Cyprien Buron

GPU Shape Grammars

GPU Shape Grammars provide a solution for interactive procedural generation, tuning and visualization of massive environment elements for both video games and production rendering. Our technique generates detailed models without explicit geometry storage. To this end we reformulate the grammar expansion for generation of detailed models at the tesselation control and geometry shader stages. Using the geometry generation capabilities of modern graphics hardware, our technique generated massive, highly detailed models. GPU Shape Grammars integrate within a scalable framework by introducing automatic generation of levels of detail at reduced cost. We apply our solution for interactive generation and rendering of scenes containing thousands of buildings and trees.

GPU Roof Grammars

We extend GPU shape grammars [MBG∗12] to model highly detailed roofs. Starting from a consistent roof structure such as a straight skeleton computed from the building footprints, we decompose this information into local roof parameters per input segments compliant with GPU shape grammars. We also introduce Join and Project rules for a consistent description of roofs using grammars, bringing the massive parallelism of GPU shape grammars to the benefit of coherent generation of global structures.

Dynamic on-mesh procedural generation control

Procedural representations are powerful tools to generate highly detailed objects through amplification rules. However controlling such rules within environment contexts (e.g., growth on shapes) is restricted to CPU-based methods, leading to limited performances. To interactively control shape grammars, we introduce a novel approach based on a marching rule on the GPU. Environment contexts are encoded as geometry texture atlases, on which indirection pixels are computed around each chart borders. At run-time, the new rule is used to march through the texture atlas and efficiently jumps from chart to chart using indirection information. The underlying surface is thus followed during the grammar development. Moreover, additional texture information can be used to easily constrain the grammar interpretation. For instance, one can paint directly on the mesh allowed growth areas or the leaves density, and observe the procedural model adapt on-the-fly to this new environment. Finally, to preserve smooth geometry deformation at shape instantiation stage, we use cubic Bezier curves computed using a depth-first grammar traversal.

Grabbing real light: toward virtual presence

Realistic lighting of virtual scenes has been a widely researched domain for decades. Many recent methods for realistic rendering make extensive use of image-based lighting, in which a real lighting environment is captured and reused to light virtual objects. However, the capture of such lighting environments usually requires still scenes and specific capture hardware such as high end digital cameras and mirror balls. In this paper we introduce a simple solution for the capture of plausible environment maps using one of the most widely used capture device: a simple webcam. In order to be applied efficiently, the captured environment data is then filtered using graphics hardware according to the reflectance functions of the virtual surfaces. As the limited aperture of the webcam does not allow the capture of the entire environment, we propose a simple method for extrapolating the incoming lighting outside the webcam range, yielding a full estimate of the incoming lighting for any direction in space. Our solution can be applied to direct lighting of virtual objects in all virtual reality applications such as virtual worlds, games etc. Also, using either environment map combination or semi-automatic light source extraction, our method can be used as a lighting design tool integrated for post-production.