Dynamics in Mayabaraff/sigcourse/slidesh.pdf · SH2 S IGGRAPH ’97 C OURSE N OTES P HYSICALLY B...
Transcript of Dynamics in Mayabaraff/sigcourse/slidesh.pdf · SH2 S IGGRAPH ’97 C OURSE N OTES P HYSICALLY B...
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SH1SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Dynamics in Maya
Gary MonheitAlias | Wavefront
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SH2SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Dynamics in Maya
• Overall Requirements
• Architecture and Features
• Animations
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SH3SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Overall Requirements
• Why Dynamics?
• Problems with traditional animation techniques
• Kinds of dynamics problems
• Requirements for software architecture
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SH4SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Why Dynamics?
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SH5SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Problems with traditional animatio n
• Hard to keyframe
• Rendered polygons don’t give desired effects
• Amorphous effects hard to achieve
• Lacks high−level control, simulation
• Lacks procedural control
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SH6SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Kinds of dynamics problems
Particles
• Contain a set of points in global space with attributes• Affected by dynamic solver• Created at either object creation time or by emitters• Handle birth and death• Support a variety of rendering techniques
Soft Bodies
• Geometry with points updated by a particle object• Superset of all particle features
Rigid Bodies
• Geometry with fixed topology and points• Affected by collisions, constraints, and external forces
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SH7SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Requirements for software architecture
• Integrated
• Extensible
• Reusable
• Tweakable
• Support Relationships
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SH8SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Integrate d
Maya as scene object architecture • Nodes • Attributes • Connections
Keyframing • Any scalar attributes • 3D motion of non−dynamic objects • Keyframe editors are familiar to animators
Layered procedural animation • Output from dynamics can be input to other nodes • Outputs from other nodes can be input to dynamics
Rendering • Rendered within Maya or exported to other renderer • Software rendering (volumetric) • Hardware rendering (openGL)
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SH9SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Extensible
• Maya embedded language (Mel)
• Parameter driven: attributes
• ASCII scene file format
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SH10SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Reusable
• Layered scenes with geometry and effects
• Create your own clipFX with Mel
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SH11SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Tweakable
Attributes are modifiable
• Keyframes • Expressions • Connect to other nodes • Add user−defined attributes
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SH12SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Relationships
• Object−to−object relationships
• Attribute−to−attribute relationships
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SH13SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Dynamics in Maya
• Overall Requirements
• Architecture and Features
• Animations
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SH14SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Architecture & Features
• Maya Architecture
• Dynamic Architecture
• Rendering
• Expressions
• Integrated Dynamics
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SH15SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Maya Architecture (part 1)
• Nodes
• Attributes
• Connections
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SH16SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Maya Architecture (part 2)
• Transforms and Shapes
• DAG: Directed Acyclic Graph
• The "object" is really the transformplus the shape(s)
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SH17SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Dynamics Architecture
• Particles
• Fields• Emitters• Collision Models• Particle Collision Events
• Controllers
• Connectables and Connections
• Soft Bodies• Springs
• Rigid Bodies
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SH18SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Particles
• A particle object is a particle system
• Per−particle (array) attributes vs.scalar attributes
• User−defined attributes
• Particles act independently
• No particle−to−particle collisions
• What affects particles?• Fields• Springs• Attribute values• Expressions (one−line or multi−line)• Dynamics controller attributes
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SH19SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Fields
• Positional fields
• Geometry fields. Example: sphere owns radial field
• Types of fields • Air • Drag • Gravity • Newton • Radial • Turbulence • Uniform • Vortex
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SH20SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Emitters
Emitters • Creates new particles into a particle object • Hose vs. water. Emitter is the hose.
Positional emitter • The transform defines the position, orientation • Parented, keyframed, in IK chain, ...
Geometry emitter • Geometry owns the emitter • Point vs. surface • Particle, NURBS, polygon, lattice, curve ...
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SH21SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Collision Models
• Elasticity
• Friction
• Collision trace depth
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SH22SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Particle Collision Events
• In the event that a particle collides: • Emit • Split • Die
• Optionally call a Mel proc each time the event occurs
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SH23SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Connectables and Connections
Dynamics objects: • Particles • Soft bodies • Rigid bodies Connectable object owns one or more of any combination of: • Fields • Emitters • Collision models
What kind of object can be a connectable: • Polygon, NURBS, lattice, curve, ...
Dynamics object Connectable objectconnect flags
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SH24SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Examples of connections
Description Conn Type Connection
Sphere emits particles emission particles −> sphere
Particles fall under field particles −> gravity gravity
Particles bounce on collision particles −> surface surface
Particles owning radial field soft cube −> particles field repel a soft cube
Point emitter emits emission soft mesh −> pt emitter soft mesh
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SH25SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Controllers
• Manage dynamic objects that may interact
• Interface to a differential equations solver
• Necessary so that all dynamics objects get updated in sync
• Hold global attributes for dynamics
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SH26SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Goals
• Goals are geometry, particles, or soft bodies referenced in a particle object
• Create a force for each particle to move toward a pointon the goal
• Particles or soft bodies can have multiple goals
• Does not require the same number of points as target
• Individual goal weight 0 to 1
• Attribute goalPP 0 to 1 (per−particle)
• Dynamics weight 0 to 1 for the forces generated by fields and collisions
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SH27SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Springs
• Classical mechanics spring
• Hook’s Law
• Stiffness and damping
• Start force weight, end force weight
• 0 to 1• Amount of the force of the spring that gets applied
to either start or end point• (0, 1) or (1, 0) simulates nailing one end of the spring
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SH28SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Soft bodies
• Soft is a command, not a node
• For the user, soft bodies are geometry whose points are updated by a particle object
• Internally, soft bodies are the particle object
• Geometry converted or duplicated in a soft body
• Springs generated by min−max distance or by walk length
• Oversampling (small solver step size) stabilize springs
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SH29SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Rigid Bodies
• Nodes
• Rigid body
• Constraints • Nail • Pin • Hinge • Spring • Barrier
• Transformations updated by a solver that applies forces
• Internal constraints added implicitly (by contact) or explicitly (by constraint objects)
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SH30SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Rigid Body Features
• Contact forces handled for resting and sliding objects
• Static and dynamic friction
• Active rigid body• collision detection• dynamic response
• Passive rigid body• collision detection• independent control by keyframes, expressions,
other nodes
• Cache motion
• Collision layers used to reduce complexity
• Choice of 3 kinds of solvers
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SH31SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Renderin g
• Render Types
• Hardware Rendering in OpenGL
• Software Rendering
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SH32SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Render Types
• Point• Multi−point
• Streak (lines)• Multi−streak
• Sprites (textures)
• Sphere• Geometry
• Numeric (for debugging)
• Tube (Software)• Cloud (Software)• Blobby Surface (Software)
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SH33SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Software renderin g
• Volumetric rendering
• Blobby surface render type uses any shader
• Tube and Cloud render types use specificparticle cloud shader
• Future: hair shader
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SH34SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Expressions
• Mel Language
• Attribute Expressions
• Particle Expressions
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SH35SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Mel Language
• Maya Embedded L anguage
• Unified language for file format, commandengine, and expressions
• Like C
• Like shell
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SH36SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Attribute Expressions
• Lazy evaluation − evaluate when needed
• Multi−line expressions
• Multiple input and output attributes
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SH37SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Particle Expressions
• Particle expressions executed per−particle• Multi−line expressions are like small programs• Any attribute accessible for setting and getting values• Run−time vs. creation rules• Built−in functions for math, system, I/O, arrays• Data types: int, float, string, vector
int[], float[], string[], vector[]• Maya commands can be called from expressions
Example:
// Creation rule for setting color: dynExpression −c −at rgbPP −s "rgbPP = sphrand(1);" colorCloud;
// Runtime rule for setting color: dynExpression −r −at rgbPP −s "if( age > .5 ) rgbPP += <<0,0,rand(.1)>>;" colorCloud;
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SH38SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Integrated Dynamics
• Dynamics and transforms
• Rigid Bodies − active and passive
• Soft Body, curves, and IK chain
• Soft Body and deformers
• Soft Body, Rigid Body, and goals
• Particle collision events ...
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SH39SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Dynamics in Maya
• Overall Requirements
• Architecture and Features
• Animations
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SH40SIGGRAPH ’97 COURSE NOTES PHYSICALLY BASED MODELING
Future Work
• Maya 2.0