The cornerstone of the paint system is embodied by the canvas model, which adopts specialized algorithms, both physically-based and empiricallybased, on three different layers for the purpose of simulating paint behavior. Two implementations of the canvas model are presented: the first relies on a high-performance cluster (HPC) to perform a parallel simulation, while the second uses programmable graphics hardware. The second implementation is extended to a full virtual paint environment: \WaterVerve", which features the Kubelka-Munk diffuse reflectance algorithm for rendering paint, a deformable 3D brush model and a set of artistic tools that fully exploit the physically based nature of the system.