CN115049768A - Method, apparatus, computer device and storage medium for creating character animation model - Google Patents

Method, apparatus, computer device and storage medium for creating character animation model Download PDF

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CN115049768A
CN115049768A CN202210984057.4A CN202210984057A CN115049768A CN 115049768 A CN115049768 A CN 115049768A CN 202210984057 A CN202210984057 A CN 202210984057A CN 115049768 A CN115049768 A CN 115049768A
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finite element
mesh
vertex
skin
skeleton
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CN115049768B (en
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陆树梁
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Shenzhen Zesen Software Technology Co ltd
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    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T13/00—Animation
    • G06T13/20—3D [Three Dimensional] animation
    • G06T13/40—3D [Three Dimensional] animation of characters, e.g. humans, animals or virtual beings
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T17/00—Three dimensional [3D] modelling, e.g. data description of 3D objects
    • G06T17/20—Finite element generation, e.g. wire-frame surface description, tesselation
    • G06T17/205—Re-meshing

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Abstract

The application relates to a method and a device for creating a character animation model, computer equipment and a storage medium. The method comprises the following steps: acquiring a finite element grid, a skin grid and a skeleton grid, wherein the finite element grid comprises a muscle fiber direction; obtaining skin vertex centroid interpolation weight according to the position information of the vertices of the skin mesh and the skin vertex finite element units, realizing embedding the skin mesh into the finite element mesh, obtaining skeleton vertex centroid interpolation weight according to the position information of the vertices of the skeleton mesh and the skeleton vertex finite element units, and realizing embedding the skeleton mesh into the finite element mesh; obtaining a quasi-static equation based on the skeleton vertex centroid interpolation weight and the elastic potential energy function fusion of the finite element grid; and obtaining a character animation model based on the skin vertex centroid interpolation weight and the quasi-static equation, and improving the accuracy of the natural deformation of the three-dimensional animation character corresponding to the character animation model under the action of force.

Description

Method, apparatus, computer device and storage medium for creating character animation model
Technical Field
The present application relates to the field of computer technologies, and in particular, to a method and an apparatus for creating a character animation model, a computer device, and a storage medium.
Background
With the development of computer technology, three-dimensional animation design has achieved great economic benefits and social benefits in industry development, and the design of three-dimensional animation characters is an important part in three-dimensional animation design.
In the traditional technology, when a digital character animation model is created, the influence weight of each control node of a digital character in a three-dimensional animation needs to be manually bound, and then the three-dimensional animation corresponding to the digital character model is generated based on each control node and the bound influence weight.
Disclosure of Invention
In view of the above, it is necessary to provide a method, an apparatus, a computer device and a storage medium for creating a character animation model, which can improve the accuracy of generating natural deformation of a three-dimensional animation character corresponding to the character animation model under the action of force.
A method of creating a character animation model, comprising:
acquiring a finite element grid, a skin grid and a skeleton grid, wherein the finite element grid comprises a muscle fiber direction, and the expansion or contraction direction of the finite element grid is determined by the muscle fiber direction when the finite element grid deforms;
obtaining skin vertex centroid interpolation weight according to the position information of the vertices of the skin mesh and the skin vertex finite element units, wherein the skin vertex finite element units are the finite element units containing the vertices of the skin mesh in the finite element mesh, and the skin vertex centroid interpolation weight represents the position incidence relation between the skin vertex finite element units and the vertices of the skin mesh;
obtaining skeleton vertex centroid interpolation weight according to the position information of the vertex of the skeleton mesh and the skeleton vertex finite element unit, wherein the skeleton vertex finite element unit is a finite element unit which contains the vertex of the skeleton mesh in the finite element mesh, and the skeleton vertex centroid interpolation weight represents the position incidence relation between the skeleton vertex finite element unit and the vertex of the skeleton mesh;
fusing to obtain a quasi-static equation based on the skeleton vertex centroid interpolation weight and the elastic potential energy function of the finite element grid, wherein the elastic potential energy function is used for representing the elastic potential energy generated by the finite element grid during deformation, and the quasi-static equation is used for representing the balance degree of the external force and the elastic force applied to the finite element grid;
and obtaining a character animation model based on the skin vertex centroid interpolation weight and the quasi-static equation, wherein the character animation model establishes an incidence relation among a skin mesh, a finite element mesh and a skeleton mesh.
In one embodiment, the quasi-static equation is obtained by fusing the interpolation weight of the bone vertex barycenter and the elastic potential energy function of the finite element mesh, and comprises the following steps:
obtaining a bone driving item according to the fusion of the vertex position information of the bone mesh, the bone vertex centroid interpolation weight, a bone finite element position factor and a bone vertex finite element volume value, wherein the bone finite element position factor is the position information of the vertex of the bone vertex finite element, and the bone driving item is used for representing the position difference between the vertex of the bone mesh and the bone vertex finite element;
and fusing the bone driving item and the elastic potential energy function of the finite element grid to obtain a quasi-static equation.
In one embodiment, the quasi-static equation is obtained from the fusion of the skeletal drive term and the elastic potential energy function of the finite element mesh, and comprises:
acquiring a deformation gradient of the finite element grid, wherein the deformation gradient is used for representing the local deformation degree of the finite element grid;
performing singular value decomposition on the deformation gradient to obtain a singular value corresponding to the deformation gradient;
obtaining a local elastic potential energy function based on singular value fusion;
obtaining an elastic potential energy function of the finite element grid based on local elastic potential energy function fusion;
and fusing the elastic potential energy function based on the skeletal driving item and the finite element grid to obtain a quasi-static equation.
In one embodiment, obtaining a deformation gradient of a finite element mesh comprises:
acquiring a pre-factor, wherein the pre-factor is position information of a vertex of a finite element unit in a finite element grid before initial deformation;
acquiring a post factor, wherein the post factor is position information of vertexes of finite element units in the finite element grid after initial deformation;
and obtaining the deformation gradient of the finite element grid based on the fusion of the pre-factor and the post-factor.
In one embodiment, the quasi-static equation is obtained based on the fusion of the skeletal drive term and the elastic potential energy function of the finite element mesh, and comprises the following steps:
acquiring a gravity driving item, wherein the gravity driving item represents the gravity action of a gravity field on a finite element grid;
and fusing the elastic potential energy functions based on the skeleton driving item, the gravity driving item and the finite element grid to obtain a quasi-static equation.
In one embodiment, the character animation model is obtained based on the skin vertex centroid interpolation weight and the quasi-static equation, and the method comprises the following steps:
obtaining position information of the finite element unit after the vertex of the finite element grid deforms in a stress balance state by solving a quasi-static equation;
and obtaining a role animation model according to the skin vertex centroid interpolation weight and the position information of the deformed vertices of the skin vertex finite element units, wherein the role animation model is used for solving the position information of the vertices of the skin mesh corresponding to the deformation.
In one embodiment, the character animation model includes a skin mesh contained within a finite element mesh and a bone mesh contained within a skin mesh.
An apparatus for creating a character animation model, comprising:
the grid acquisition module is used for acquiring a finite element grid, a skin grid and a skeleton grid, wherein the finite element grid comprises a muscle fiber direction, and the expansion or contraction direction of the finite element grid is determined by the muscle fiber direction when the finite element grid deforms;
the skin vertex centroid interpolation weight generation module is used for obtaining skin vertex centroid interpolation weight according to the position information of the vertices of the skin mesh and the skin vertex finite element units, the skin vertex finite element units are the finite element units containing the vertices of the skin mesh in the finite element mesh, and the skin vertex centroid interpolation weight represents the position incidence relation between the skin vertex finite element units and the vertices of the skin mesh;
the skeleton vertex centroid interpolation weight generation module is used for obtaining skeleton vertex centroid interpolation weight according to the position information of the vertex of the skeleton grid and the skeleton vertex finite element units, the skeleton vertex finite element units are finite element units containing the vertex of the skeleton grid in the finite element grid, and the skeleton vertex centroid interpolation weight represents the position incidence relation between the skeleton vertex finite element units and the vertex of the skeleton grid;
the quasi-static equation generation module is used for fusing to obtain a quasi-static equation based on the skeleton vertex centroid interpolation weight and the elastic potential energy function of the finite element grid, wherein the elastic potential energy function is used for representing the elastic potential energy generated by the finite element grid during deformation, and the quasi-static equation is used for representing the balance degree of the external force and the elastic force applied to the finite element grid;
and the character animation model generation module is used for obtaining a character animation model based on the skin vertex centroid interpolation weight and the quasi-static equation, and the character animation model establishes the incidence relation among the skin mesh, the finite element mesh and the skeleton mesh.
A computer device comprising a memory and a processor, the memory storing a computer program, the processor implementing the following steps when executing the computer program:
acquiring a finite element grid, a skin grid and a skeleton grid, wherein the finite element grid comprises a muscle fiber direction, and the expansion or contraction direction of the finite element grid is determined by the muscle fiber direction when the finite element grid deforms;
obtaining skin vertex centroid interpolation weight according to the position information of the vertices of the skin mesh and the skin vertex finite element units, wherein the skin vertex finite element units are the finite element units containing the vertices of the skin mesh in the finite element mesh, and the skin vertex centroid interpolation weight represents the position incidence relation between the skin vertex finite element units and the vertices of the skin mesh;
obtaining skeleton vertex centroid interpolation weight according to the position information of the vertex of the skeleton mesh and the skeleton vertex finite element unit, wherein the skeleton vertex finite element unit is a finite element unit which contains the vertex of the skeleton mesh in the finite element mesh, and the skeleton vertex centroid interpolation weight represents the position incidence relation between the skeleton vertex finite element unit and the vertex of the skeleton mesh;
fusing to obtain a quasi-static equation based on the skeleton vertex centroid interpolation weight and the elastic potential energy function of the finite element grid, wherein the elastic potential energy function is used for representing the elastic potential energy generated by the finite element grid during deformation, and the quasi-static equation is used for representing the balance degree of the external force and the elastic force applied to the finite element grid;
and obtaining a character animation model based on the skin vertex centroid interpolation weight and the quasi-static equation, wherein the character animation model establishes an incidence relation among a skin mesh, a finite element mesh and a skeleton mesh.
A computer-readable storage medium storing a computer program which, when executed by a processor, performs the steps of:
acquiring a finite element grid, a skin grid and a skeleton grid, wherein the finite element grid comprises a muscle fiber direction, and the expansion or contraction direction of the finite element grid is determined by the muscle fiber direction when the finite element grid deforms;
obtaining skin vertex centroid interpolation weight according to the position information of the vertices of the skin mesh and the skin vertex finite element units, wherein the skin vertex finite element units are the finite element units containing the vertices of the skin mesh in the finite element mesh, and the skin vertex centroid interpolation weight represents the position incidence relation between the skin vertex finite element units and the vertices of the skin mesh;
obtaining skeleton vertex centroid interpolation weight according to the position information of the vertex of the skeleton mesh and the skeleton vertex finite element unit, wherein the skeleton vertex finite element unit is a finite element unit which contains the vertex of the skeleton mesh in the finite element mesh, and the skeleton vertex centroid interpolation weight represents the position incidence relation between the skeleton vertex finite element unit and the vertex of the skeleton mesh;
fusing to obtain a quasi-static equation based on the skeleton vertex centroid interpolation weight and the elastic potential energy function of the finite element grid, wherein the elastic potential energy function is used for representing the elastic potential energy generated by the finite element grid during deformation, and the quasi-static equation is used for representing the balance degree of the external force and the elastic force applied to the finite element grid;
and obtaining a character animation model based on the skin vertex centroid interpolation weight and the quasi-static equation, wherein the character animation model establishes an incidence relation among a skin mesh, a finite element mesh and a skeleton mesh.
According to the method, the device, the computer equipment and the storage medium for creating the character animation model, the finite element mesh, the skin mesh and the skeleton mesh are obtained, wherein the finite element mesh comprises the muscle fiber direction, and the expansion or contraction direction of the finite element mesh is determined by the muscle fiber direction when the finite element mesh is deformed; obtaining skin vertex centroid interpolation weight according to the vertex position information of the skin mesh and the skin vertex finite element unit to realize embedding the skin mesh into the finite element mesh, and obtaining skeleton vertex centroid interpolation weight according to the vertex position information of the skeleton mesh and the skeleton vertex finite element unit to realize embedding the skeleton mesh into the finite element mesh; fusing to obtain a quasi-static equation based on the skeleton vertex centroid interpolation weight and the elastic potential energy function of the finite element grid; and obtaining a character animation model based on the skin vertex centroid interpolation weight and the quasi-static equation, and establishing an incidence relation among the skin mesh, the finite element mesh and the skeleton mesh through the character animation model. Therefore, the skeleton mesh or other external loads of the character animation model drive the movement or deformation of the finite element mesh, then the movement or deformation of the skin mesh is driven by the movement or deformation of the finite element mesh, and when the nonlinear volume deformation of the finite element mesh occurs, the deformation direction and the deformation degree of the skin mesh can be adaptively adjusted through the muscle fiber direction.
Drawings
FIG. 1 is a diagram of an application environment for a method of creating a character animation model in one embodiment;
FIG. 2 is a schematic flow chart diagram illustrating a method for creating a character animation model in one embodiment;
FIG. 3 is a schematic diagram of a process for constructing quasi-static equations in one embodiment;
FIG. 4 is a schematic diagram of a process for constructing a quasi-static equation based on skeletal drive terms in one embodiment;
FIG. 5 is a schematic flow chart illustrating the generation of a deformation gradient in one embodiment;
FIG. 6 is a schematic diagram of a process for constructing quasi-static equations including gravity drives in one embodiment;
FIG. 7 is a schematic flow chart illustrating the generation of a character animation model in one embodiment;
FIG. 8 is a diagram of a finite element mesh of a digitally animated character in one embodiment;
FIG. 9 is a diagram of a finite element mesh with a muscle model embedded therein, according to one embodiment;
FIG. 10 is a schematic diagram of a finite element mesh with a skin mesh embedded therein in one embodiment;
FIG. 11 is an enlarged partial schematic view of a finite element mesh with a skin mesh embedded therein according to one embodiment;
FIG. 12 is a schematic diagram of a finite element mesh with a bone mesh embedded therein in one embodiment;
FIG. 13 is a diagram illustrating the finite element mesh, skin mesh, and bone mesh after bonding in one embodiment;
FIG. 14 is a block diagram of an apparatus for creating a character animation model according to one embodiment;
FIG. 15 is a diagram of an internal structure of a computer device in one embodiment.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.
The method for creating the character animation model provided by the embodiment of the application can be applied to the application environment shown in fig. 1. As shown in fig. 1, the computer device 102 obtains a skin mesh model, a bone mesh model, and a finite element mesh of the digital animation character, the computer device 102 embeds the skin mesh of the digital animation character into the finite element mesh by using a centroid interpolation method, embeds the bone mesh into the finite element mesh, wraps the skin mesh inside the finite element mesh, wraps the bone mesh inside the skin mesh, constructs a quasi-static equation of the character model according to a bone vertex centroid interpolation weight and an elastic potential energy function of the finite element mesh, and obtains the character animation model based on the quasi-static equation and the skin vertex centroid interpolation weight. The computer device 102 may specifically include, but is not limited to, various personal computers, laptops, servers, smartphones, tablets, smart cameras, portable wearable devices, and the like.
In one embodiment, as shown in FIG. 2, a method for creating a character animation model is provided, which is illustrated by way of example as applied to the computer device 102 of FIG. 1, and comprises the steps of:
step S202, acquiring a finite element mesh, a skin mesh and a skeleton mesh, wherein the finite element mesh comprises a muscle fiber direction, and the expansion or contraction direction of the finite element mesh is determined by the muscle fiber direction when the finite element mesh deforms.
The finite element mesh of the animation object is a three-dimensional animation character model for receiving deformation generated by various external forces and the action of skeleton driving force, and is shown in FIG. 8; the skin mesh is a three-dimensional skin model embedded in the finite element mesh of the animation object, and the skin model is a three-dimensional animation model used for displaying or expressing the specific details and the shape of the outer surface of the animation object; the skeleton mesh is used for providing skeleton driving force for deforming the finite element mesh of the animation object to obtain a skeleton model; the finite element mesh, the skin mesh and the skeleton mesh of the animation object can be divided by using methods such as a tetrahedral mesh, a hexahedral mesh or a triangular mesh, so that the finite element mesh, the skin mesh and the skeleton mesh of the animation object are models formed by finite element units, and are not limited herein, the finite element mesh comprises a muscle area, as shown in fig. 9, each vertex of the finite element in the muscle area has muscle fiber direction information, that is, each vertex of the finite element in the muscle area has a direction gradient field which does not cross in space, the deformation of the muscle area has anisotropy, and under the condition of exerting force, the finite element mesh expands along the direction perpendicular to the muscle fiber, that is, when the finite element mesh deforms under the action of external force or automatically deforms through self electric signal excitation, the finite element mesh is enabled to be divided into finite elements, The skin mesh is subjected to natural deformation of expansion and contraction along the direction perpendicular to the muscle fibers, the deformation represents that the shape is changed, the finite element unit is deformed, and represents that the space position, the self shape and the positions of all vertexes of the finite element are changed.
Specifically, the computer device acquires the muscle fiber direction
Figure DEST_PATH_IMAGE002_20A
And two direction vectors perpendicular to each other and to the direction of the fibres
Figure DEST_PATH_IMAGE004_10A
And
Figure DEST_PATH_IMAGE006_10A
combining the three vectors into a rotation matrix, using R to represent the muscle fiber direction of each finite element, and setting the deformation value along the muscle fiber direction to be
Figure DEST_PATH_IMAGE008_12A
Two direction vectors perpendicular to each other and to the direction of the fibres
Figure DEST_PATH_IMAGE010_9A
And
Figure DEST_PATH_IMAGE012_15A
corresponding to a deformation value of
Figure 355052DEST_PATH_IMAGE014
And
Figure DEST_PATH_IMAGE016_7A
using a symmetric array of deformations
Figure DEST_PATH_IMAGE018_8A
To express:
Figure DEST_PATH_IMAGE020_8A
equation 1
Wherein
Figure DEST_PATH_IMAGE022_8A
To be composed of
Figure DEST_PATH_IMAGE024_8A
Is a diagonal matrix of diagonal elements, from which the deformation expression of the initial state is obtained as:
Figure DEST_PATH_IMAGE026_8A
equation 2
Wherein the content of the first and second substances,
Figure DEST_PATH_IMAGE028_8A
an initial state when the anisotropy of the muscle deformation is not considered for the finite element mesh;
Figure DEST_PATH_IMAGE030_8A
an initial state when anisotropy of muscle deformation is taken into account for the finite element mesh; then will be
Figure DEST_PATH_IMAGE031AAAA
And adding the obtained data into a subsequent finite element grid elastic potential energy function for calculation to obtain a quasi-static equation, and calculating the force and the anisotropic deformation of the muscle.
And step S204, obtaining skin vertex centroid interpolation weight according to the position information of the vertex of the skin mesh and the skin vertex finite element unit, wherein the skin vertex finite element unit is a finite element unit which contains the vertex of the skin mesh in the finite element mesh, and the skin vertex centroid interpolation weight represents the position incidence relation between the skin vertex finite element unit and the vertex of the skin mesh.
The skin vertex finite element unit is a finite element unit containing the vertices of the skin mesh, and the position transformation interpolation weight represents the position incidence relation between the skin vertex finite element unit and the vertices of the skin mesh.
Specifically, the computer device adjusts the skin mesh to a suitable position in the finite element mesh, and then obtains the vertices of the skin meshPThe position coordinates and the finite element mesh of (1) include the skin vertexPTetrahedral unit of
Figure DEST_PATH_IMAGE033_7A
Each vertexP 0 ,P 1 ,P 2 ,P 3 The position coordinates of (2) then obtain pointsPCentroid interpolation weights for four tetrahedrons
Figure DEST_PATH_IMAGE035_7A
The centroid interpolation weight satisfies the following formula 3:
Figure DEST_PATH_IMAGE037_7A
equation 3
Wherein the content of the first and second substances,
Figure DEST_PATH_IMAGE039_7A
，
Figure DEST_PATH_IMAGE041_8A
，
Figure DEST_PATH_IMAGE043_8A
，
Figure DEST_PATH_IMAGE045_8A
，Vrepresenting a volume of tetrahedrons consisting of four points, e.g.
Figure DEST_PATH_IMAGE047_8A
Is represented by
Figure DEST_PATH_IMAGE049_7A
The volume of a tetrahedron formed by four points,
Figure DEST_PATH_IMAGE051_7A
satisfy the requirement of
Figure DEST_PATH_IMAGE053_7A
When the finite element grid is deformed, the tetrahedral unit is arranged
Figure DEST_PATH_IMAGE055_7A
The corresponding vertex coordinates after four deformations are
Figure DEST_PATH_IMAGE057_7A
Then, the coordinates of the new skin vertex after interpolation after deformation along with the finite element unit of the finite element mesh can be calculated
Figure DEST_PATH_IMAGE059_7A
Comprises the following steps:
Figure DEST_PATH_IMAGE061_7A
embedding the skin mesh into the initial shape of the finite element mesh by the skin vertex barycenter interpolation weight, and establishing the tetrahedral unit of the finite element mesh including the skin vertex
Figure DEST_PATH_IMAGE063_7A
Mesh vertex with skinPThe position association relationship between them.
And step S206, obtaining skeleton vertex centroid interpolation weight according to the position information of the vertex of the skeleton mesh and the skeleton vertex finite element, wherein the skeleton vertex finite element is a finite element containing the vertex of the skeleton mesh in the finite element mesh, and the skeleton vertex centroid interpolation weight represents the position incidence relation between the skeleton vertex finite element and the vertex of the skeleton mesh.
The vertex of the skeleton mesh is each vertex of the finite element units in the skeleton mesh, taking a tetrahedral unit as an example, each finite element unit on the skeleton mesh has four vertices, the skeleton vertex centroid interpolation weight is used for describing the position transformation interpolation weight of the vertex of the skeleton mesh relative to each vertex of the finite element units of the skeleton vertex in the space, the skeleton vertex finite element unit is a tetrahedral unit which contains the vertex of the skeleton mesh on the finite element mesh of the animation object, and the skeleton vertex centroid interpolation weight represents the position association relationship between the skeleton vertex finite element unit and the vertex of the skeleton mesh.
Specifically, the computer device adjusts the skeleton mesh to a suitable position inside the skin mesh, and then obtains the vertices of the skeleton meshPThe position coordinates of (a) and tetrahedral elements of the finite element mesh including the bone vertices
Figure DEST_PATH_IMAGE065_7A
Each vertexP 0 ,P 1 ,P 2 ,P 3 The position coordinates of (2) then obtain pointsPCentroid interpolation weights for four tetrahedrons
Figure DEST_PATH_IMAGE067_7A
And the centroid interpolation weight satisfies:
Figure DEST_PATH_IMAGE069_7A
equation 4
Wherein, the first and the second end of the pipe are connected with each other,
Figure DEST_PATH_IMAGE070_5A
，
Figure DEST_PATH_IMAGE071_11A
，
Figure DEST_PATH_IMAGE072_7A
，
Figure DEST_PATH_IMAGE073_8A
，Vrepresenting four sides consisting of four pointsVolume of body, e.g.
Figure DEST_PATH_IMAGE075_7A
Is represented by
Figure 991831DEST_PATH_IMAGE077
The volume of a tetrahedron formed by four points,
Figure 727706DEST_PATH_IMAGE079
satisfy the requirements of
Figure DEST_PATH_IMAGE081_9A
When the finite element grid is deformed, the tetrahedral unit is arranged
Figure DEST_PATH_IMAGE083_8A
The corresponding vertex coordinates after four deformations are
Figure DEST_PATH_IMAGE085_7A
Then, the coordinates of the new skeleton vertex after interpolation deformed with the finite element unit of the finite element mesh can be calculated
Figure DEST_PATH_IMAGE087_7A
Comprises the following steps:
Figure DEST_PATH_IMAGE089_7A
embedding the skin mesh into the initial shape of the finite element mesh by the weight of the barycenter interpolation of the bone vertex, and establishing the tetrahedral unit of the finite element mesh including the bone vertex
Figure DEST_PATH_IMAGE090_9A
And skeleton mesh verticesPThe position association relationship between them.
And S208, fusing to obtain a quasi-static equation based on the skeleton vertex centroid interpolation weight and the elastic potential energy function of the finite element grid, wherein the elastic potential energy function is used for representing the elastic potential energy generated by the finite element grid during deformation, and the quasi-static equation is used for representing the balance degree of the external force and the elastic force applied to the finite element grid.
Wherein, the elastic potential energy function of the finite element grid is obtained by fusing the elastic potential energy of the finite element units in the discrete space, and for any finite element on the discrete grid
Figure DEST_PATH_IMAGE091_11A
The corresponding deformation gradient can be calculated
Figure DEST_PATH_IMAGE093_7A
Finite element volume in initial shape
Figure DEST_PATH_IMAGE095_7A
And area normal of four faces of tetrahedron
Figure DEST_PATH_IMAGE097_7A
The elastic potential energy of the finite element unit caused by deformation can be calculated
Figure DEST_PATH_IMAGE099_7A
Stress tensor of finite element unit body
Figure DEST_PATH_IMAGE101_7A
Elastic force generated by four vertexes of unit body
Figure DEST_PATH_IMAGE103_7A
Wherein, in the step (A),
Figure DEST_PATH_IMAGE105_15A
is a function of the elastic potential energy at a point on the finite element mesh.
Setting the number of the vertex points of the finite element grid as N and the number of the finite element units as
Figure DEST_PATH_IMAGE107_17A
Combining the positions of all the vertexes into one
Figure DEST_PATH_IMAGE109_17A
Vector of (2), for the initial shape noted
Figure DEST_PATH_IMAGE111_14A
The deformation shape is marked as
Figure DEST_PATH_IMAGE113_8A
. Defining a finite element selection matrix of
Figure DEST_PATH_IMAGE115_11A
For extraction of
Figure DEST_PATH_IMAGE116_10A
And
Figure DEST_PATH_IMAGE117_13A
corresponding to e-th finite element unit
Figure DEST_PATH_IMAGE119_12A
The sub-vectors of (a):
Figure 140320DEST_PATH_IMAGE121
，
Figure 12461DEST_PATH_IMAGE123
defining an assembly matrix
Figure 740246DEST_PATH_IMAGE125
For forming vertices of finite element elements
Figure DEST_PATH_IMAGE119_13A
Vector transformation into recomposition
Figure DEST_PATH_IMAGE109_18A
Vector quantity:
Figure DEST_PATH_IMAGE127_9A
，
Figure DEST_PATH_IMAGE129_7A
and further obtaining the elastic potential energy of the whole finite element grid:
Figure DEST_PATH_IMAGE131_7A
and obtaining the elastic force on the vertex of the finite element mesh:
Figure DEST_PATH_IMAGE133_7A
obtaining a hessian matrix of the tetrahedral mesh:
Figure DEST_PATH_IMAGE135_7A
。
when an external load is applied to an elastic object, the elastic object can deform after a given boundary condition (a plurality of fixed parts) is given, generally, the deformation is a dynamic process, and under the stable external load and the boundary condition, because of the existence of damping force, the dynamic deformation can become a static deformation with balanced stress. When the damping of a mechanical system is large, the deformation process often occurs instantly, a force balance state is reached within a short time, the process of reaching the balance state within a short enough time (far lower than the time step of simulation) is called as a quasi-static process (quasi-static), a quasi-static equation is used for representing the balance degree of external force and elastic force applied to a finite element grid, and the static balance state is often directly solved when the quasi-static process is solved. The elastic body is subjected to elastic force and gravity in the quasi-static process, the gravity accelerometer is g, the quasi-static process is essentially in a state of solving equilibrium, and the equilibrium is in a state with the lowest potential energy, so that the problem of optimizing the mechanical energy of the system in the quasi-static process can be converted into the following steps:
Figure DEST_PATH_IMAGE137_7A
equation 5
Wherein the content of the first and second substances,
Figure DEST_PATH_IMAGE139_7A
is the intensity of the driving energy of the bone,
Figure DEST_PATH_IMAGE141_7A
for the position of each vertex of the skeleton mesh,
Figure DEST_PATH_IMAGE143_7A
the skeleton driving item is obtained by fusing the skeleton vertex barycenter interpolation weight and the volume of the finite element unit of the finite element grid, is used for driving the finite element grid of the skeleton, and when the finite element grid is stressed to be balanced by external force load and self elastic force, the position coordinate of each vertex at the moment is solved
Figure DEST_PATH_IMAGE145_13A
Namely, coordinates of each vertex after the finite element mesh is deformed; newton iterations can be used to solve equation 5 above, assuming the initial assumption of equation solution is
Figure DEST_PATH_IMAGE147_13A
The iterative process is as follows:
Figure DEST_PATH_IMAGE149_13A
equation 6
Figure DEST_PATH_IMAGE151_7A
Equation 7
Figure DEST_PATH_IMAGE153_11A
Equation 8
Wherein, the SDP algorithm (semi-definite programming algorithm) is responsible for projecting the non-definite matrix into a definite matrix, thereby ensuring the stability of the Newton iterative algorithm,
Figure DEST_PATH_IMAGE155_7A
is the step size of the backward linear Search (backing Line Search).
Step S210, a character animation model is obtained based on the skin vertex centroid interpolation weight and the quasi-static equation, and the character animation model establishes the incidence relation among the skin mesh, the finite element mesh and the skeleton mesh.
The output of the character animation model is the position coordinates of each vertex on the skin mesh embedded in the finite element mesh after deformation.
Specifically, after the computer device solves the position information of each vertex of the deformed finite element mesh through the steps, the deformed position information corresponding to each vertex of the skin mesh is obtained according to the position association relationship (namely the skin vertex centroid interpolation weight) between the position information of each vertex of the finite element mesh and the position of the finite element mesh and the skin mesh, and then the color animation after deformation is obtained.
According to the method, the device, the computer equipment and the storage medium for creating the character animation model, the finite element mesh, the skin mesh and the skeleton mesh are obtained, wherein the finite element mesh comprises the muscle fiber direction, and the expansion or contraction direction of the finite element mesh is determined by the muscle fiber direction when the finite element mesh is deformed; then, obtaining skin vertex centroid interpolation weight according to the vertex position information of the skin mesh and the skin vertex finite element unit, realizing that the skin mesh is embedded into the finite element mesh, as shown in fig. 10 and fig. 11, obtaining bone vertex centroid interpolation weight according to the vertex position information of the bone mesh and the bone vertex finite element unit, realizing that the bone mesh is embedded into the finite element mesh, as shown in fig. 12; fusing to obtain a quasi-static equation based on the skeleton vertex centroid interpolation weight and the elastic potential energy function of the finite element grid; the character animation model is obtained based on the skin vertex centroid interpolation weight and the quasi-static equation, and therefore the incidence relation among the skin mesh, the finite element mesh and the skeleton mesh is established through the character animation model, as shown in fig. 13. Like this, the motion of the skeleton net of role animation model or other external force load drive finite element net or take place deformation, the motion or the deformation that are driving the skin net by the motion or the deformation of finite element net again, and when the nonlinear volume deformation takes place in the finite element net, the deformation direction and the deformation degree of skin net can carry out self-adaptation ground adjustment through muscle fibre direction, in addition, muscle is under the condition that does not have the external force load effect, also can independently take place deformation through self electric signal excitation, also can order about the finite element in the finite element net and take place deformation along muscle fibre direction, make it produce natural deformation, improve the accuracy that three-dimensional animation role that role animation model corresponds produced natural deformation under the effect of force.
In one embodiment, as shown in fig. 3, the quasi-static equation is obtained by fusing the interpolation weights of the bone vertex centroids and the elastic potential energy function of the finite element mesh, and comprises the following steps:
step S302, a bone driving item is obtained according to the top point position information of the bone mesh, the bone top point centroid interpolation weight, the bone finite element position factor and the volume value fusion of the bone top point finite element units, wherein the bone finite element position factor is the position information of the top points of the bone top point finite element units, and the bone driving item is used for representing the position difference between the top points of the bone mesh and the bone top point finite element units.
For example, let the vertex of the bone be
Figure DEST_PATH_IMAGE157_7A
The number of vertexes is
Figure DEST_PATH_IMAGE159_7A
Let the finite element in which each vertex is located be
Figure DEST_PATH_IMAGE161_11A
Four vertices of the finite element are
Figure DEST_PATH_IMAGE163_7A
The corresponding finite element mesh has a finite element volume of
Figure DEST_PATH_IMAGE165_8A
Corresponding barycentric interpolation coordinates of
Figure DEST_PATH_IMAGE167_7A
Defining the skeletal drive term as:
Figure DEST_PATH_IMAGE169_7A
equation 9
From equation 9, the skeletal driving term is related to
Figure 58357DEST_PATH_IMAGE171
The hessian matrix is constant and positive, and the bone driving term formula 9 is added into the quasi-static equation, so that unstable non-positive behavior cannot be generated.
And step S304, obtaining a quasi-static equation according to the fusion of the bone driving item and the elastic potential energy function of the finite element grid.
Specifically, the computer device obtains a bone driving item based on the steps, and fuses the bone driving item and the elastic potential energy function of the finite element grid to obtain a quasi-static equation.
In the embodiment, a bone driving item is obtained by fusing the vertex position information of the bone mesh, the bone vertex centroid interpolation weight, the bone finite element position factor and the finite element volume value of the finite element mesh corresponding to the vertex of the bone mesh, and a quasi-static equation is obtained by fusing the bone driving item and the elastic potential energy function of the finite element mesh, so that the bone driving force can be included in the process of solving the quasi-static equation, and the function of driving the finite element mesh to move by the bone is realized.
In one embodiment, as shown in FIG. 4, the quasi-static equation is obtained from the fusion of the skeletal drive term and the elastic potential energy function of the finite element mesh, and comprises:
step S402, obtaining the deformation gradient of the finite element grid, wherein the deformation gradient is used for representing the local deformation degree of the finite element grid.
Wherein, the deformation gradient is determined by the position of the vertex in the elastomer after deformation and the position of the vertex in the elastomer before deformation after deformation (the finite element mesh in the scheme), for example: the elastic body occupies a continuous space in three-dimensional space, and the elastic body occupies the space in the initial shape
Figure 264210DEST_PATH_IMAGE173
Let the position of any point therein be
Figure 256437DEST_PATH_IMAGE175
When the elastic body is deformed relative to the initial shape, the deformed elastic body is setThe position of each point in the body is
Figure 155123DEST_PATH_IMAGE177
For any elastic deformation, a continuous two-way mapping from the initial shape to the deformed shape is defined:
Figure DEST_PATH_IMAGE179_5A
wherein
Figure 68852DEST_PATH_IMAGE181
Sufficiently describing any one of continuous elastic deformation, mapping function
Figure 547238DEST_PATH_IMAGE182
Carrying out Taylor expansion:
Figure DEST_PATH_IMAGE184_17A
to obtain
Figure 128392DEST_PATH_IMAGE186
Let us order
Figure 932400DEST_PATH_IMAGE188
Is one
Figure 130163DEST_PATH_IMAGE190
Matrix, Polar Decomposition (Polar Decomposition) is performed on it:
Figure DEST_PATH_IMAGE192_6A
whereinRIs one
Figure 615503DEST_PATH_IMAGE193
S is a matrix characterizing shear strain
Figure 409470DEST_PATH_IMAGE194
Symmetric matrix of (2), derivative matrix ofFReferred to as deformation gradient.
Specifically, when the finite element mesh deforms, the computer device randomly gives an initial value of a deformation gradient, and solves the quasi-static equation in the step in a continuous iteration mode until an iteration stop condition is met.
And S404, performing singular value decomposition on the deformation gradient to obtain a singular value corresponding to the deformation gradient.
Specifically, the deformation gradient of the finite element is set as
Figure 384379DEST_PATH_IMAGE196
Computer device to deformation gradient
Figure 69439DEST_PATH_IMAGE197
Singular value decomposition is performed so that
Figure 420785DEST_PATH_IMAGE199
To obtain three singular values
Figure 242111DEST_PATH_IMAGE201
Respectively expressing the pull-up shrinkage degree of the unit body deformation in the directions of three deformation main axes.
And step S406, obtaining a local elastic potential energy function based on singular value fusion.
Specifically, the computer device obtains three feature quantities according to the singular values:
Figure 653501DEST_PATH_IMAGE203
，
Figure DEST_PATH_IMAGE205_6A
，
Figure DEST_PATH_IMAGE207_7A
and then, fusing according to the characteristic quantity to obtain a local elastic potential energy function:
Figure DEST_PATH_IMAGE209_7A
equation 10
Wherein
Figure DEST_PATH_IMAGE211_17A
，
Figure 311009DEST_PATH_IMAGE213
The Lame coefficient is used for describing the rigidity and volume retention capability of the finite element grid.
And step S408, fusing to obtain an elastic potential energy function of the finite element grid based on the local elastic potential energy function.
Specifically, the computer equipment corresponds the local elastic potential energy function of each finite element unit
Figure DEST_PATH_IMAGE215_5A
Fusing to obtain the elastic potential energy function of the finite element grid
Figure DEST_PATH_IMAGE217_7A
Wherein, in the step (A),
Figure DEST_PATH_IMAGE219_7A
the number of finite element elements in the finite element mesh.
And S410, fusing the elastic potential energy function based on the skeletal driving item and the finite element grid to obtain a quasi-static equation.
Specifically, the computer device applies the elastic potential energy function of the finite element mesh
Figure DEST_PATH_IMAGE221_7A
And the skeletal driving item
Figure 479429DEST_PATH_IMAGE223
And performing fusion to obtain a quasi-static equation.
In the embodiment, the deformation gradient of the finite element grid is obtained, singular value decomposition is performed on the deformation gradient to obtain singular values corresponding to the deformation gradient, a local elastic potential energy function is obtained based on singular value fusion, and then a quasi-static equation is obtained based on fusion of the bone driving item and the elastic potential energy function of the finite element grid, so that the bone driving force can be included in the process of solving the quasi-static equation to realize the function of the bone driving the finite element grid to move, and meanwhile, the elastic potential energy function of the finite element grid is obtained by fusion of the local elastic potential energy functions corresponding to all finite element units in the finite element grid, so that the elastic potential energy function of the finite element grid can reflect the size of the elastic potential energy generated by each finite element unit in the finite element grid when the finite element grid is deformed.
In one embodiment, as shown in FIG. 5, obtaining a deformation gradient of a finite element mesh comprises:
step S502, acquiring a pre-set factor, wherein the pre-set factor is position information of the vertex of the finite element unit in the finite element mesh before initial deformation.
Step S504, a post-factor is obtained, wherein the post-factor is position information of the vertex of the finite element unit in the finite element grid after the initial deformation.
The position information after the initial deformation may be determined in a randomly given manner, may also be determined according to an empirical value, and may also be determined by iteration according to an intelligent optimization algorithm, such as a particle swarm algorithm, a genetic algorithm, a swarm optimization algorithm, and the like, which is not limited specifically here.
And S506, fusing the pre-factor and the post-factor to obtain the deformation gradient of the finite element grid.
Specifically, the computer equipment acquires four vertex positions of the finite element unit in the finite element mesh in the initial state
Figure DEST_PATH_IMAGE225_5A
The four vertex positions in the corresponding deformation state are
Figure 358523DEST_PATH_IMAGE227
Linear finite elements are represented in a finite element with the deformation gradient constant, i.e. with
Figure 675235DEST_PATH_IMAGE229
，
Figure 69307DEST_PATH_IMAGE231
，
Figure 762457DEST_PATH_IMAGE233
，
Figure 558375DEST_PATH_IMAGE235
Simplifying the shift term to obtain the deformation gradient
Figure DEST_PATH_IMAGE237_5A
The equation of (c):
Figure DEST_PATH_IMAGE239_7A
equation 11
Figure 721021DEST_PATH_IMAGE241
Equation 12
Figure 71231DEST_PATH_IMAGE243
Equation 13
Obtaining the deformation gradient in the finite element unit according to the formula 11, the formula 12 and the formula 13
Figure 302492DEST_PATH_IMAGE245
。
In the embodiment, the deformation gradient of the finite element unit is obtained by acquiring the position information of each vertex before the deformation of the finite element unit and the position information of each vertex after the deformation of the finite element unit, and the deformation gradient of the whole finite element unit can be accurately determined by determining the deformation gradient of the position information of each vertex of the finite element unit for the linear finite element.
In one embodiment, as shown in fig. 6, the quasi-static equation is obtained based on the fusion of the skeletal drive term and the elastic potential energy function of the finite element mesh, and comprises:
step S602, a gravity driving item is obtained, and the gravity driving item represents the gravity action of the gravity field on the finite element grid.
And step S604, fusing the elastic potential energy functions of the bone driving item, the gravity driving item and the finite element grid to obtain a quasi-static equation.
In this embodiment, the computer device obtains the gravity-driven item
Figure 952917DEST_PATH_IMAGE247
Wherein
Figure 877010DEST_PATH_IMAGE249
Is a gravity force borne by the vertex
Figure 245675DEST_PATH_IMAGE251
Of
Figure 280627DEST_PATH_IMAGE253
The vector is fused with the elastic potential energy function of the finite element grid according to the bone driving item, the gravity driving item to obtain a quasi-static equation, and the quasi-static equation is obtained:
Figure 785557DEST_PATH_IMAGE255
equation 14
Wherein the gravity drives the item
Figure 880552DEST_PATH_IMAGE257
The gravity action of the gravity field on the finite element grid is expressed, so that the skin of the character model presents natural sagging feeling under the action of the normal gravity field, and the natural visual presentation of the deformation of the skin of the animated character model is improved.
In one embodiment, as shown in fig. 7, the character animation model is obtained based on the skin vertex centroid interpolation weight and the quasi-static equation, and the method comprises the following steps:
step S702, obtaining the position information of the finite element unit after the vertex of the finite element grid deforms in the stress balance state by solving the quasi-static equation.
Step S704, according to the skin vertex centroid interpolation weight and the position information of the deformed vertices of the skin vertex finite element units, a role animation model is obtained, and the role animation model is used for solving the position information of the vertices of the skin mesh after corresponding deformation.
In this embodiment, the computer device obtains the deformed mesh vertexes and the skin mesh vertexes by solving the quasi-static equation in the above steps
Figure 267671DEST_PATH_IMAGE259
Vertex position information of finite element elements of corresponding finite element mesh
Figure 840735DEST_PATH_IMAGE261
Interpolation of weight by skin vertex centroid
Figure 465752DEST_PATH_IMAGE263
To obtain character animation model, namely, skin mesh vertex
Figure DEST_PATH_IMAGE265_5A
Deformed position information
Figure 669331DEST_PATH_IMAGE267
：
Figure 744079DEST_PATH_IMAGE269
Equation 15
Obtaining the skin mesh vertices by equation 15 above
Figure 386413DEST_PATH_IMAGE271
And similarly, obtaining new position information of all the vertexes of the finite element grid after deformation by solving a quasi-static equation, obtaining new position coordinates of all the vertexes of the skin grid after deformation according to the new position information of all the vertexes of the finite element grid after deformation and the skin vertex centroid interpolation weight, and further obtaining position information of all parts of the whole deformed skin grid, so that the reliability of driving the character skin grid to move by the deformation of the finite element grid is improved.
In one embodiment, in the character animation model, the skin mesh is contained inside the finite element mesh and the bone mesh is contained inside the skin mesh.
The application also provides an application scenario, wherein the application scenario applies the method for creating the character animation model, and the method is applied to a scenario for creating a three-dimensional animation character model, and specifically, the application of the method for creating the three-dimensional animation character model in the application scenario is as follows:
the method comprises the steps that computer equipment acquires a finite element mesh, a skin mesh and a skeleton mesh, wherein the finite element mesh comprises a muscle fiber direction, and the expansion or contraction direction of the finite element mesh is determined by the muscle fiber direction when the finite element mesh is deformed; computer equipment obtains muscle fibre direction
Figure 865936DEST_PATH_IMAGE273
And two direction vectors perpendicular to each other and to the direction of the fibres
Figure 302733DEST_PATH_IMAGE275
And
Figure 867707DEST_PATH_IMAGE277
combining the three vectors into a rotation matrix
Figure 782573DEST_PATH_IMAGE279
The muscle fiber direction of each finite element is represented by R, and the deformation value along the muscle fiber direction is set to
Figure 382182DEST_PATH_IMAGE281
Two direction vectors perpendicular to each other and to the direction of the fibres
Figure 989880DEST_PATH_IMAGE283
And
Figure 42150DEST_PATH_IMAGE285
corresponding to a deformation value of
Figure 760707DEST_PATH_IMAGE287
And
Figure 214822DEST_PATH_IMAGE289
to obtain a symmetric array
Figure 993423DEST_PATH_IMAGE291
(ii) a Wherein
Figure 532988DEST_PATH_IMAGE293
To be composed of
Figure 55237DEST_PATH_IMAGE295
Is a diagonal matrix of diagonal elements, thereby obtaining a deformation expression of an initial state:
Figure 363858DEST_PATH_IMAGE297
wherein, in the step (A),
Figure 773412DEST_PATH_IMAGE299
an initial state when anisotropy of muscle deformation is not considered for the finite element mesh;
Figure 534695DEST_PATH_IMAGE301
an initial state when anisotropy of muscle deformation is taken into account for the finite element mesh; then will be
Figure 860634DEST_PATH_IMAGE303
Adding the obtained data into a subsequent finite element grid elastic potential energy function for calculation to obtain a quasi-static equation, and calculating the force application and the anisotropic deformation of the muscle; the computer equipment adjusts the skeleton mesh to the proper position in the skin mesh and then obtains the top point of the skeleton meshPPosition coordinates of the skeleton and tetrahedral elements of the finite element mesh including the vertices of the skeleton
Figure 23762DEST_PATH_IMAGE305
Each vertexP 0 ,P 1 ,P 2 ,P 3 The position coordinates of (2) then obtain pointsPCentroid interpolation weights for four tetrahedrons
Figure 144165DEST_PATH_IMAGE307
The computer device being based on the vertices of the skeleton
Figure 658323DEST_PATH_IMAGE309
The number of vertexes is
Figure 522373DEST_PATH_IMAGE311
The finite element unit where the vertex is located is
Figure 540008DEST_PATH_IMAGE313
Four vertices of finite element
Figure 96891DEST_PATH_IMAGE315
Volume of finite element of corresponding finite element mesh
Figure 832766DEST_PATH_IMAGE317
Corresponding barycentric interpolation coordinates
Figure 234929DEST_PATH_IMAGE319
And obtaining the bone driving term, as shown in formula 9, the computer device adjusts the skin mesh to a proper position in the finite element mesh, and then obtains the top point of the skin mesh
Figure 372649DEST_PATH_IMAGE321
The position coordinates of the skin and the tetrahedral elements of the finite element mesh including the skin vertices
Figure 100433DEST_PATH_IMAGE323
Each vertex
Figure 58025DEST_PATH_IMAGE325
The position coordinates of (2) then obtain points
Figure 529458DEST_PATH_IMAGE326
Skin vertex centroid interpolation weights for four tetrahedrons
Figure 521685DEST_PATH_IMAGE328
(ii) a Fusing to obtain a quasi-static equation based on the skeleton vertex centroid interpolation weight and the elastic potential energy function of the finite element grid; obtaining a character animation model based on the skin vertex barycenter interpolation weight and the quasi-static equation, thereby establishing the incidence relation among the skin mesh, the finite element mesh and the skeleton mesh through the character animation model, and when the finite element mesh is usedWhen deformation occurs, the computer device gives an initial deformation value, an initial deformation gradient is obtained from the initial deformation value, then the initial deformation gradient participates in the solving process of the quasi-static equation, residual errors generated in the iteration process are fed back through continuous iteration to obtain a target value of the deformation gradient, further coordinates of all vertexes of the finite element grid after deformation when the finite element grid is in stress balance are obtained, then the coordinates of all vertexes of the finite element grid after deformation when the finite element grid is in stress balance and the interpolation weight of the skin vertex centroid are calculated according to a formula 15 to obtain corresponding deformation on the skin grid, and the establishment of the three-dimensional digital character animation model is achieved.
The computer obtains the force value of each skeleton gesture and muscle, determines the deformation of only one finite element grid, adds the inertia motion of fat fascia under the existing frame in order to make the deformation of skin have the sliding sense between general fat motion or skin fascia, uses the spring vibrator to realize the effect, the input of the algorithm is the key frame and previous frames obtained by the current quasi-static solver, the used continuous key frame number is different according to the different spring vibrator solvers, takes the display Euler integrator as an example, sets the current frame as the k-th frame, and takes the quasi-static solution result of two continuous frames as
Figure 685950DEST_PATH_IMAGE330
Set previous dither frame
Figure 393487DEST_PATH_IMAGE332
Setting the hardness of the spring vibrator as k and the damping coefficient of the spring vibrator as d, and then using display Euler iterative calculation
Figure 403031DEST_PATH_IMAGE334
：
Figure 249765DEST_PATH_IMAGE336
Equation 16
Figure 319352DEST_PATH_IMAGE338
Equation 17
Figure 720377DEST_PATH_IMAGE340
Equation 18
Wherein
Figure 533612DEST_PATH_IMAGE342
The shaking strength of each vertex of the character skin mesh is obtained, so that the character fat movement or the sliding feeling among skin fascias in the three-dimensional animation is realized, the movement is more natural and vivid, and the visual effect is enhanced.
In the method for creating the character animation model, bones are used as collision bodies, muscles are used as elastic bodies, when a finite element grid deforms, the deformation of the finite element grid is pulled up and contracted along the direction of muscle fibers, and the finite element grid expands and contracts along two mutually perpendicular vector directions which are perpendicular to the direction of the muscle fibers, so that the influence weights of experienced personnel on each control node of a digital character in the three-dimensional animation are not required to be bound, and the volume deformation of the digital character in the motion process is nonlinear, so that when a manual weight binding mode is adopted, accurate configuration is difficult to perform in advance, the generated three-dimensional animation is easy to generate unnatural deformation, and the deformation degree of each part can be adjusted in a self-adaptive manner without manual binding, the accuracy of the animation character corresponding to the three-dimensional animation character model presenting natural deformation is improved.
It should be understood that, although the steps in the flowcharts related to the embodiments as described above are sequentially displayed as indicated by arrows, the steps are not necessarily performed sequentially as indicated by the arrows. The steps are not performed in the exact order shown and described, and may be performed in other orders, unless explicitly stated otherwise. Moreover, at least a part of the steps in the flowcharts related to the embodiments described above may include multiple steps or multiple stages, which are not necessarily performed at the same time, but may be performed at different times, and the execution order of the steps or stages is not necessarily sequential, but may be rotated or alternated with other steps or at least a part of the steps or stages in other steps.
In one embodiment, as shown in fig. 14, there is provided an apparatus for creating a character animation model, which may be a part of a computer device using a software module or a hardware module, or a combination of the two, the apparatus specifically comprising: a mesh acquisition module 1402, a skin vertex centroid interpolation weight generation module 1404, a bone vertex centroid interpolation weight generation module 1406, a quasi-static equation generation module 1408, and a character animation model generation module 1410, wherein:
a mesh acquisition module 1402, configured to acquire a finite element mesh, a skin mesh, and a bone mesh, where the finite element mesh includes a muscle fiber direction, and an expansion or contraction direction of the finite element mesh is determined by the muscle fiber direction when the finite element mesh deforms;
the skin vertex centroid interpolation weight generation module 1404 is used for obtaining skin vertex centroid interpolation weights according to the position information of the vertices of the skin mesh and the skin vertex finite element units, wherein the skin vertex finite element units are the finite element units including the vertices of the skin mesh in the finite element mesh, and the skin vertex centroid interpolation weights represent the position incidence relation between the skin vertex finite element units and the vertices of the skin mesh;
the skeleton vertex centroid interpolation weight generation module 1406 is configured to obtain a skeleton vertex centroid interpolation weight according to the position information of the vertex of the skeleton mesh and the skeleton vertex finite element units, where the skeleton vertex finite element units are finite element units including vertices of the skeleton mesh in the finite element mesh, and the skeleton vertex centroid interpolation weight represents a position association relationship between the skeleton vertex finite element units and the vertices of the skeleton mesh;
the quasi-static equation generation module 1408 is configured to fuse the skeleton vertex centroid interpolation weight and the elastic potential energy function of the finite element mesh to obtain a quasi-static equation, where the elastic potential energy function is used to represent the elastic potential energy generated by the finite element mesh during deformation, and the quasi-static equation is used to represent the degree of balance between the external force applied to the finite element mesh and the elastic force;
and the role animation model generation module 1410 is used for obtaining a role animation model based on the skin vertex centroid interpolation weight and the quasi-static equation, wherein the role animation model establishes an incidence relation among a skin mesh, a finite element mesh and a skeleton mesh.
In one embodiment, the quasi-static equation generation module 1408 is further configured to obtain a bone driving term according to the vertex position information of the bone mesh, the bone vertex centroid interpolation weight, the bone finite element position factor, and the volume value fusion of the bone vertex finite element, where the bone finite element position factor is the position information of the vertices of the bone vertex finite element, and the bone driving term is used to represent the position difference between the vertices of the bone mesh and the bone vertex finite element; and fusing the bone driving item and the elastic potential energy function of the finite element grid to obtain a quasi-static equation.
In one embodiment, the quasi-static equation generation module 1408 is further configured to obtain a deformation gradient of the finite element mesh, where the deformation gradient is used to characterize a local deformation degree of the finite element mesh; performing singular value decomposition on the deformation gradient to obtain a singular value corresponding to the deformation gradient; obtaining a local elastic potential energy function based on singular value fusion; obtaining an elastic potential energy function of the finite element grid based on local elastic potential energy function fusion; and fusing the elastic potential energy function based on the skeletal driving item and the finite element grid to obtain a quasi-static equation.
In one embodiment, the quasi-static equation generation module 1408 is further configured to obtain a pre-factor, where the pre-factor is location information of a vertex of the finite element in the finite element mesh before the initial deformation; acquiring a post factor, wherein the post factor is position information of vertexes of finite element units in the finite element mesh after initial deformation, and the position information after the initial deformation is determined by random giving; and obtaining the deformation gradient of the finite element grid based on the fusion of the pre-factor and the post-factor.
In one embodiment, the quasi-static equation generation module 1408 is further configured to obtain a gravity-driven term, where the gravity-driven term represents a gravitational effect exerted by the gravitational field on the finite element mesh; and fusing the elastic potential energy functions based on the skeleton driving item, the gravity driving item and the finite element grid to obtain a quasi-static equation.
In one embodiment, the character animation model generation module 1410 is further configured to obtain position information of the finite element mesh after the vertex of the finite element unit deforms in the stress balance state by solving a quasi-static equation; and obtaining a role animation model according to the skin vertex centroid interpolation weight and the position information of the deformed vertices of the skin vertex finite element units, wherein the role animation model is used for solving the position information of the vertices of the skin mesh corresponding to the deformation.
The role animation model creating device acquires a finite element mesh, a skin mesh and a skeleton mesh, wherein the finite element mesh comprises a muscle fiber direction, and the expansion or contraction direction of the finite element mesh is determined by the muscle fiber direction when the finite element mesh deforms; obtaining skin vertex centroid interpolation weight according to the vertex position information of the skin mesh and the skin vertex finite element unit to realize embedding the skin mesh into the finite element mesh, and obtaining skeleton vertex centroid interpolation weight according to the vertex position information of the skeleton mesh and the skeleton vertex finite element unit to realize embedding the skeleton mesh into the finite element mesh; fusing to obtain a quasi-static equation based on the skeleton vertex centroid interpolation weight and the elastic potential energy function of the finite element grid; and obtaining a character animation model based on the skin vertex centroid interpolation weight and the quasi-static equation, and establishing an incidence relation among the skin mesh, the finite element mesh and the skeleton mesh through the character animation model. Therefore, the skeleton mesh or other external loads of the character animation model drive the movement or deformation of the finite element mesh, then the movement or deformation of the skin mesh is driven by the movement or deformation of the finite element mesh, and when the nonlinear volume deformation of the finite element mesh occurs, the deformation direction and the deformation degree of the skin mesh can be adaptively adjusted through the muscle fiber direction.
For the specific definition of the means for creating the character animation model, reference may be made to the above definition of the method for creating the character animation model, and details thereof will not be repeated here. The various modules in the above-described apparatus for creating a character animation model may be implemented in whole or in part by software, hardware, and combinations thereof. The modules can be embedded in a hardware form or independent from a processor in the computer device, and can also be stored in a memory in the computer device in a software form, so that the processor can call and execute operations corresponding to the modules.
In one embodiment, a computer device is provided, which may be a terminal, and its internal structure diagram may be as shown in fig. 15. The computer device includes a processor, a memory, a communication interface, a display screen, and an input device connected by a system bus. Wherein the processor of the computer device is configured to provide computing and control capabilities. The memory of the computer device comprises a nonvolatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operation of an operating system and computer programs in the non-volatile storage medium. The communication interface of the computer device is used for carrying out wired or wireless communication with an external terminal, and the wireless communication can be realized through WIFI, a mobile cellular network, NFC (near field communication) or other technologies. The computer program when executed by a processor implements a method of creating a character animation model. The display screen of the computer equipment can be a liquid crystal display screen or an electronic ink display screen, and the input device of the computer equipment can be a touch layer covered on the display screen, a key, a track ball or a touch pad arranged on the shell of the computer equipment, an external keyboard, a touch pad or a mouse and the like.
Those skilled in the art will appreciate that the architecture shown in fig. 15 is merely a block diagram of some of the structures associated with the disclosed aspects and is not intended to limit the computing devices to which the disclosed aspects apply, as particular computing devices may include more or less components than those shown, or may combine certain components, or have a different arrangement of components.
In one embodiment, a computer device is further provided, which includes a memory and a processor, the memory stores a computer program, and the processor implements the steps of the above method embodiments when executing the computer program.
In an embodiment, a computer-readable storage medium is provided, in which a computer program is stored which, when being executed by a processor, carries out the steps of the above-mentioned method embodiments.
In one embodiment, a computer program product or computer program is provided that includes computer instructions stored in a computer-readable storage medium. The computer instructions are read by a processor of a computer device from a computer-readable storage medium, and the computer instructions are executed by the processor to cause the computer device to perform the steps in the above-mentioned method embodiments.
It will be understood by those skilled in the art that all or part of the processes of the methods of the embodiments described above can be implemented by hardware instructions of a computer program, which can be stored in a non-volatile computer-readable storage medium, and when executed, can include the processes of the embodiments of the methods described above. Any reference to memory, storage, database or other medium used in the embodiments provided herein can include at least one of non-volatile and volatile memory. Non-volatile Memory may include Read-Only Memory (ROM), magnetic tape, floppy disk, flash Memory, optical storage, or the like. Volatile Memory can include Random Access Memory (RAM) or external cache Memory. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM), among others.
The technical features of the above embodiments can be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the above embodiments are not described, but should be considered as the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present application, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims (10)

1. A method for creating an animated character model, the method comprising:
acquiring a finite element mesh, a skin mesh and a bone mesh, wherein the finite element mesh comprises a muscle fiber direction, and the expansion or contraction direction of the finite element mesh is determined by the muscle fiber direction when the finite element mesh is deformed;
obtaining skin vertex centroid interpolation weight according to the position information of the vertices of the skin mesh and skin vertex finite element units, wherein the skin vertex finite element units are the finite element units containing the vertices of the skin mesh in the finite element mesh, and the skin vertex centroid interpolation weight represents the position incidence relation between the skin vertex finite element units and the vertices of the skin mesh;
obtaining a bone vertex centroid interpolation weight according to the position information of the vertex of the bone mesh and a bone vertex finite element, wherein the bone vertex finite element is a finite element containing the vertex of the bone mesh in the finite element mesh, and the bone vertex centroid interpolation weight represents the position association relationship between the bone vertex finite element and the vertex of the bone mesh;
based on the skeleton vertex centroid interpolation weight and an elastic potential energy function of the finite element mesh, fusing to obtain a quasi-static equation, wherein the elastic potential energy function is used for representing the elastic potential energy generated by the finite element mesh during deformation, and the quasi-static equation is used for representing the balance degree of the external force and the elastic force applied to the finite element mesh;
and obtaining a role animation model based on the skin vertex centroid interpolation weight and the quasi-static equation, wherein the role animation model establishes an incidence relation among the skin mesh, the finite element mesh and the skeleton mesh.
2. The method of claim 1, wherein fusing to obtain a quasi-static equation based on the bone vertex centroid interpolation weights and the elastic potential energy function of the finite element mesh comprises:
obtaining a bone driving item according to the vertex position information of the bone mesh, the bone vertex centroid interpolation weight, a bone finite element position factor and the volume value fusion of the bone vertex finite element, wherein the bone finite element position factor is the position information of the vertex of the bone vertex finite element, and the bone driving item is used for representing the position difference between the vertex of the bone mesh and the bone vertex finite element;
and fusing the bone driving item and the elastic potential energy function of the finite element grid to obtain a quasi-static equation.
3. The method of claim 2, wherein said fusing the elastic potential energy function of the finite element mesh with the bone driving term to obtain a quasi-static equation comprises:
acquiring a deformation gradient of the finite element mesh, wherein the deformation gradient is used for representing the local deformation degree of the finite element mesh;
performing singular value decomposition on the deformation gradient to obtain a singular value corresponding to the deformation gradient;
obtaining a local elastic potential energy function based on the singular value fusion;
obtaining an elastic potential energy function of the finite element grid based on the local elastic potential energy function fusion;
and fusing the elastic potential energy function of the finite element mesh based on the bone driving item to obtain a quasi-static equation.
4. The method of claim 3, wherein obtaining the deformation gradient of the finite element mesh comprises:
acquiring a pre-factor, wherein the pre-factor is position information of a vertex of a finite element unit in the finite element mesh before initial deformation;
acquiring a post factor, wherein the post factor is position information of vertexes of finite element units in the finite element grid after initial deformation;
and obtaining the deformation gradient of the finite element grid based on the fusion of the pre-factor and the post-factor.
5. The method of claim 3, wherein said fusing a quasi-static equation based on said skeletal drive term and an elastic potential energy function of said finite element mesh comprises:
acquiring a gravity driving item, wherein the gravity driving item represents the gravity action of a gravity field on the finite element grid;
and fusing the bone driving item, the gravity driving item and the elastic potential energy function of the finite element grid to obtain a quasi-static equation.
6. The method of claim 1, wherein deriving a character animation model based on the skin vertex centroid interpolation weights and the quasi-static equation comprises:
obtaining the position information of the finite element grid after the vertex of the finite element unit deforms in a stress balance state by solving the quasi-static equation;
and obtaining the role animation model according to the skin vertex centroid interpolation weight and the position information of the deformed vertices of the skin vertex finite element, wherein the role animation model is used for solving the position information of the vertices of the skin mesh after corresponding deformation.
7. The method of claim 1, wherein the skin mesh is contained within the finite element mesh and the bone mesh is contained within the skin mesh in the character animation model.
8. An apparatus for creating a character animation model, the apparatus comprising:
the mesh acquisition module is used for acquiring a finite element mesh, a skin mesh and a skeleton mesh, wherein the finite element mesh comprises a muscle fiber direction, and the expansion or contraction direction of the finite element mesh is determined by the muscle fiber direction when the finite element mesh is deformed;
the skin vertex centroid interpolation weight generation module is used for obtaining skin vertex centroid interpolation weights according to the position information of the vertices of the skin mesh and skin vertex finite element units, the skin vertex finite element units are finite element units containing the vertices of the skin mesh in the finite element mesh, and the skin vertex centroid interpolation weights represent the position incidence relation between the finite element units and the vertices of the skin mesh;
a skeleton vertex centroid interpolation weight generation module, configured to obtain a skeleton vertex centroid interpolation weight according to position information of vertices of the skeleton mesh and skeleton vertex finite element units, where the skeleton vertex finite element units are finite element units in the finite element mesh that include vertices of the skeleton mesh, and the skeleton vertex centroid interpolation weight represents a position association relationship between the finite element units and the vertices of the skeleton mesh;
the quasi-static equation generation module is used for fusing to obtain a quasi-static equation based on the skeleton vertex centroid interpolation weight and the elastic potential energy function of the finite element mesh, wherein the elastic potential energy function is used for representing the elastic potential energy generated by the finite element mesh during deformation, and the quasi-static equation is used for representing the balance degree of the external force and the elastic force applied to the finite element mesh;
and the character animation model generation module is used for obtaining a character animation model based on the skin vertex centroid interpolation weight and the quasi-static equation, and the character animation model establishes an incidence relation among the skin mesh, the finite element mesh and the skeleton mesh.
9. A computer device comprising a memory and a processor, the memory storing a computer program, characterized in that the processor, when executing the computer program, implements the steps of the method of any of claims 1 to 7.
10. A computer-readable storage medium, in which a computer program is stored which, when being executed by a processor, carries out the steps of the method according to any one of claims 1 to 7.
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