Section: New Results

Creating and Interacting with Virtual Prototypes

• Scientist in charge: Jean-Claude Léon.

• Other permanent researchers: Marie-Paule Cani, Olivier Palombi, Damien Rohmer, Rémi Ronfard.

The challenge is to develop more effective ways to put the user in the loop during content authoring. We generally rely on sketching techniques for quickly drafting new content, and on sculpting methods (in the sense of gesture-driven, continuous distortion) for further 3D content refinement and editing. The objective is to extend these expressive modeling techniques to general content, from complex shapes and assemblies to animated content. As a complement, we are exploring the use of various 2D or 3D input devices to ease interactive 3D content creation.

Sketch-based modeling and editing of 3D shapes

Participants : Marie-Paule Cani, Arnaud Emilien, Even Entem, Stefanie Hahmann, Rémi Ronfard.

While a lot of work has been done on sketch-based modeling of solid shapes, only a few methods do tackle surface models. Terrain surfaces are particular challenging: their fractal-like distribution of details makes them easy to identify, but these cannot be fully drawn by a user. In our work, users only need to draw the main silhouettes they would like to see from a first person viewpoint (enabling, for instance, an art director to set the background scene behind his actors). We generate a plausible, complex terrain that matches the sketch by deforming an existing terrain model. This is done by analyzing the complex silhouettes with cups and T-junctions in the input sketch and matching them with perceptually close features of the input terrain. The rest of the terrain is seamlessly deformed while keeping its visual complexity and style. This work was presented at Graphics Interface 2014 [29] and extended to enable the combination of silhouettes from multiple viewpoints in the Computer and Graphics journal [12] .

In collaboration with UBC, we introduced the vector graphics complex (VGC), a simple data structure that supports non-manifold topological modeling for 2D vector graphics illustrations. The representation faithfully captures the intended semantics of a wide variety of illustrations, and is a proper superset of scalable vector graphics and planar map representations. VGC nearly separates the geometry of vector graphics objects from their topology, making it easy to deform objects in interesting and intuitive ways, a premise for enabling their animation. This work was published at SIGGRAPH 2014 [4] . We also developed a method for generating 3D animals from a single sketch. This method takes a complex sketch with cups and T-junctions as input (see Figure 12 , and makes use of symmetry hypotheses to analyze it into regions corresponding to the main body and to front and back limbs. The different regions are then automatically reconstructed and blended together using on our implicit modeling methodologies (SCALIS surfaces).

Lastly, we designed a sketch-based interface for authoring illustrative animations. The method makes use of hierarchical motion brushes, a new concept for specifying complex hierarchical motion with a few strokes [28] .

Sketching and Sculpting Motion

Participants : Marie-Paule Cani, Arnaud Emilien, Kevin Jordao.

We extended sculpting methods, which had been restricted so far to homogeneous geometric models of a single dimension, to the handling of complex structured shapes and to the interactive sculpting of animated environments.

We developed the first method enabling to sculpt animated content in extending our previous elastic mutable model approach. Relying on the crowd patches representation for modeling animated crowds, we extended component mutations to space-time content, enabling a user to stretch, bend or assemble populated streets while ensuring that individual character trajectories remain continuous through space and time, as well as plausible. This work, developed within Kevin Jordao's thesis co-advised with Julien Pettré from the Mimetic project-team in Rennes, was published at Eurographics 2014 [7] .

We developed an interactive system for designing complex waterfall scenes: vector elements created by the user (contacts, freefalls and pools) are used to control the procedural creation of complex waterfalls and rivers that match the user intend while ensuring coherent flows and good embedding within the terrain [18] .

Interaction devices and gestural patterns

Participants : Marie-Paule Cani, Rémi Brouet.

Our work on gestural interaction patterns for 3D design has been developed in collaboration with the HCI team from LIG laboratory towards the exploration of 2D multi-touch tables for the placement and deformation of 3D models.

We are also exploring the use of multi-touch tables for the interactive design and editing of 3D scenes. This is the topic of Rémi Brouet's PhD thesis, co-advised with Renaud Blanch from the human-computer interaction group of LIG laboratory. The main challenge here is to find out how to use 2D interaction media for editing 3D content, hence how to intuitively control the third dimension (depth, non-planar rotations, 3D deformations, etc). Our work on this topic started with a preliminary user study enabling us to analyze all possible hand interaction gestures on table-tops, and to explore the ways users would intuitively try to manipulate 3D environments, either for changing the camera position or for moving objects around. We extracted a general interaction pattern from this study. Our implementation enables both seamless navigation and docking in 3D scenes, without the need for any menu or button to change mode. We are currently extending this work to object editing scenarios, where shapes can be bent or twisted in 3D using 2D interaction and automatic mode selection only.