Title of Invention

A COMPUTER-IMPLEMENTED METHOD FOR DEFORMING A MODEL USING A WRAP AND SYSTEM THEREFOR

Abstract Deformations are applied to a model using a subdivision surface. Given a wrap and model, a subdivision surface is calculated from the wrap. The model is then bound to the subdivision surface. When the wrap is deformed, the subdivision surface is recalculated. The model is then deformed based on changes in the subdivision surface. Binding parameters may be assigned to control vertices in the wrap to control the application of the deformation to the surface.
Full Text Background of the Invention
Field of the Invention
[0001] This invention relates generally to computer graphics and, more specifically, to
wrap deforming a model using subdivision surfaces.
Background Art
[0002] Computers are widely used to model figures, from insects and monsters to human
beings. The basic view of a figure is known as a model. Creating a model requires a lot of time
and effort on the part of a user. In general, a user creates a model by scanning in a three -
dimensional sculpture or by creating a model by hand based on a traditional two -dimensional
drawing. Frequently, a computer-generated (CG) model is represented mathematically by one or
more parametric surfaces. A CG model usually comprises a large number of parametric surfaces
connected together. A parametric surface is a description of a two-dimensional object in three -
dimensional space where every point on the parametric surface can be mapped to a pair of
parameters (u, v). Many types of parametric surfaces are used in CG modeling, such as NURBS
(Non-Uniform Rational B-Splines) surfaces and subdivision surfaces (the latter having a non -
trivial parameterization).
[0003] A parametric surface has a set of control points (also known as control vertices or
"CVs") that define the shape of the surface. When a CV is moved, the surface that is defined by
the CV deforms into a new shape. Thus, a user can change the shape of a model by moving the
CVs that define the model's surfaces. In order to deform a model to a particular shape, a user
often must move a large number of CVs, due to the natural constraints of parametric surfaces.
Moving large numbers of CVs directly, one by one, is time-consuming and not very intuitive.
Instead, users manipulate CVs programmatically through the use of a deformation algorithm
("deformer"). A deformer enables an animator to move CVs indirectly by using a simpler
interface.
[00041 Many types of deformers exist such as, for example, blendshape s, clusters, and
free-form deformers. Free-form deformers partition space into discrete cells. One type of free -
form deformer, a lattice, comprises surrounding a model with a polygonal cubic mesh that is
partitioned into a relatively large number of divisi ons in x, y, and z (hence the name "lattice").
The lattice surrounds the model in such a way that each of the model's CVs falls inside one cell
of the lattice. As the user moves the vertices of the lattice, the cells of the lattice are deformed,
and the CVs located inside the cells get transformed according to a local affine transformation,
eventually placing the CVs in new locations. In this way, a relatively low- resolution lattice can
be used to create broad deformation on a high- resolution model.
[0005] Another type of free-form deformer, a wrap deformer, is similar to a lattice but
uses an arbitrary polygonal mesh of free topology rather than a lattice mesh. The polygonal
mesh, also known as a polywrap, wrap, or cage, acts as a binding domain for the model, such
that the model is bound to the wrap. This binding transmits deformations of the wrap's vertices
to the CVs of the model, thereby deforming the model itself. Deformations of the wrap's vertices
can affect the model's CVs in a variety of ways. One family of wrap deformers creates small
cells in the space surrounded by the wrap and associates the cells with the CVs of a model. The
problem with this type of wrap deformer is that it doesn't scale well with the size of the model.
Large models at high resolution may require a huge number of cells, and the evaluation and
update process of the deformer is very slow and consumes a lot of memory. Conversely, using a
smaller number of cells will introduce discretization artifacts in the model during deformation.
This type of wrap deformer is further described in "Free- form Deformations with Lattices of
Arbitrary Topology" by R. MacCracken and K. Joy, Proceedings of the 23rd International
Conference on Computer Graphics and Interactive Techniques, 1996, pp. 181-190.
[0006] Another family of wrap deformers associates the CVs of a model with certain
CVs on the wrap. The motion of the model's CVs is then defined as a weighted linear
combination of the motions of the wrap's CVs. This approach is faster than the space cell
division approach mentioned above; however, it suffers from many problems and artifacts due to
the simplistic nature of the linear interpolation scheme.
[00071 A wrap can be located either inside or outside of a model. When a wrap is located
inside a model, it acts like a skeleton. As the underlying skeleton changes, the outer layer (the
model) changes also. When a wrap is located outside of a model, it acts like a pupp eteer with
strings connecting the wrap to the model. As the wrap is deformed, the strings pull on the model
and thereby deform the model.
[0008] In order to animate a model, it is necessary to create additional images that show
the model in various poses corresponding to stages of a movement. Each of these images is
identical to the model except for slight differences. For example, the model may have its mouth
closed, while additional images show the model's mouth opening over time. Many images must
be created in order to animate a detailed model. Creating each image by manually editing each
CV of the model is nearly impossible. Not only does it require a great deal of work, it also does
not result in a convincing performance for the animated model because of the a wkwardness of
the interface.
[0009] Instead, animators use software "rigs" to pose models as if they were puppets. A
rig is a set of joints, skeletons, and deformers that attach to a model. Rigs provide the
"machinery" that enables users to animate models. A rig comprises computer modules and
interfaces that enable an animator to move the CVs of the model indirectly, via a much simpler
interface. For example, a rig enables an animator to select a part of a model, such as an eyebrow
or a lip, and use simple user interface widgets, such as buttons and sliders, to move that part of
the model.
[0010] Existing wrap deformation software, such as Maya® from Alias Systems and
SOFTIMAGE®|3D from Avid Technology, Inc., has several disadvantages. One disadvantage is
that deformations of the wrap result in excessive linear interpolation artifacts in the model. The
changes made to the wrap are often discontinuous due to the wrap's lack of resolution, and these
discontinuities end up getting transferred to the model. These artifacts are most noticeable when
there is a significant difference between the resolution of the wrap and the resolution of the
model. This situation is common because wraps are usually low-resolution (not continuous),
whereas models are usually high-resolution (continuous). FIG. 1 shows an example of
discontinuities created by wrap deforming a model using prior art software. Here, the wrap 100
is a low-resolution polygonal mesh and the model 110 is a higher-resolution NURBS (Non-
Uniform Rational B-Splines) plane. FIG. 1 shows the effect on the model 110 of raising the
second row of control vertices in the wrap 100. The artifacts indicate problems with the cell
splitting of the polygonal mesh wrap and problems with the weighted contributions of the wrap
on the control vertices of the model.
[0011] Another disadvantage of prior art software is that it is slow. The slowness is
severe enough to make wrap deformation inadequate for character setup purposes. For example,
it cannot be used for sculpting new blendshapes from existing models, unless the models are very
small and not detailed. When existing software is used to wrap deform a detailed, realistic model,
it runs so slowly that it is virtually unusable for modeling and animation. Since free- form
deformers partition space into discrete cells, the calculations they perform require 0(n3) time,
where n is the number of cells.
[0012] What is needed is a way to wrap deform a model that results in fewer
discontinuities and artifacts and is fast enough to be used for modeling realistic characters and
animating characters using rigs.
Summary of the Invention
[0013] The present invention overcomes the limitations of the prior art by using a
subdivision surface as a binding domain to wrap deform a model. A subdivision surface is
derived from a wrap that has been associated with a model. The subdivision surface is bound to
the model by associating points on the subdivision surface with control vertices of the model. In
response to a change in the position of a control vertex of the wrap, the subdivision surface is
redetermined, and the updated surface locations are used to redetermine the position of the
model's control vertices, thereby deforming the model.
[0014] In one embodiment, the model and wrap are input into a software component
called a polywrap deformation engine. The deformation engine creates a subdivision surface
based on the wrap. The deformation engine then binds the model to the subdivision surface.
When the wrap is deformed, the subdivision surface is recalculated. The model is then deformed
based on the recalculated subdivision surface and the binding between the subdivision surface
and the model.
[0015] Using the polywrap deformation engine to wrap deform a model minimizes the
introduction of linear artifacts during the deformation process. This is because the model and the
subdivision surface to which it is bound have similar resolutions. The deformation engine can
also be used with binding parameters assigned to control vertices in the wrap. The values of
these parameters are propagated to the subdivision surface and affect the deformation of the
model. Thus, usage of a subdivision surface enables both positional continuity and continuity in
values of binding parameters.
[0016] The present invention may be embothed in various forms. In one embodiment, the
present invention is a computer-implemented methodology for deforming a model using
subdivision surfaces. Another embodiment provides a software architecture; yet another
embodiment is a computer system which performs the subdivision method. Another aspect of the
invention is the data representation of a model in combination with subdivision surfaces as stored
in a computer-readable medium. The present invention also has embodiments as computer
program products for carrying out the subdivision method.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[0017] FIG. 1 shows an example of discontinuities created by wrap deforming a model
using prior art software.
[0018] FIG. 2 illustrates a block diagram overview of the use of one embodiment of a
software component for wrap deforming a model.
[0019] FIG. 3 illustrates a flowchart of a method for wrap deforming a model according
to one embodiment of the invention.
[0020] FIGS. 4A and 4B illustrate the effect of the value of the subdivision level
parameter.
[0021] FIGS. 5 A-5C illustrate subdivision using the Loop algorithm.
[0022] FIGS. 6A-6D illustrate subdivision using the Catmull-Clark algorithm.
[0023] FIG. 7 illustrates a polygonal cube mesh surrounding a NURBS sphere model.
[0024] FIG. 8 illustrates a polygonal cube mesh surrounding a NURBS sphere model and
the cube mesh's subdivision mesh, calculated using the Loop algorithm.
[0025] FIG. 9 illustrates a binding between a model and a subdivision mesh formed using
the Loop algorithm.
[0026] FIG. 10 illustrates a binding between a model and a subdivision mesh formed
using the Catmull-Clark algorithm.
[0027] FIG. 11 illustrates the wrap, model, and portions of the subdivision mesh of FIG.
8 in addition to the bindings between the model and the subdivision mesh.
[0028] FIG. 12 illustrates an enlarged view of a portion of FIG. 11.
[0029] FIG. 13 illustrates the polygonal cube mesh, the NURBS sphere model, and the
cube mesh's subdivision mesh of FIG. 8 after deformation of the polygonal cube mesh.
[0030] FIGS. 14A, 14B, and 14C illustrate the effect on a model of the value of the
radius of influence binding parameter.
[0031] FIGS. 15A and 15B illustrate the effect on the bindings between a wrap and a
model of the value of the radius of influence binding parameter.
[0032] FIG. 16 illustrates a flowchart of a method for wrap deforming a model according
to another embodiment of the invention.
[0033] The figures depict a preferred embodiment of the present invention for purposes
of illustration only. One skilled in the art will readily recognize from the following discussion
that alternative embodiments of the structures and methods illustrated herein may be employed
without departing from the principles of the invention described herein.
Detailed Descriptions of the Preferred Embodiments
[0034] FIG. 2 illustrates a block diagram overview of the use of one embodiment of a
software component for wrap deforming a model. FIG. 2 includes a polywrap deformation
engine 200, a model 210, a wrap 220, and a deformed model 230. Polywrap deformation engine
200 is a software component used to wrap deform a model 210. The inputs of the deformation
engine 200 are a model 210 and a wrap 220. The output of the deformation engine 200 is a
deformed model 230. After a user is satisfied with the deformed model 230, the deformed model
230 is further processed in order to add special effects such as lightin g and shadows. For
example, the deformed model 230 may be input into a rendering engine (not shown).
[0035] One of the inputs to polywrap deformation engine 200 is a model 210. The model
210 is the figure that will be deformed. The model 210 may be built using a variety of methods
known to those skilled in the art, such as scanning in a three-dimensional sculpture or creating a
model from scratch based on a traditional two-dimensional drawing using a computer graphics
product such as Maya® from Alias Systems. The model 210 may be, for example, a NURBS
(Non-Uniform Rational B -Splines) surface, a subdivision surface, a curve, a polygonal mesh, or
a combination of the above.
[0036] The other input to the polywrap deformation engine 200 is a wrap 220. The wrap
220 is used to deform the model 210. The wrap 220 may be built using a variety of methods
known to those skilled in the art, such as scanning in a model or creating a wrap from scratch
using a computer graphics product such as Maya® from Alias Systems. Preferably, the wr ap 220
is a polygonal mesh.
[0037] FIG. 3 illustrates a flowchart of a method for wrap deforming a model according
to one embodiment of the invention. Polywrap d eformation engine 200 performs wrap
deformation using a subdivision surface. A subdivision surface is a high- resolution surface
calculated based on a polygonal mesh of arbitrary topology. The lower-resolution mesh is
iteratively subdivided and refined until it becomes a high-resolution surface. Examples of this
process will be discussed below. Subdivision surfaces are C2 continuous (i.e., their second
derivatives are continuous) in the limit of infinite refinement (i.e., after an infinite number of
subdivisions). The "subdivision surface" tha t is bound to the model 210 in this embodiment,
which is called the "subdivision mesh," is a finite resolution representation of the limit surface.
Although the subdivision mesh is of finite resolution, the points within it are located within the
limit subdivision surface. Subdivision surfaces are further described in handouts distributed at
Course 23: Subdivision for Modeling and Animation at the 27th International Conference on
Computer Graphics and Interactive Techniques, New Orleans, Louisiana, 2000.
[0038] How well the subdivision mesh approximates the limit subdivision surface
depends on how many times the mesh has been subdivided. Each time the mesh gets subdivided,
the resolution of its surface increases. In the limit, the resolution approaches that of a subdivision
surface. In one embodiment, the user may control the number of division refinements applied to
the initial wrap 220 by adjusting the value of the "subdivision level" parameter. The larger the
value, the more times the wrap 220 will be subdivided and the higher the sampling of the limit
subdivision surface. FIGS. 4A and 4B illustrate the effect of the value of the subdivision level
parameter. FIGS. 4A and 4B each illustrate a polygonal mesh wrap 220, a NURBS sphere model
210, and a subdivision mesh 400 formed from the wrap 220 . The subdivision mesh 400A in FIG.
4A was formed from a wrap 220 using a lower subdivision level parameter value than was used
to form the subdivision mesh 400B in FIG. 4B. As a result, the subdivision mesh 400B has more
binding sites and will provide a better deformation resolution .
[0039] There are many methods for calculating a subdivision surface. FIGS. 5A-5C
illustrate subdivision using the Loop algorithm. In order to use this algorithm, the original
surface 500 should be a triangular mesh. If the wrap 220 that was input into the polywrap
deformation engine 200 is not a triangular mesh, the wrap 220 can be converted into a triangular
mesh by using a triangulation algorithm such as the Delaunay algorithm. The Delaunay
algorithm is further described in "Primitives for the Manipulation of General Subdivisions and
the Computation of Voronoi Diagrams" by L. Guibas and J. Stolfi, ACM Transactions on
Graphics, Vol.4 No. 2, April 1985, pp. 74-123.
[0040] FIG. 5A illustrates an original surface 500 (here, a two -dimensional triangular
mesh) before Loop subdivision. In the first step, a new vertex ("edge point") 505 is placed on
each original edge 510 in the mesh 500 at a location that is a weighted average. FIG. 5B
illustrates the original surface 500 with the new edge points 505. Each original vertex is then
moved to a new weighted location based on its original position and the new edge points.
Finally, new edges 515 are added to connect each new edge point 505 to its adjacent edge points
505. FIG. 5C illustrates the subdivided surface, which is the original surface 500 with the edge
points 505 and new edges 515. The result is that each triangular face in the original mesh 500
divides into four triangular faces. The resulting mesh is then smoothed based on the centroids of
the new faces. The Loop algorithm is described further in "Smooth Subdivision Surfaces Based
on Triangles" by C. T. Loop, Master's thesis, University of Utah, Department of Mathematics,
1987.
[0041] FIGS. 6A-6D illustrate subdivision using the Catmull-Clark algorithm. Unlike the
Loop algorithm, the Catmull-Clark algorithm can be used with any arbitrary mesh, as long as it is
a manifold. FIG. 6A illustrates an original surface 600 (here, a two-di mensional square mesh)
before Catmull-Clark subdivision. In the first step, a new vertex ("face point") 605 is placed at
the center of each face 610 in the original surface 600. FIG. 6B illustrates the original surface
600 with the new face points 605. Then, a new vertex ("edge point") 615 is placed on each
original edge 620 in the mesh 600 at a location that is a weighted average of the center of the
edge 620 and the surrounding new face points 605 . FIG. 6C illustrates the original surface 600
with the face points 605 and the new edge points 615. New edges 625 are then added to connect
each new edge point 615 to its adjacent face points 605. Each vertex in the original surface 600
is then placed at a new position that is a weighted average based on the vertex's surrounding new
face points 605 and new edge points 615. FIG. 6D illustrates the subdivided surface, which is the
original surface 600 with the face points 605, edge points 615, and new edges 625. The result is
that each square face 610 in the original mesh 600 divides into four square faces. The resulting
mesh is then smoothed based on the centroids of the new faces. The Catmull-Clark algorithm is
described further in "Recursively Generated B- Spline Surfaces on Arbitrary Topological
Meshes" by E. Catmull and J. Clark, Computer- Aided Design, 10(6), pp.350-355, November
1978.
[0042] Instead of using a polygonal mesh wrap 220 as the binding domain for the model
210, as in the prior art, polywrap deformation engine 200 uses a subdivision surface as the
binding domain. Recall that traditional wrap deformation, where a model 210 is bound to a
polygonal mesh wrap 220, introduces discontinuities into the model 210 because of the
significant difference between the resolution of the wrap 220 and the resolution of the model
210. Unlike polygonal meshes, subdivision surfaces have arbitrarily high resolutions. Thus,
when a high-resolution model 210 is wrap deformed by a subdivision surface, fewer
discontinuities are introduced into the model 210.
[0043] However, a subdivision surface is generally not deformed directly. Recall that a
subdivision surface is calculated based on a lower- resolution mesh. Thus, polywrap deformation
engine 200 calculates a subdivision mesh 400 based on the wrap 220 and then binds the model
210 to the subdivision mesh 400. The subdivision mesh 400 thereby acts as a proxy, conveying
deformation information from the wrap 220 to the model 210. Since the subdivision mesh 400 is
calculated based on the wrap 220, any deformation in the wrap 220 is automatically propagated
to the subdivision mesh 400. The deformation of the subdivision mesh 400 is then propagated to
the model 210 because of the binding between the model 210 and the subdivision mesh 400.
[0044] In other words, discontinuous changes in the wrap 220 get transformed in to
smooth and continuous changes on the subdivision surface . As a result, binding a model 210 to a
subdivision surface and then deforming the subdivision surface does not introduce as many
discontinuities into the model 210. The result is that fewer discon tinuities are introduced into the
model 210 during the wrap deformation process.
[0045J As discussed above, the closer in resolution the model and subdivision mesh are,
the fewer discontinuities are introduced during the deformation process. When there is a large
difference between the resolution of the wrap and the resolution of the model, it is beneficial to
use a high subdivision level to increase the resolution of the subdivision mesh in order to obtain
a more accurate binding. If the resolution difference is small, then a low subdivision level should
be sufficient.
[0046] For simplicity purposes, the invention will be described in an embodiment for
deforming a NURBS model 210, for example a sphere, using a polygonal cube mesh as a wrap
220. However, the invention may be used to deform a model of any shape or to deform groups of
shapes. Similarly, the wrap may be any shape. FIG. 7 illustrates a polygonal cube mesh
surrounding a NURBS sphere model. FIG. 7 also illustrates several CVs 700 of the model 210.
[0047| When method 300 begins, a model 210 and a wrap 220 have been input into the
polywrap deformation engine 200. The first step of method 300 is to calculate 310 a subdivision
mesh based on the wrap 220, using any of the methods discussed above. In general, Catmull-
Clark subdivision is helpful when deforming NURBS models, since Catmull-Clark subdivision
surfaces and NURBS are similar in topology. Loop subdivision is helpful when deforming cloth
simulations, since cloth and other dynamic simulations frequently use triangulated meshes,
which have a similar topology to Loop subdivision surfaces. Although the polygonal cube mesh
has discontinuities on its surface, the subdivision algorithm transforms it into a smooth,
continuous surface (in the limit). Since the vertices in the subdivision mesh are located in the
limit subdivision surface, artifacts deriving from the finite subdivision of the polygonal mesh are
avoided.
[0048] FIG. 8 illustrates a polygonal cube mesh surrounding a NURBS sphere model and
the cube mesh's subdivision mesh, calculated using the Loop algorithm. Once the deformation
engine 200 has calculated 310 the subdivision mesh 400 based on the wrap 220, the polywrap
deformation engine 200 binds 320 the model 210 to the subdivision mesh 400 (the binding
domain). The binding domain comprises a number of binding sites to which the CV s 700 of the
model 210 are bound. Since the subdivision mesh 400 is a finite resolution representation of the
subdivision limit surface, there are a finite number of binding sites on the subdivision mesh 400.
In one embodiment, the number o f binding sites on the subdivision mesh 400 is controlled by the
subdivision level parameter discussed above.
[0049| Each CV 700 on the model 210 is bound to one binding site on the subdivision
mesh. Alternatively, one CV 700 could be bound to more than one binding site 900, as long as a
normalized weighted averaging of the binding sites on the subdivision surface were defined . In
one embodiment, a CV 700 is bound to the closest binding site; however, many other methods of
binding are also possible. Since a CV of a model 210 is bound to a binding site on the
subdivision mesh 400, the link between them (and thus the link between their deformations) is
surface-based, not volume-based as it is in some prior art.
[0050] Which part of the subdivision mesh 400 is used as the actual binding site depends
on how the subdivision mesh 400 is calculated. FIG. 9 illustrates a binding between a model and
a subdivision mesh formed using the Loop algorithm. Here, a binding site 900 is defined as one
triangular face of the subdivision mesh 400. Each CV (C,) on the model 210 is bound to the
closest binding site 900 of the subdivision mesh 400. In order to determine to which binding site
900 a particular CV 700 is bound, a local reference frame of coordinates is created. Many
choices exist for the local reference frame. In one embodiment, the local reference frame
comprises an origin point O (the center of reference) and three vectors b1, b2, b3. While O can be
any point that lies on the subdivision surface, in o ne embodiment, O is the barycenter (center of
gravity) of the binding site 900. Vector b3 is normal to the subdivision surface and intersects the
subdivision surface at O. Vector b3 is calculated by taking the cross-product of vector b1 and
vector b2. These two vectors go from O to the two nearest consecutive vertices of the binding site
900. If the triangle of the binding site 900 is degenerate, then that binding site is not used. In
FIG. 9, control vertex C0 is bound to the barycenter O of the binding site 900.
[0051] FIG. 10 illustrates a binding between a model and a subdivision mesh formed
using the Catmull-Clark algorithm. In this embodiment, a binding site 900 is defined as a vertex
of the limit subdivision surface. However, many other methods of binding are also possible.
Each CV (C) on the model 210 is bound to the closest vertex of the subdivision mesh 400.
Vectors b1 and b2 are tangent vectors to the limit surface at O. Vector b3 is again defined as the
cross-product of vectors b1 and b2.
[0052] Once the binding site's reference frame {O; bt, b2, bi} has been established, the
binding projection coordinates {,x,,,y„ z,-} of a CV (C,) on the model can be determined. The
binding projection coordinates are the components of the projection of the vector 0-C, onto the
binding site 900. The binding procedure is repeated for each CV in the model 210. Once a
binding has been calculated for each CV in the model 210, the result is a set of local frames of
coordinates (one for each binding site) and the corresponding projections of these coordinates to
the model's control vertices.
[0053] FIG. 11 illustrates the wrap, model, and portions of the subdivision mesh of FIG.
8 in addition to the bindings between the model and the subdivision mesh. Only binding sites
900 that have been bound to CVs 700 on the model 210 are shown. In this embodiment, each CV
on the model was bound to the binding site that contained the nearest barycenter to the CV. FIG.
12 illustrates an enlarged view of a portion of FIG. 11.
[0054] After the polywrap deformation engine 200 has calculated the default bindings
between the model 210 and the subdivision mesh 400, a user can manu ally edit the bindings to
adjust the deformations more precisely in a specific area. Wrap deformers have trouble with
bindings located in tight corners, such as between two fingers or at the corners of mouths and
eyes. In these areas, it is often useful to edit the bindings of a few CVs of the model 210. This
gives the user more control over the binding mechanism between the model 210 and the
subdivision mesh 400. The user can therefore rebind the CVs of the model 210 to different
locations, and the deformation engine 200 will automatically determine new projection
coordinates.
[0055] Once the bindings between the model 210 and the subdivision mesh 400 have
been determined, the binding projection coordinates for each CV 700 of the model 210 are stored
330. These coordinates are later used to transfer deformations of the wrap 220 to the model 210,
as will be discussed below.
[0056] After the binding projection coordinates have been stored 330, the next step is to
deform 340 the wrap 220. The wrap 220 can be deformed 340 in many ways, by either directly
moving its vertices or applying other existing deformers. Since there is only one wrap 220
associated with the deformation engine 200, all changes applied to the wrap 220 transfer a
deformation directly to the model 210. Similarly, any editing of the wrap 220 that causes a
change of the topology of the subdivision mesh 400, such as face extrusion and insert ion and
deletion of edges, triggers a "rebinding" of the model 210 to the wrap 220. Essentially, the
deformation engine 200 detects the topology change, calculates a new subdivision surface and
new binding sites, and reconnects the current state of the model 210 to the subdivision binding
domain. In prior art software, the wrap 220 has two copies, one for the "base" wrap, whic h
defines the binding properties, and another for the "editable" binding wrap. However, prior art
software does not support topological changes to the wrap 220. Users can change only the vertex
positions of the "editable" wrap 220.
[0057] After the wrap 220 has been deformed 340, the next step is to propagate these
changes to the subdivision surface by recalculating the subdivision surface based on the
deformed wrap 220. No matter how the original vertices of the wrap 220 are deformed, the
wrap's subdivision surface always remains smooth and continuous. The recalculation of the
subdivision surface is very fast, much faster than the partitioning of space in three -dimensional
cells that is used by prior art free-form deformers. FIG. 13 illustrates the polygonal cube mesh,
the NURBS sphere model, and the cube mesh's subdivision mesh of FIG. 8 after deformation of
the polygonal cube mesh.
[0058] Recall that the first time that the subdivision surface was calculated (step 310), the
next step was to bind the model 210 to the subd ivision mesh 400. At this point, however, the
model 210 has already been bound to the subdivision mesh 400, and those binding projection
coordinates have been stored. The idea here is to use the recalculated subdivision surface and the
stored bindings to move the CVs 700 of the model 210. Thus, the next step is to deform the
model 210 by calculating 360 new positions of the control vertices 700 of the model 210. As
mentioned above, this calculation is based on the recalculated subdivision surface (and its
associated subdivision mesh 400), the stored binding projection coordinates, and any binding
parameters.
[0059] Since the recalculated subdivision surface has the same resolution as the original
subdivision surface, it has the same number of binding sites 900. However, the reference frame
{O; b1, b2, b3} of each binding site 900 is affected, since the location of O and the orientation of
b1, b2, b3 are translated due to the deformation. In contrast, the binding projection coordinates of
each CV 700 of the model 210 remain constant. The original binding coordinates and the new
reference frame, along with the binding parameters discussed below, enable the prediction of the
new location of a CV 700 on the model 210.
[0060] Binding parameters may include, for example, radius o f influence, weighting, and
blending. While binding parameter values are originally set for a wrap 220, these values are
propagated to the subdivision surface based on the wrap 220. Since the subdivision surface is
continuous, the parameter value changes over the subdivision surface are also continuous, and
this continuity extends to the model 210. Parameter continuity in the model enables a smoother
animation of the underlying model 210, thereby creating a more nuanced performance by the
animated character. Thus, usage of a subdivision surface enables both positional continuity and
continuity in binding parameters.
[0061] The radius of influence parameter affects a binding site 900, and its value can be
set by default or specified by a user. The value of the radius of influence parameter indicates
which CVs 700 of the model 210 can be bound to the binding site 900. Any CV 700 that is
farther away from the binding site 900 than the parameter value will not be bound to the binding
site 900.
[0062] FIGS. 14A, 14B, and 14C illustrate the effect on a model of the value of the
radius of influence binding parameter. FIGS. 14A, 14B, and 14C each illustrate a polygonal
plane mesh 220 and a NURBS plane model 210. In FIG. 14A, the wrap 220 and the model 210
are in their original positions. In FIGS. 14B and 14C, two rows of the wrap 220 have been
translated vertically, resulting a deformation of the model 210. The deformation of the model
210 in FIG. 14B was formed from a wrap 220 having a higher radius of influence binding
parameter value than the wrap 220 used to deform the model 210 in FIG. 14C. As a result, the
deformation in the model 210 in FIG. 14C is more localized.
[0063] The radius of influence parameter changes the bindings between the wrap 220 and
the model 210, as shown more clearly by FIGS. 15A and 15B. FIGS. 15A and 15B illustrate the
effect on the bindings between a wrap and a model of the value of the radius of influence binding
parameter. FIGS. 15A and 15B illustrate the same wraps 220 and models 210 as in FIGS. 14B
and 14C, respectively, as well as the bindings 1500 between the wraps 220 and models 210. As
illustrated, the bindings 1500 in FIG. 15A extend further from the wrap 220 to more distant parts
of the model 210 than do the bindings 1500 in FIG. 15B.
[0064] Another parameter is rate of deformation, also known as weighting. In general, all
points in a wrap 220 deform the underlying model 210 with the same strength. However, a user
may want to vary how strongly a given control vertex or group of control vertices of the wrap
220 affects (pushes or pulls) the model 210. This can be achieved by assigning a weight to the
vertex of the wrap 220. The greater the weight, the stronger the effect of the control vertex on the
model 210. If weights are assigned to the wrap 220, the wrap 220 can be used again with a
different model 210 to produce the same deformation effect. In order to use the wrap 220 with a
different model 210, the binding between the subdivision mesh 400 and the new model 220 is
first established by the method described above (step 320). Prior art software does not support
placing weights on a wrap 220. Instead, weights are placed directly on a model 210.
[0065] The blending parameter determines to what extent a CV in a wrap 220 is
influenced by its current position when the wrap 220 is subjected to a deformation. If the
blending parameter value is low, the new position of the CV will be based mainly on its previous
(neutral) position, with some influence from its calculated pure deformed position (e.g., via a
linear interpolation between the two positions). If the blending parameter value is high , the new
position of the CV will be based mainly on its calculated pure deformed position, with some
influence from its previous (neutral) position.
[0066] Other binding parameters may include elasticity of deformation, color, and mass
or inertia (to affect the model's dynamic behavior).
[0067] Once the new positions of the CVs 700 on the model 210 have been calculated
360, the computer recalculates the model 210 using these new positions, as discussed above with
reference to manual manipulation of CVs.
[0068] A user can also request a rebinding of a model to a subdivision surface. Rebinding
comprises recalculating the subdivision mesh 400 (if needed), rebinding the model 210 to the
subdivision mesh 400, and storing the binding projection coord inates. A user may want to rebind
a model 210 if, for example, the user has changed the value of the subdivision level parameter,
edited the wrap 220 (e.g., by adding a face or removing an edge), or changed the value of a
binding parameter. Alternatively, a user may want to replace the original wrap 220 or the
original model 210 with a different wrap or model, respectively.
[0069] The embodiments described above use one wrap 220. However, it is sometimes
useful to use two wraps 220: a reference wrap to which a model 210 is bound and an editable (or
"live") wrap that provides current binding site information to use when updating the CVs of a
model 210. The editable wrap is identical to the reference wrap except for the locations of its
coordinates. In this embodiment, two subdivision surfaces are computed. The subdivision surface
computed from the reference wrap is used to compute bi nding sites 900, while the subdivision
surface computed from the editable wrap is used to determine the current locations of the binding
sites 900 for each CV of the model 210. The binding frames of coordinates from the latter
subdivision surface and the binding projection coordinates from the former subdivision surface
are used to calculate the new coordinates of the CVs of the model 210.
[0070] In one embodiment, both the reference wrap and the editable wrap can be moved
and edited simultaneously. Moving the reference wrap displaces the area of influence along the
model 210, having binding sites 900 slide through the model 210. Moving the editable wrap
introduces local deformations to the model 210.
[00711 FIG. 16 illustrates a flowchart of a method for wrap deforming a model according
to another embodiment of the invention. In the first step, a subdivision surface is calculated 1610
from the reference wrap. Then, bindings are created 1620 from the model 210 to the subdivision
surface calculated in step 1610. A second subdivision surface is then calculated 1630 from the
editable wrap. This subdivision surface is then used to update 1640 binding projection
coordinates. Finally, the locations of the CVs of the model 210 are calculated, and the deformed
model is output 1650.
[00721 The present invention has been described in particular detail with respect to one
possible embodiment. Those of skill in the art will appreciate that the invention may be
practiced in other embodiments. First, the particular naming of the components, capitalization of
terms, the attributes, data structures, or any other programming or structural aspect is not
mandatory or significant, and the mechanisms that implement the invention or its features may
have different names, formats, or protocols. Further, the system may be implemented via a
combination of hardware and software, as described, or entirely in hardware elements. Also, the
particular division of functionality between the various system components described herein is
merely exemplary, and not mandatory; functions performed by a single system component may
instead be performed by multiple components, and functions performed by multiple components
may instead performed by a single component.
[0073] Some portions of above description present the feature of the present invention in
terms of algorithms and symbolic representations of operations on information. These
algorithmic descriptions and representations are the means used by those skilled in the data
processing arts to most effectively convey the substance of their work to others skilled in the art.
These operations, while described functionally or logically, are understood to be implemented by
computer programs, which are stored in computer readable mediums. Furthermore, these
arrangements of operations can be equivalently referred to as modules or code devices, without
loss of generality.
[0074J It should be borne in mind, however, that all of these and similar terms are to be
associated with the appropriate physical quantities and are merely convenient labels applied to
these quantities. Unless specifically stated otherwise as apparent from the following discussion,
it is appreciated that throughout the description, discussions utilizing terms such as "calculating"
or "determining" or the like, refer to the action and processes of a computer system, or similar
electronic computing device, that manipulates and transforms data represented as physical
(electronic) quantities within the computer system memories or registers or other such
information storage, transmission or display devices.
[0075] Certain aspects of the present invention include process steps and instructions
described herein in the form of an algorithm. It should be noted that the process steps and
instructions of the present invention could be embothed in software, firmware or hardware, and
when embothed in software, could be loaded to reside on and be operated from different type of
computing platforms.
[0076] The present invention also relates to an apparatus for performing the operations
herein. This apparatus may be specially constructed for the required purposes, or it may
comprise a general-purpose computer selectively activated or reconfigured by a computer
program stored in the computer. Such a computer program may be stored in a c omputer readable
storage medium, such as, but is not limited to, any type of disk including floppy disks, optical
disks, CD-ROMs, magnetic-optical disks, read-only memories (ROMs), random access
memories (RAMs), EPROMs, EEPROMs, magnetic or optical cards, application specific
integrated circuits (ASICs), or any type of media suitable for storing electronic instructions, and
each coupled to a computer system bus. Furthermore, the computers referred to in the
specification may include a single processor or m ay be architectures employing multiple
processor designs for increased computing capability.
[0077] The algorithms and illustrations presented herein are not inherently related to any
particular computer or other apparatus. Various general -purpose systems may al so be used with
programs in accordance with the teachings herein, or it may prove convenient to construct more
specialized apparatus to perform the required method steps. The required structure for a variety
of these systems will appear from the description above. In addition, the present invention is not
described with reference to any particular programming language. It is appreciated that a variety
of programming languages may be used to implement the teachings of the present invention as
described herein, and any references to specific languages are provided for disclosure of
enablement and best mode of the present invention.
[0078] The present invention is well-suited to a wide variety of computer network
systems over numerous topologies. Within this field , the configuration and management of large
networks comprise storage devices and computers that are communicatively coupled to
dissimilar computers and storage devices over a network, such as the Internet.
[0079[ Finally, it should be noted that the language used in the specification has been
principally selected for readability and instructional purposes, and may not have been selected to
delineate or circumscribe the inventive subject matter. Accordingly, the disclosure of the present
invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set
forth in the following claims.
We claim :
1. A computer-implemented method for deforming a model (210) using a wrap
(220), the method involving the steps of:
determining a subdivision surface based on the wrap (310);
binding the model to the subdivision surface (320);
updating the subdivision surface responsive to a change in position of a
control vertex in the wrap (350); and
determining a new position of a control vertex of the model responsive to
an update of the sub-division surface (360).
2. The method as claimed in claim 1 involving the step of:
determining a new position for another point of the model (210) based on
a new position of a control vertex on the model.
3. The method as claimed in claim 1, involving the step of determining a set of
binding projection coordinates for a control vertex of the model (330).
4. The method as claimed in claim 1 involving the step of determining a subdivision
mesh, the subdivision mesh (400A) being a finite resolution representation of the
subdivision surface, and wherein binding the model to the subdivision surface involves
binding the model to the subdivision mesh (320).
5. The method as claimed in claim 4 wherein a level of resolution of the subdivision
mesh varies.
6. The method as claimed in claim 4 wherein the step of binding the model (210) to
the subdivision mesh (400A) involves the step of determining, for a control vertex of the
model, at least one binding site of the subdivision surface, the binding site being one of a
vertex of the subdivision mesh and a face of the subdivision mesh.
7. The method as claimed in claim 6 wherein the control vertex of the model (210) is
a control vertex that is closest to the intersection of the model and a vector that is
orthogonal to the subdivision surface at the binding site.
8. The method as claimed in claim 1 wherein the step of binding the model (210) to
the subdivision surface involves the step of determining, for a control vertex of the
model, at least one binding site of the subdivision surface.
9. The method as claimed in claim 8 wherein the step of determining, for a control
vertex of the model (210), at least one binding site of the subdivision surface involves the
step of determining whether the control vertex is farther away from the binding site than
a particular value, the particular value being associated with the binding site.
10. The method as claimed in claim 9 involving the step of assigning at least one
value to the subdivision surface based on the value associated with the binding site.
11. The method as claimed in claim 1 wherein binding the model (210) to the
subdivision surface involves the step of binding a control vertex of the model to a
particular binding site responsive to receiving input from a user.
12. The method as claimed in claim 1, involving the steps of:
assigning a weight value to a control vertex of the wrap (220); and
assigning a weight value to the subdivision surface based on the weight
value assigned to the control vertex of the wrap
wherein determining a new position of a control vertex of the model (210)
is further responsive to a weight value of the subdivision surface.
13. The method as claimed in claim 1 wherein the wrap (220) is a polygonal mesh.
14. The method as claimed in claim 1 wherein the model (210) involves the step of a
NURBS (Non-Uniform Rational B-Splines) model.
15. The method as claimed in claim 1 wherein the step of determining a subdivision
surface based on the wrap (220) involves performing Catmull-Clark subdivision on the
wrap.
16. The method as claimed in claim 1 wherein the step of determining a subdivision
surface based on the wrap (220) involves performing Loop subdivision on the wrap.
17. A system for deforming a model (210) using a wrap (220), the system comprising:
means for determining a subdivision surface based on the wrap (310);
means for binding the model to the subdivision surface (320);
means for updating the subdivision surface responsive to a change in
position of a control vertex in the wrap (350); and
means for determining a new position of a control vertex of the model
responsive to an update of the subdivision surface (360).
18. The system as claimed in claim 17, having means for determining a new position
for another point of the model (210) based on a new position of a control vertex on the
model.
19. The system as claimed in claim 17, having means for determining a subdivision
mesh (400A), the subdivision mesh being a finite resolution representation of the
subdivision surface, and wherein binding the model (210) to the subdivision surface
involves binding the model to the subdivision mesh (320).
20. The system as claimed in claim 19 wherein a level of resolution of the subdivision
mesh varies.
21. The system as claimed in claim 19 wherein binding the model (210) to the
subdivision mesh (400A), is adapted to determine, for a control vertex of the model, at
least one binding site of the subdivision surface, the binding site being one of a vertex of
the subdivision mesh and a face of the subdivision mesh.
22. The system as claimed in claim 21 wherein the control vertex of the model (210)
is a control vertex that is closest to the intersection of the model and a vector that is
orthogonal to the subdivision surface at the binding site.

Documents:

848-kol-2004-abstract.pdf

848-kol-2004-assignment.pdf

848-kol-2004-claims.pdf

848-KOL-2004-CORRESPONDENCE-1.1.pdf

848-kol-2004-correspondence-1.2.pdf

848-kol-2004-correspondence.pdf

848-kol-2004-description (complete).pdf

848-kol-2004-drawings.pdf

848-kol-2004-examination report.pdf

848-kol-2004-form 1.pdf

848-kol-2004-form 18.pdf

848-kol-2004-form 2.pdf

848-kol-2004-form 3-1.1.pdf

848-kol-2004-form 3.pdf

848-kol-2004-form 5.pdf

848-KOL-2004-FORM-27.pdf

848-kol-2004-gpa.pdf

848-kol-2004-granted-abstract.pdf

848-kol-2004-granted-claims.pdf

848-kol-2004-granted-description (complete).pdf

848-kol-2004-granted-drawings.pdf

848-kol-2004-granted-form 1.pdf

848-kol-2004-granted-form 2.pdf

848-kol-2004-granted-specification.pdf

848-kol-2004-petition under rule 137.pdf

848-kol-2004-reply to examination report.pdf

848-kol-2004-specification.pdf

848-kol-2004-translated copy of priority document.pdf


Patent Number 250116
Indian Patent Application Number 848/KOL/2004
PG Journal Number 49/2011
Publication Date 09-Dec-2011
Grant Date 07-Dec-2011
Date of Filing 22-Dec-2004
Name of Patentee Dream Works LLC
Applicant Address 1000 FLOWER STREET, GLENDALE, CALIFORNIA
Inventors:
# Inventor's Name Inventor's Address
1 SEPULVEDA MIGUEL A 10725 ROSE AVENUE, #111 LOS ANGELES, CALIFORNIA 90034
PCT International Classification Number A61F 5/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 10/769,154 2004-01-29 U.S.A.