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Interactive Sampling and Rendering for Complex and Procedural Geometry
(The Eurographics Association, 2001) Stamminger, Marc; Drettakis, George; S. J. Gortle and K. Myszkowski
We present a new sampling method for procedural and complex geometries, which allows interactive point-based modeling and rendering of such scenes. For a variety of scenes, object-space point sets can be generated rapidly, resulting in a sufficiently dense sampling of the final image. We present an integrated approach that exploits the simplicity of the point primitive. For procedural objects a hierarchical sampling scheme is presented that adapts sample densities locally according to the projected size in the image. Dynamic procedural objects and interactive user manipulation thus become possible. The same scheme is also applied to on-the-fly generation and rendering of terrains, and enables the use of an efficient occlusion culling algorithm. Furthermore, by using points the system enables interactive rendering and simple modification of complex objects (e.g., trees). For display, hardware-accelerated 3-D point rendering is used, but our sampling method can be used by any other point-rendering approach.
Incremental Updates for Rapid Glossy Global Illumination
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Granier, Xavier; Drettakis, George
We present an integrated global illumination algorithm including non-diffuse light transport which can handle complex scenes and enables rapid incremental updates. We build on a unified algorithm which uses hierarchical radiosity with clustering and particle tracing for diffuse and non-diffuse transport respectively. We present a new algorithm which chooses between reconstructing specular effects such as caustics on the diffuse radiosity mesh, or special purpose caustic textures, when high frequencies are present. Algorithms are presented to choose the resolution of these textures and to reconstruct the high-frequency non-diffuse lighting effects. We use a dynamic spatial data structure to restrict the number of particles re-emitted during the local modifications of the scene. By combining this incremental particle trace with a line-space hierarchy for incremental update of diffuse illumination, we can locally modify complex scenes rapidly. We also develop an algorithm which, by permitting slight quality degradation during motion, achieves quasi-interactive updates. We present an implementation of our new method and its application to indoors and outdoors scenes.
Drawing for Illustration and Annotation in 3D
(Blackwell Publishers Ltd and the Eurographics Association, 2001) Bourguignon, David; Cani, Marie-Paule; Drettakis, George
We present a system for sketching in 3D, which strives to preserve the degree of expression, imagination, and simplicity of use achieved by 2D drawing. Our system directly uses user-drawn strokes to infer the sketches representing the same scene from different viewpoints, rather than attempting to reconstruct a 3D model. This is achieved by interpreting strokes as indications of a local surface silhouette or contour. Strokes thus deform and disappear progressively as we move away from the original viewpoint. They may be occluded by objects indicated by other strokes, or, in contrast, be drawn above such objects. The user draws on a plane which can be positioned explicitly or relative to other objects or strokes in the sketch. Our system is interactive, since we use fast algorithms and graphics hardware for rendering. We present applications to education, design, architecture and fashion, where 3D sketches can be used alone or as an annotation of an existing 3D model.
Structure-Preserving Reshape for Textured Architectural Scenes
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Cabral, Marcio; Lefebvre, Sylvain; Dachsbacher, Carsten; Drettakis, George
Modeling large architectural environments is a difficult task due to the intricate nature of these models and the complex dependencies between the structures represented. Moreover, textures are an essential part of architectural models. While the number of geometric primitives is usually relatively low (i.e., many walls are at surfaces), textures actually contain many detailed architectural elements.We present an approach for modeling architectural scenes by reshaping and combining existing textured models, where the manipulation of the geometry and texture are tightly coupled. For geometry, preserving angles such as oor orientation or vertical walls is of key importance. We thus allow the user to interactively modify lengths of edges, while constraining angles. Our texture reshaping solution introduces a measure of directional autosimilarity to focus stretching in areas of stochastic content and to preserve details in such areas.We show results on several challenging models, and show two applications: Building complex road structures from simple initial pieces and creating complex game-levels from an existing game based on pre-existing model pieces.
Photorealism and Non-Photorealism in Virtual Heritage Representation
(The Eurographics Association, 2003) Roussou, Maria; Drettakis, George; David Arnold and Alan Chalmers and Franco Niccolucci
The area of virtual heritage has long been concentrated on generating digital reconstructions of historical or archaeological artefacts and sites with enough fidelity to be truly accurate representations of their real-world counterparts. In some cases, the advancement of tools and techniques for achieving greater visual realism has distracted from the development of other directions that enhance a virtual experience, such as interactivity, sound or touch. Recent trends in the area of non-photorealistic rendering shift focus to the development of more "believable" environments, while maintaining the accuracy and validity of the visualised data, which is significant for archaeological research. In this paper we argue that it is important to enhance the perception of realism, achieved both through photorealistic and non-photorealistic visualisation approaches, with interactivity. This is illustrated by two example projects which develop prototype virtual environments created for specialists as well as novice users.
A GPU-driven Algorithm for Accurate Interactive Reflections on Curved Objects
(The Eurographics Association, 2006) Estalella, Pau; Martin, Ignacio; Drettakis, George; Tost, Dani; Tomas Akenine-Moeller and Wolfgang Heidrich
We present a GPU-driven method for the fast computation of specular reflections on curved objects. For every reflector of the scene, our method computes a virtual object for every other object reflected in it. This virtual reflected object is then rendered and blended with the scene. For each vertex of each virtual object, a reflection point is found on the reflector s surface. This point is used to find the reflected virtual vertex, enabling the reflected virtual scene to be rendered. Our method renders the 3D points and normals of the reflector into textures, and uses a local search in a fragment program on the GPU to find the reflection points. By reorganizing the data and the computation in this manner, and correctly treating special cases, we make excellent use of the parallelism and stream-processing power of the GPU. In our results we show that, with our method, we can display high-quality reflections of nearby objects interactively.
Efficient Glossy Global Illumination with Interactive Viewing
(Blackwell Publishers Ltd and the Eurographics Association, 2000) Stamminger, Marc; Scheel, Annette; Granier, Xavier; Perez-Cazorla, Frederic; Drettakis, George; Sillion, Francois
The ability to perform interactive walkthroughs of global illumination solutions including glossy effects is a challenging open problem. In this paper we overcome certain limitations of previous approaches. We first introduce a novel, memory- and compute-efficient representation of incoming illumination, in the context of a hierarchical radiance clustering algorithm. We then represent outgoing radiance with an adaptive hierarchical basis, in a manner suitable for interactive display. Using appropriate refinement and display strategies, we achieve walkthroughs of glossy solutions at interactive rates for non-trivial scenes. In addition, our implementation has been developed to be portable and easily adaptable as an extension to existing, diffuse-only, hierarchical radiosity systems. We present results of the implementation of glossy global illumination in two independent global illumination systems.
Outstanding Technical Contributions Award 2007
(The Eurographics Association and Blackwell Publishing Ltd, 2007) Drettakis, George
Image-based Techniques for the Creation and Display of Photorealistic Interactive Virtual Environments
(The Eurographics Association, 2004) Drettakis, George; Roussou, Maria; Tsingos, Nicolas; Reche, Alex; Gallo, Emmanuel; Sabine Coquillart and Martin Goebel
In this paper we introduce an image-based 3D capture process for the creation and display of photorealistic virtual environments (VEs). The resulting VEs aim to realistically recreate existing real-world scenes that can be displayed in a range of immersive VR systems using a high-quality, view-dependent algorithm and further enhanced using advanced vegetation, shadow display algorithms and 3D sound. The scenes, an archaeological site and an urban environment, were chosen according to real-world applications in the areas of urban planning/architecture and cultural heritage education. The users in each case are able to reconstruct or manipulate elements of the VEs according to their needs, as these have been specified through a detailed user requirements survey. Furthermore, a user task analysis and scenario-based approach has been adopted for the design of the virtual prototypes and the evaluation, which is currently underway. This work is being developed in the context of the EU-funded research project CREATE and the first examples of the prototype system in use are described and demonstrated in this paper.
Lazy Solid Texture Synthesis
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Dong, Yue; Lefebvre, Sylvain; Tong, Xin; Drettakis, George
Existing solid texture synthesis algorithms generate a full volume of color content from a set of 2D example images. We introduce a new algorithm with the unique ability to restrict synthesis to a subset of the voxels, while enforcing spatial determinism. This is especially useful when texturing objects, since only a thick layer around the surface needs to be synthesized. A major difficulty lies in reducing the dependency chain of neighborhood matching, so that each voxel only depends on a small number of other voxels.Our key idea is to synthesize a volume from a set of pre-computed 3D candidates, each being a triple of interleaved 2D neighborhoods. We present an efficient algorithm to carefully select in a pre-process only those candidates forming consistent triples. This significantly reduces the search space during subsequent synthesis. The result is a new parallel, spatially deterministic solid texture synthesis algorithm which runs efficiently on the GPU.Our approach generates high resolution solid textures on surfaces within seconds. Memory usage and synthesis time only depend on the output textured surface area. The GPU implementation of our method rapidly synthesizes new textures for the surfaces appearing when interactively breaking or cutting objects.

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