Matisse-Sbim08 - EUROGRAPHICS Workshop on Sketch-Based...

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EUROGRAPHICS Workshop on Sketch-Based Interfaces and Modeling (2008) C. Alvarado and M.- P. Cani (Editors) Matisse : Painting 2D regions for Modeling Free-Form Shapes A. Bernhardt 1 , A. Pihuit 1 , M. P. Cani 1 , L. Barthe 2 1 Grenoble Universities (LJK-CNRS) & INRIA, France 2 University of Toulouse (IRIT-CNRS), France Abstract This paper presents Matisse , an interactive modeling system aimed at providing the public with a very easy way to design free-form 3D shapes. The user progressively creates a model by painting 2D regions of arbitrary topology while freely changing the view-point and zoom factor. Each region is converted into a 3D shape, using a variant of implicit modeling that fits convolution surfaces to regions with no need of any optimization step. We use intuitive, automatic ways of inferring the thickness and position in depth of each implicit primitive, enabling the user to concentrate only on shape design. When he or she paints partly on top of an existing primitive, the shapes are blended in a local region around the intersection, avoiding some of the well known unwanted blending artifacts of implicit surfaces. The locality of the blend depends on the size of smallest feature, enabling the user to enhance large, smooth primitives with smaller details without blurring the latter away. As the results show, our system enables any unprepared user to create 3D geometry in a very intuitive way. Categories and Subject Descriptors (according to ACM CCS) : I.3.5 [Computer Graphics]: Object Modeling(implicit surfaces); I.3.6 [Computer Graphics]: Methodology and techniques(sketch-based interaction). 1. Introduction Designing 3D shapes is not easily accessible to the public: sculpting the model one has in mind from a piece of clay or wood requires some skills, while sketching, if easier, will only provide a single 2D view of the shape. Digital shape modeling, supported by impressive advances in shape rep- resentation and editing, is an interesting alternative. How- ever, standard modeling systems are far from being usable by un-trained users: they usually require some understand- ing of the underlying geometrical representation, are often limited to some indirect control (e.g. manipulating control structures or weight values) and require a tedious training process before mastering the interface. Most novice users would get discouraged before being able to enjoy a creative design task. Recently, systems based on 2D sketching have been pro- posed to ease the modeling of 3D shapes. However, keeping the simplicity of use of real sketches - where 3D somehow emerges from the sketch - without introducing restrictions on the shape being modeled, is very challenging. This pa- per presents a solution where smooth free-form shapes of any topology can be constructed by progressively painting and refining them from different viewpoints. An example is shown in Figure 1 .
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