Disney Effects Using Implicit Surfaces
Agata Opalach, Steve Maddock · 2005
In their wonderful book “Disney Animation: the Illusion of Life” [18], Frank Thomas and Ollie Johnston tell a storyabout traditional animation and how, within a short time, it developed into a new, successful art form. The animatorsat the Walt Disney Studios succeeded in creating characters that “came to life” on cels. This success was madepossible through endless refinement of drawings until a desired emotion was apparent for the audience. As a result ofthese experiments a list of fundamental principles of traditional animation was compiled, which verbalised theexperience gained by the animators at the Walt Disney Studios.These principles have been successfully applied to computer animation. Lasseter [9] describes the creation of “LuxoJr.”, an animation sequence involving an anglepoise lamp that appeals to the audience in the same way as Disneyanimation. In this work, traditional animation principles were applied manually. The fact that an anglepoise lamp waschosen as the character helped the squash and stretch effects to be achieved more easily. It would be difficult togeneralise this method to be used with arbitrary objects. Also, a lot of artistic skill is required which makes it veryhard for an ordinary user to reproduce these effects in a computer animation system. In our system we are attemptingto incorporate some of the traditional animation principles as the default behaviour of implicitly defined objects.Implicit surfaces as a modelling technique were initially described by Blinn (blobby molecules) [2], Nishimura et al.(metaballs) [13] and Wyvill et al. (soft objects) [20, 21]. All three approaches used scalar fields around 3D points tobuild their models. The technique was later generalised for arbitrary skeletal elements [3, 4, 22] and has foundpractical applications in a wide variety of areas. For instance, Tatsumi et al present the use of metaballs in the processof modelling a cod's liver [16], Fujita et al. represent splashing water using metaballs [6], Muraki uses the blobbymodel for volumetric shape description (including human face modelling) [12], Max and Wyvill render corals as softobjects [10] and Payne and Toga model a rat's brain using distance fields [15].Implicit surfaces have also been appreciated in the field of computer animation. Beier from Pacific Data Imagescommented on the usefulness of blobby primitives for character animation [1] and, in Japan, metaballs have beenwidely used for modelling and animating shapes as complex as human anatomy parts [8]. Another use for thetechnique is in visualising deformable material modelled as particles [11, 19] or mass points [17]. The motion ofindividual particles is modelled by physically based simulation using the Newton equations of motion and bymodelling the interaction between the particles (e.g. their reaction to heat). The particles are then treated as skeletalelements (points) and rendered as an implicit surface.Gascuel has developed a method for modelling precise contact between colliding implicit solids [7]. Her method hasbeen used to model a highly deformable material [5], for which the skeletal elements are animated in a generalisedphysically based particle system. The isosurface around skeletons is generated and collisions between objects areprocessed to calculate the resulting deformations during the collisions. This method models inelastic behaviour ofmaterial with fewer particles (skeletal elements) than previous approaches, e.g [11, 19].There has been some work in applying the principles of traditional animation to implicit surfaces. This was done byWyvill who has developed a technique for modelling squash and stretch effects[23]. In this work, the scalar fieldaround skeletal elements is deformed by warping different regions of space so that the implicit surfaces squashes oncontact with the ground and stretches during motion. Effects such as slug-like motion or waves can be achieved bychoosing a suitable warping function.In our approach we use implicit surfaces for character animation and attempt to incorporate the following traditionalanimation principles into the system: Squash and Stretch, Anticipation, Follow Through and Exaggeration. The work