Collaborative systems are well established solutions for sharing work among people. In computer graphics these workflows are still not well established, compared to what is done for text writing or software development. Usually artists work alone and share their final models by sending files. In this paper we present a system for collaborative 3D digital sculpting. In our prototype, multiple artists concurrently sculpt a polygonal mesh on their local machines by changing its vertex properties, such as positions and material BRDFs. Our system shares the artists' edits automatically and seamlessly merges these edits even when they happen on the same region of the surface. We propose a merge algorithm that is fast-enough for seamless collaboration, respects users' edits as much as possible, can support any sculpting operation, and works for both geometry and appearance modifications. Since in sculpting artists alternatively perform fine adjustments and large scale modifications, our algorithm is based on a multiresolution edit representation that handles concurrent overlapping edits at different scales. We tested our algorithm by modeling meshes collaboratively in different sculpting sessions and found that our algorithm outperforms prior works on collaborative mesh editing in all cases.

Editing spatially-varying appearance is commonplace in most graphics applications. In this paper, we focus on materials whose appearance is described by BRDFs or BSSRDFs, with parameters specified by textures, and with local frame perturbations, namely bump, normal and tangent maps. Editing these materials amounts to editing the textures that encode the spatial variation. To perform these edits, artists commonly adopt imaging softwares since they have rich toolsets and well-understood user interfaces. But editing material parameters as images does not produce consistent results since the parameters' behaviours in their relative spaces are not taken in account. Our goal is to address this issue with a solution that is practical, in that we do not want to change material representation or editing workflow to ensure adoption. We observe that most image editing operations can be written as linear combination of colors. We thus define editing spaces for material parameters such that linear operations in these spaces respect their inherent meaning of the parameters. Transformations to and from editing spaces are non-linear to capture the non-linear behaviour of the parameters. Since GPUs are particularly efficient when executing linear operations, they can be used well with editing spaces. We demonstrate the use of editing spaces to edit microfacet BRDFs and SubEdit BSSRDFs by performing various imaging operations such as layering, linear and non-linear filtering, local and global contrast enhancements, and hardware-accelerated painting.