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Time-independent geometrical deformation for elastic contacts

Camille Brunel 1, 2
2 MANAO - Melting the frontiers between Light, Shape and Matter
LaBRI - Laboratoire Bordelais de Recherche en Informatique, Inria Bordeaux - Sud-Ouest, LP2N - Laboratoire Photonique, Numérique et Nanosciences
Abstract : As animated films and series become more and more present in the mainstream entertainment, the artists’ needs are growing in term of fast and intuitive animation tools. Artists not only heavily rely on their imagination and skills to bring digital models to life; they also take inspiration from the physical world to better immerse viewers in their virtual environment.Many objects of our everyday surroundings exhibit elastic deformations when put in contact with others, e.g., a stress ball crushed by a hand, a pillow smashing a head during a pillow fight or a soft ball bouncing on a goal post. They most notably tend to squash inside the contact and to bulge outside of it. Such squashing and bulging effects are essential to communicate plausible deformation while capturing the physical behavior of soft materials in a variety of contexts, such as animated films. This type of deformation is, however, notoriously difficult and tedious to manually reproduce by computer graphics (CG) artists, and existing tools remain limited for artistic use.In practice, such deformations are thus generated through physically based simulation methods. However, due to their time-dependency, physical simulations must be run after the rigging and animation steps, preventing non-linear editing of the 3D scene. Moreover, artists also often resort to cartoonish deformation effects to better convey emotions and thoughts. Such exaggerated effects are difficult to achieve through physical simulations.The main contribution of this thesis is a novel purely geometric deformation framework that assists the artist by resolving local contacts between elastic objects and producing bulge effects in an art-directable way. To achieve a seamless integration within animation workflows, we designed our deformation tool to provide instant feedback to the artist while enabling non-linear editing thanks to a fully time-independent strategy. To produce plausible bulge effects, our method can also preserve the volume exactly, while artistic controls are also possible to explore more exaggerated behaviors. More specifically, starting from multiple meshes in intersection, our deformer first computes the parts of the surfaces remaining in contact, and then applies a procedural displacement controlled by a profile curve. Although our tool processes each frame independently, it achieves temporally continuous deformations with artistic control of the bulge through a small number of pseudo-stiffness parameters. The plausibility of the deformation is further enhanced by anisotropically spreading the volume-preserving bulge. An extension is also proposed to handle self-collisions between adjacent parts of the same object that often occur in character skinning animation.The result of this work is a robust, real-time deformer that can handle complex geometric configurations like a ball squashed by a hand, colliding lips, bending fingers, etc.
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Submitted on : Tuesday, January 11, 2022 - 3:13:33 PM
Last modification on : Wednesday, February 2, 2022 - 3:13:28 AM
Long-term archiving on: : Tuesday, April 12, 2022 - 7:34:46 PM


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  • HAL Id : tel-03521374, version 1


Camille Brunel. Time-independent geometrical deformation for elastic contacts. Image Processing [eess.IV]. Université de Bordeaux, 2021. English. ⟨NNT : 2021BORD0235⟩. ⟨tel-03521374⟩



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