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CharactersCharacters

The Characters are the Actors of the Games.The Characters are the Actors of the Games. Three Types of Characters :Three Types of Characters :

– SegmentedSegmented– MeshMesh– Bone-skinBone-skin

Root-base ConceptRoot-base Concept Production :Production :

– 3D animation tools3D animation tools» 3dsMax3dsMax» MayaMaya» SoftimageSoftimage» ……

– Motion capture (Mocap)Motion capture (Mocap)» For motion dataFor motion data

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IntroductionIntroduction

Base

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A character is composed by a set of models A character is composed by a set of models with motion data to simulate a live creature with motion data to simulate a live creature in real worldin real world

BenefitsBenefits– Hierarchical structureHierarchical structure– Easy to implement in a scene treeEasy to implement in a scene tree

DrawbacksDrawbacks– Segment-likeSegment-like

A Segmented CharacterA Segmented Character

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Vertex animation on skinsVertex animation on skins– Animated positional data on skinsAnimated positional data on skins– 3D warping3D warping

BenefitsBenefits– Easy to implementEasy to implement– Flexible mesh in animationFlexible mesh in animation

DrawbacksDrawbacks– No hierarchyNo hierarchy– No keyframesNo keyframes– Massive datasetMassive dataset

A Mesh CharacterA Mesh Character

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Bone-Skin SkeletonBone-Skin Skeleton– Hierarchical Hierarchical bbonesones– Skin deformation Skin deformation run-timelyrun-timely

BenefitsBenefits– Hierarchical structureHierarchical structure– Not segmented lookNot segmented look

DrawbacksDrawbacks– More complicated than the More complicated than the

other solutionsother solutions– Skin deformation need more Skin deformation need more

CPU cost than transformation CPU cost than transformation onlyonly

Bone A

Skin

Bone B

A Bone-skin CharacterA Bone-skin Character

Euler AnglesEuler Angles Angular DisplacementAngular Displacement QuaternionQuaternion

– SlerpSlerp Converted into (4x4) matrix for computationConverted into (4x4) matrix for computation

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Motion DataMotion Data

Data AcquiredData Acquired– From skin to joint (Mocap)From skin to joint (Mocap)– From joint to skeleton (Post-processing)From joint to skeleton (Post-processing)– From skeleton to skin (In-game)From skeleton to skin (In-game)

DeviceDevice The Shooting PlanThe Shooting Plan

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Optical Motion CaptureOptical Motion Capture

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Raw Data (Positional Data)

Joint

End Point

Bio-Data

Data Acquirement During the MocapData Acquirement During the Mocap

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Skeletons Skin

Skeletons

Bone-Skin

Bone-skin Implementation In GameBone-skin Implementation In Game

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Mocap DevicesMocap Devices

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Starting Out – Reviewing the Animation List and Flowchart

Planning a Mocap ShootPlanning a Mocap Shoot

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Creating a Shot List Create a Database File Names Preliminary Shot List

A Data Record of Shot List

14A Shoot List

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Getting Ready for the Shoot When to Shoot ? Find a Studio Make Sure No Technical Blocks Casting

Preparing a Shooting Schedule Organize the Shot List Daily Schedule Do You Need a Rehearsal Day ?

Take Care of Your Performer

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A Daily Schedule

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Perform motion capture for a ball ?

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Apply motion data on bonesApply motion data on bones

A : parent nodeA : parent node

B : child nodeB : child node

Joint = pivot(px,py,pz) in A

A

B

(x,y,z,,axis)

(,axis)

<v’> = <V> [RB][TB][RA][TA]

From pivot From position

Motion for CharactersMotion for Characters

The above formula is in the left-hand form (Direct3D). What is the formula in the right-hand form (OpenGL)?

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To Create More Animation from Limited OnesTo Create More Animation from Limited Ones RRun-time or Pre-processingun-time or Pre-processing IIssues :ssues :

– MMotion re-targetingotion re-targeting» Run-timeRun-time» http://www.cs.wisc.edu/graphics/Gallery/Retarget/http://www.cs.wisc.edu/graphics/Gallery/Retarget/

– RRe-key-framing (key-frame: e-key-framing (key-frame: http://en.wikipedia.org/wiki/Key_framehttp://en.wikipedia.org/wiki/Key_frame))» Pre-processingPre-processing

– IInterpolationnterpolation» Run-timeRun-time

– MMotion blendingotion blending» Run-timeRun-time

Motion EditingMotion Editing

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A set of frame data to describe the A set of frame data to describe the character’s motioncharacter’s motion

WWalk, Run, Attack, …alk, Run, Attack, …

KKeyframed or Non-keyframedeyframed or Non-keyframed

walk run attack fall

PosesPoses

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walkraw_start_frame raw_end_frame

cut_frame

Parameter { raw_start_frame raw_end_frame start_frame end_frame cut_frame play_speed length transition_mode}

start_frame end_frame

A Pose Definition ExampleA Pose Definition Example

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walk

0 4 8

Frame 5.3

1. If the motion data is in quaternion form2. Get the motion data on frame 5 & 63. Convert the data into quaternion format4. Apply slerp(5, 6, 0.3) to get the interpolation on frame 5.35. Convert the result of step 3 into a rotation matrix6. Apply the matrix to the object for its transformation

Play a PosePlay a Pose

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Pose 1

Pose 2

cut_frame

start_frame

length

Pose ConnectionPose Connection

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Motion blending in run-timeMotion blending in run-time QQuaternion is useduaternion is used ““ Blend Tree”Blend Tree”

CCross fadeross fade CCountinuous blendingountinuous blending FFeather blendingeather blending Drawback: Not working well if the transitions are Drawback: Not working well if the transitions are

from not similar animationsfrom not similar animations

Ref: Ref: http://www.gamasutra.com/features/20030704/edsall_02.shtml

Pose BlendingPose Blending

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RReferenceeference– GGame ame DevelopersDevelopers Conference 2003 Conference 2003– PProceedings CD, Programming Trackroceedings CD, Programming Track– ““AAnimation Blending : Achieving Inverse nimation Blending : Achieving Inverse

Kinematics and More”Kinematics and More”– JJ erry Edsallerry Edsall– MMech Warrior blend treeech Warrior blend tree

Fall Transition

ForwardMotion

FallDown

Walk

Run

Blend TreeBlend Tree

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Pose 1

Pose2

0

1

0

1

Cross FadeCross Fade

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Pose 1

Pose 2

0

1

0

1

Continuous BlendingContinuous Blending

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左右搏擊左右搏擊

Pose 1 Pose 2

Pose 3

Feather BlendingFeather Blending

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Weights to Assign the Influences of the Weights to Assign the Influences of the Deformation by Bones on Skin VerticesDeformation by Bones on Skin Vertices– 1-weight1-weight– 2-weight2-weight– N-weightN-weight

CCPU costPU cost IIt’s Very Good for GPU to Perform the t’s Very Good for GPU to Perform the

Calculation Using Vertex ShaderCalculation Using Vertex Shader

Skin DeformationSkin Deformation

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Bone A(root object)

Bone B(Bone A’s child)

base

base

1. Apply motion data to bones2. Convert the vertex from “base” space to its associated

bone’s space using the natural pose’s inverse transformation

3. Multiple the influence weight4. Accumulate all influences5. Then the vertex is deformed by the bone in “base” space

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Mb = RbTpivot

Ma = RaTposition

Mvb = Mnb-1 MbMa

Mva = Mna-1Ma

vin_base = vs*waMva + vs*wbMvb

A two-weight skin vertex example