MathEngine Collision

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MathEngine - Collision

• Bent Dalgaard Larsen
• _at_imm.dtu.dk

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Overview

• The design of the collision engine
• What the collision engine can do for you
• How to use the collision engine
• Integrating physics with the collision engine

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Design of the collision engine

• Designed to give the information needed for a
  physics engine. Collision true/false is just
  not good enough.
• Physics engine is not restricted to be MathEngine
• Farfield and nearfield testing
• Farfield testing is the so called n-body
  processing problem, i.e. Which collisions should
  be considered
• Nearfield testing finds the excact collision
  point when a collision occurs.

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Structure of an application
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Supported collision types

• Primitives
• Sphere, Box, Plane, Cylinder, Cone
• Non-primitives
• Convex mesh, Hieght field, Particles
• Ray hit
• Response is given as
• Location of contact
• The normal (i.e. what direction to move in order
  to prevent intersection)
• Penetration depth

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Implemented collision types
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Initializing collision types

• All types of used collision objects must be
  registered
• McdPrimitivesRegisterTypes()
• McdPrimitivesRegisterInteractions()
• McdRGHeightFieldRegisterType()
• McdRGHeightFieldRegisterInteractions()
• McdConvexMeshRegisterType()
• McdConvexMeshRegisterInteractions()
• McdInit(McdPrimitivesGetTypeCount()x)

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Building the space

• Creating the collision space
• McdSpace space McdSpaceAxisSortCreate(McdAllAxe
  s,MAX_BODIES,AVE_NEARBY_COUNTMAX_BODIES)
• McdPairHandlerRegisterSpace(space)
• Before building the space insert all models
• McdSpaceBuild(space)

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Creating collision model

• Creating geomtry
• McdGeometry prim McdSphereCreate (radius)
• McdGeometry prim McdBoxCreate (x,y,z)
• McdGeometry prim McdPlaneCreate()
• Creating collision model
• McdModelID model McdModelCreate(prim)
• Defining postion and orientation of primitive
• MeMatrix4 mat (MeMatrix4)malloc(sizeof(MeMatri
  x4))
• McdModelSetTransformPtr(model, mat)
• Inserting the model into collision space
• McdSpaceInsertModel(space,model)

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Getting results

• First update the collisions
• McdPairHandlerUpdate()
• McdSpacePair pairsMAX_NUM_PAIRS
• int pairs McdSpaceGetNewPairs(space, pairs,
  MAX_NUM_PAIRS)
• McdIntersectResult result
• McdIntersect(pairs0, result)
• The collision results can now be read from result

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Dynamic Toolkit Bridge

• You could write the code inbetween the Collision
  Toolkit and Dynaimc Toolkit yourself
• Or you could just use the Dynamic Toolkit Bridge
• The bridge is prefixed with McdDt
• The problem
• Creating a connection between MdtBody and
  McdModel

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Programming the bridge

• Initialize the bridge
• McdDtBridgeInit()
• McdDtBridgeID bridge McdDtBridgeCreate()
• Connecting McdBodyID and
• McdDtBridgeSetBody(bridge,model, body)
• Now there is no need to handle collisions
  yourself anymore.

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Defining collision parameters

• Now that the bridge handles the contact. How to
  get properties such as bouncyness
• params McdDtBridgeGetContactParams(0, 0)

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Advanced feature - compositing

• If you e.g. want to make a chair you need to put
  several objects together.
• MeMatrix m2Rel, m2Compound
• McdDtBridgeSetBody(bridge, model1, body)
• McdDtBridgeSetBody(bridge, model2, body)
• McdDtBridgeSetRelativeTransformPtr(bridge,
  model2, m2Rel, m2Compound)
• If the two objects collide you need to disable
  the collision detection between these two objects
• McdModelSetInteractionDisabled(model1, model2)