CS461561 Virtual Environments: Principles

1
CS461/561Virtual Environments Principles
ApplicationsVirtools Physics

• 3-05-2007
• Prof. Searleman
• SC375
• jets_at_clarkson.edu

2
Overview

• HW2
• Quiz2 (after class today)
• simple characters animations
• all BBs in Andys tutorial
• Virtools Physics Tutorial
• C\Program Files\Virtools\Virtools
  4.0\Documentation\Physics\
• web format above...\Physics Users
  Guide\Start.html
• pdf above...\Physics Users Guide\Physics_Library
  .pdf

3
Virtools Physics Package

• for today read the physics tutorial, and do all
  the suggested activities found in
• Chapters 1 2 of Start.html (recommended), or
• Chapters 5 through 12 in Physics_Library.pdf
• for Wednesday continue with the physics tutorial
• HW3 posted VRPong

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Complete for today Physics Tutorial

• 6. Getting Started
• 7. Physics Topology Modeling (p.21)
• 8. Mesh Control
• 9. Concave Hulls
• Concave made of convex.cmo
• Concave made of convex Final.cmo
• 10. Compound Concave Hulls
• 11. Ball Primitives
• Ball Primitive.cmo
• Ball Primitive Final.cmo
• Ball Primitive - Final Reflect_Shadow.cmo
• 12. Level of Detail (LOD)
• Concave Topology LOD.cmo

5
Physics Tutorial

• Start.html (or Chapter 6. Getting Started)
• Getting Started.cmo
• Getting Started Final.cmo
• Getting Started Final Reflection.cmo
• Friction.cmo
• Shadows reflections must add attributes to the
  objects that are casting shadows reflections
• Important concepts
• Physics Engine
• Physicalize Building Block
• Physics Mesh convex concave hulls

6
Physicalize BB
7
Physicalize BB

• Fixed if checked, the object will be considered
  as unmoveable
• Friction
• 0 means no friction at all.
• 0.1 ice.
• 3 very rough.
• Elasticity defines the bouncing property of the
  physics material associated with the object.
• 1.0 means never ending bounces.
• Caution dont give unrealistic values to the
  elasticity. A value too high (say 10) will make
  your simulation very unstable after a while.

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Physicalize BB

• Mass how heavy the object should be tons.
• Caution dont use too small a value if the
  object is to be used as a root object in a
  constraint system (kinematic chain), or too high
  a value if the object is supposed to collide with
  very small objects.
• Collision Group filter string that defines the
  collision rules for this object.
• NULL string ("") means the object will collide
  with every other object.
• Non-NULL string (like "car") means the object
  will collide with every object, except those in
  the same collision group.
• Caution only the first 8 characters will be used
  to determine the real collision group.

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Physicalize BB

• Start Frozen if checked, the object is not
  affect by gravity, until some event awakes it
  (like a collision with another object, an
  impulse, or the creation of a spring attached to
  it).
• This is useful for example, when you need to
  physicalize a lot of objects that already lie on
  the floor, and don't want the physics engine to
  slow down your composition by calculating all the
  needed collisions to stabilize your objects.
• Enable Collision if checked, collisions are
  allowed. If set to FALSE, this boolean value
  overides the "Collision Group", and no collision
  will ever affect the object.
• Shift Mass Center by default the mass center is
  calculated automatically (done when "Automatic
  Calculate Mass Center" is checked).
• You can change this center for a non-barycentric
  object. Shifting the mass center can give your
  object better stability or a somersault effect.
• If the setting "Automatic Calculate Mass Center"
  is TRUE, the "Shift Mass Center" vector won't be
  taken into consideration.
• Otherwise, the "Shift Mass Center Parameter"
  defines the mass center position in the object's
  referential.
• Caution the "Shift Mass Center" parameter is not
  a position in the object space, it only a shift
  from the automatically calculated mass center.

10
Physicalize BB

• Linear Speed Dampening
• 0.0 means no dampening on linear speed
  (translations),
• 1.0 means reduction to 30 each second,
• 0.1 means 90, etc.
• Could be used as sort of air resistance.
• Too low object could accelerate unrealisticly.
• Rot Speed Dampening
• 0.0 means no dampening on rotation speed
• 1.0 means reduction to 30 each second,
• 0.1 means 90, etc.
• Could be used as sort of air resistance.
• Too low object could accelerate unrealisticly.

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Physicalize BB

• Surface Name this parameter lets you give a name
  to the physics surface created for your object,
  or allow you to specify an already created
  surface.
• This parameter is empty at first (when you attach
  the "Physicallize" building block to an object),
  but if you edit it again, you should see that a
  string has been automatically created, based on
  the mesh's name.
• Once an object is physicallized (at run-time), it
  creates a physics surface (topology structure),
  which is stored internally and associated with a
  string value (the one provided by this
  parameter). This physics surface can thus be used
  by any other object whose topology matches this
  object.

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Physicalize BB

• Surface Name (cont.)
• Physics surfaces are the only physics information
  that stay in memory after Restoring Initial
  Conditions (Reset). Thus they can be used even
  after the object is deleted. That's why, when you
  expand the dialog parameter box of a physics
  surface parameter (use the little rectangle on
  the top-left), you get a list of all existing
  physics surfaces.
• From this list you can destroy physics surfaces
  (it's the only way to constrain the physics
  manager to take into consideration a new object's
  topology which name would be the same as an
  existing one). You can also choose to save this
  physics surface in the composition or not
  (allowing the physics manager not to recalculate
  the topology of your object if it's a complex one
  for example). And you can also see how much
  KBytes it takes to keep each physics surfaces in
  memory, or how much it would take to save them
  into the file (except the compression rate).

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Physicalize BB

• Convex the meshes specified here are considered
  as convex, and if they are not, the physics
  engine will only consider their convex hull to
  create the physics object's topology.
• If the "Convex Count" setting is bigger than 1,
  you can compose the topology of your object from
  several convex meshes. Since convex collisions
  computations are cheaper that concave collisions,
  this method can be useful to create concave
  objects from convex ones.
• To do so, all your convex objects must share the
  same position for their local referential. Which
  means, from 3D Studio Max (or any other 3d
  modelling tool), you should first create one
  single concave object, and then cut it into
  convex meshes, this way all the exported convex
  meshes will share the same position (and
  orientation) for their local referential.

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Physicalize BB

• Concave the mesh is considered as concave,
  which means each of its faces are taken as
  individual convex meshes. The computation time to
  simulate such object is larger than for a convex
  object, so keep the number of concave objects
  used in your level as low as possible.
• Typically, one concave object is used for the
  static world (walls, floors, stairs .. etc), and
  moving objects are often convex.
• Ball Radius m when you want your object to be
  simulate as a ball, this parameter lets you
  specify its radius (in meters).
• Convex Count the number of convex elements used
  to compose the physics surface of the physics
  object.
• Concave Count the number of concave elements
  used to compose the physics surface of the
  physics object.

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Physicalize BB

• Use Ball the number of ball elements used to
  compose the physics surface of the physics object
  (for the moment, you can use only 1 ball, and if
  you do so, you must use 0 convex objects and 0
  concave ones.)
• Auto Mass Center if checked, the object's mass
  center will be calculated automatically, and the
  "Shift Mass Center" parameter will be avoid
  (note letting the computer calculate the mass
  center automatically is not time consuming since
  this is done by default).
• Reconstruct Surface if checked, the surface
  (topology info for physics engine) will be
  calculated each time you "physicallize" the
  object. Thus, if a surface with the same name
  than your specified "Surface Name" has already
  been created, it will be destroyed and replaced
  by the new topology you specified.
• Use Convex Hull if checked, the algorithm
  generates an additional convex hull around the
  object. For moveable objects this hull can
  increase performance to the same level as convex
  objects. For huge landscapes this optimization
  makes no sense at all, as all interesting objects
  are penetrating the convex hull all the time.

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Physicalize BB Notes

• Once an object is made part of the physics world
  (ie "Physicallized"), it can no longer be moved
  by standard building blocks (like "Set Position",
  "Rotate" or Translate), unless they are being
  beamed (See "Beam Physics Object") or "motion
  controlled" (See "Motion Controller").
• Moving concave objects is not recommended, but if
  you ever need to use moving concave objects, set
  "Use Convex Hull" to true (object is still
  concave, but an additionnal convex hull is
  computed around the object to speed collision
  detection).
• Hiding a physics object has no influence on the
  physics simulation. Even if it is not visible,
  the object will still react the same (falling,
  colliding, etc). It won't be deleted from the
  physics simulation.
• Remember that sliding motion between two physics
  objects depends on both of their materials.

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Physicalize BB Notes

• Only the first 8 characters of "Collision Group"
  will be used.
• If even after attaching the "Physicallize"
  building block, and editing it again (which
  should create and automatic string) no string is
  used to define the object's physics surface (see
  "Surface Name" parameter), the object will have
  no collision surface (thus no collision
  interaction), and a 1 meter radius ball will be
  used to simulate its inertia.
• The object's physics surface is also used to
  calculate the mass center and the rotation
  inertia of an object. Therefore, the topology
  defined by the convex meshes or the concave one
  not only influences the collision between the
  object and the physics environment, it also
  modulates the way a physics object reacts in the
  air or in a buoyancy volume.
• See Also "UnPhysicallize", "Change Physics
  Properties".

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Complete by Wednesday Physics Tutorial

• 13. Constraint Systems (p.37)
• 14. Spring Constraints
• Springs.cmo
• Springs Final.cmo
• 15. Hinge Constraints
• Fridge.cmo
• Fridge Final.cmo
• 16. Dynamics
• 17. Applying an Impulse (Force)
• Pilling.cmo
• Pilling Impulse - Final.cmo

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Constraint Systems

• Degrees of Freedom (DOF)
• Hinge constraints
• Set Physics Hinge BB
• Ball and Socket constraint
• Set Physics Ball Joint BB
• Slider constraint, Point to Plane constraint,
  generic constraints
• Set Physics Constraint BB
• Spring constraint
• Set Physics Spring BB

20
Applying Forces to Objects

• Linear impulse
• magnitude, direction, point of application, and
  duration
• Physics Impulse BB
• Angular impulse (torque)
• magnitude, axis of rotation, point of
  application, duration
• Physics Torque BB

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Physics Tutorial

• 18. Controlling Motion (p.54)
• Ice.cmo
• Ice Final.cmo
• 19. Removing Physics Objects from the physics
  environment
• Pilling.cmo
• 20. Moving Physics Objects without applying
  forces
• Beaming.cmo (? Missing)
• 21. Dynamic Physics Properties
• snowboard.cmo
• snowboard Final.cmo
• snowboard Final2.cmo

22
Motion Control

• Motion Controller BB
• Entity to Follow the physics object on which the
  "Motion Controller" is applied will try to have
  the same position and orientation as this entity

23
Moving a Physics Object

• Physics Impulse BB

24
Beam me up, Scotty

• Beam Physics Object BB
• Beams a physics object to a new position or
  orientation

25
Removing a physics object

• UnPhysicalize BB

26
Physics Tutorial

• 22. Sample Compositions
• Physics Motor
• Hinge Motor.cmo
• Phantom, Buoyancy, Force Field
• Buoyancy.cmo
• duck.cmo
• Physics Car (raycasting)
• baobab café US.cmo
• raycast car sample.cmo
• cararena.cmo
• car raycast array.nmo
• car pickup array.nmo
• tractor_trailer.cmo