Open Dynamics Engine
Classes | Modules | Functions

World

Classes

struct  dWorldStepReserveInfo
 Memory reservation policy descriptor structure for world stepping functions. More...

Modules

 Automatic Enabling and Disabling
 Damping

Functions

ODE_API dWorldID dWorldCreate (void)
 Create a new, empty world and return its ID number.
ODE_API void dWorldDestroy (dWorldID world)
 Destroy a world and everything in it.
ODE_API void dWorldSetGravity (dWorldID, dReal x, dReal y, dReal z)
 Set the world's global gravity vector.
ODE_API void dWorldGetGravity (dWorldID, dVector3 gravity)
 Get the gravity vector for a given world.
ODE_API void dWorldSetERP (dWorldID, dReal erp)
 Set the global ERP value, that controls how much error correction is performed in each time step.
ODE_API dReal dWorldGetERP (dWorldID)
 Get the error reduction parameter.
ODE_API void dWorldSetCFM (dWorldID, dReal cfm)
 Set the global CFM (constraint force mixing) value.
ODE_API dReal dWorldGetCFM (dWorldID)
 Get the constraint force mixing value.
ODE_API int dWorldUseSharedWorkingMemory (dWorldID w, dWorldID from_world)
 Set the world to use shared working memory along with another world.
ODE_API void dWorldCleanupWorkingMemory (dWorldID w)
 Release internal working memory allocated for world.
ODE_API int dWorldSetStepMemoryReservationPolicy (dWorldID w, const dWorldStepReserveInfo *policyinfo)
 Set memory reservation policy for world to be used with simulation stepping functions.
ODE_API int dWorldSetStepMemoryManager (dWorldID w, const dWorldStepMemoryFunctionsInfo *memfuncs)
 Set memory manager for world to be used with simulation stepping functions.
ODE_API int dWorldStep (dWorldID w, dReal stepsize)
 Step the world.
ODE_API int dWorldQuickStep (dWorldID w, dReal stepsize)
 Quick-step the world.
ODE_API void dWorldImpulseToForce (dWorldID, dReal stepsize, dReal ix, dReal iy, dReal iz, dVector3 force)
 Converts an impulse to a force.
ODE_API void dWorldSetQuickStepNumIterations (dWorldID, int num)
 Set the number of iterations that the QuickStep method performs per step.
ODE_API int dWorldGetQuickStepNumIterations (dWorldID)
 Get the number of iterations that the QuickStep method performs per step.
ODE_API void dWorldSetQuickStepW (dWorldID, dReal over_relaxation)
 Set the SOR over-relaxation parameter.
ODE_API dReal dWorldGetQuickStepW (dWorldID)
 Get the SOR over-relaxation parameter.
ODE_API void dWorldSetContactMaxCorrectingVel (dWorldID, dReal vel)
 Set the maximum correcting velocity that contacts are allowed to generate.
ODE_API dReal dWorldGetContactMaxCorrectingVel (dWorldID)
 Get the maximum correcting velocity that contacts are allowed to generated.
ODE_API void dWorldSetContactSurfaceLayer (dWorldID, dReal depth)
 Set the depth of the surface layer around all geometry objects.
ODE_API dReal dWorldGetContactSurfaceLayer (dWorldID)
 Get the depth of the surface layer around all geometry objects.

Detailed Description

The world object is a container for rigid bodies and joints. Objects in different worlds can not interact, for example rigid bodies from two different worlds can not collide.

All the objects in a world exist at the same point in time, thus one reason to use separate worlds is to simulate systems at different rates. Most applications will only need one world.


Function Documentation

ODE_API void dWorldCleanupWorkingMemory ( dWorldID  w)

Release internal working memory allocated for world.

The worlds allocate working memory internally for simulation stepping. This function can be used to free world's internal memory cache in case if number of objects/joints in the world decreases significantly. By default, internal allocation policy is used to only increase cache size as necessary and never decrease it.

If a world shares its working memory with other worlds the cache deletion affects all the linked worlds. However the shared status itself remains intact.

The function call does affect neither memory reservation policy nor memory manager.

Parameters:
wThe world to release working memory for.
See also:
dWorldUseSharedWorkingMemory
dWorldSetStepMemoryReservationPolicy
dWorldSetStepMemoryManager
ODE_API dWorldID dWorldCreate ( void  )

Create a new, empty world and return its ID number.

Returns:
an identifier
ODE_API void dWorldDestroy ( dWorldID  world)

Destroy a world and everything in it.

This includes all bodies, and all joints that are not part of a joint group. Joints that are part of a joint group will be deactivated, and can be destroyed by calling, for example, dJointGroupEmpty().

Parameters:
worldthe identifier for the world the be destroyed.
ODE_API dReal dWorldGetCFM ( dWorldID  )

Get the constraint force mixing value.

Returns:
CFM value
ODE_API dReal dWorldGetContactSurfaceLayer ( dWorldID  )

Get the depth of the surface layer around all geometry objects.

Returns:
the depth
ODE_API dReal dWorldGetERP ( dWorldID  )

Get the error reduction parameter.

Returns:
ERP value
ODE_API int dWorldGetQuickStepNumIterations ( dWorldID  )

Get the number of iterations that the QuickStep method performs per step.

Returns:
nr of iterations
ODE_API dReal dWorldGetQuickStepW ( dWorldID  )

Get the SOR over-relaxation parameter.

Returns:
the over-relaxation setting
ODE_API void dWorldImpulseToForce ( dWorldID  ,
dReal  stepsize,
dReal  ix,
dReal  iy,
dReal  iz,
dVector3  force 
)

Converts an impulse to a force.

Remarks:
If you want to apply a linear or angular impulse to a rigid body, instead of a force or a torque, then you can use this function to convert the desired impulse into a force/torque vector before calling the BodyAdd... function. The current algorithm simply scales the impulse by 1/stepsize, where stepsize is the step size for the next step that will be taken. This function is given a dWorldID because, in the future, the force computation may depend on integrator parameters that are set as properties of the world.
ODE_API int dWorldQuickStep ( dWorldID  w,
dReal  stepsize 
)

Quick-step the world.

This uses an iterative method that takes time on the order of m*N and memory on the order of m, where m is the total number of constraint rows N is the number of iterations. For large systems this is a lot faster than dWorldStep(), but it is less accurate.

QuickStep is great for stacks of objects especially when the auto-disable feature is used as well. However, it has poor accuracy for near-singular systems. Near-singular systems can occur when using high-friction contacts, motors, or certain articulated structures. For example, a robot with multiple legs sitting on the ground may be near-singular.

There are ways to help overcome QuickStep's inaccuracy problems:

  • Increase CFM.
  • Reduce the number of contacts in your system (e.g. use the minimum number of contacts for the feet of a robot or creature).
  • Don't use excessive friction in the contacts.
  • Use contact slip if appropriate
  • Avoid kinematic loops (however, kinematic loops are inevitable in legged creatures).
  • Don't use excessive motor strength. force-based motors instead of velocity-based motors.

Increasing the number of QuickStep iterations may help a little bit, but it is not going to help much if your system is really near singular.

Failure result status means that the memory allocation has failed for operation. In such a case all the objects remain in unchanged state and simulation can be retried as soon as more memory is available.

Parameters:
wThe world to be stepped
stepsizeThe number of seconds that the simulation has to advance.
Returns:
1 for success and 0 for failure
ODE_API void dWorldSetCFM ( dWorldID  ,
dReal  cfm 
)

Set the global CFM (constraint force mixing) value.

Parameters:
cfmTypical values are in the range {10^{-9}} -- 1. The default is 10^-5 if single precision is being used, or 10^-10 if double precision is being used.
ODE_API void dWorldSetContactMaxCorrectingVel ( dWorldID  ,
dReal  vel 
)

Set the maximum correcting velocity that contacts are allowed to generate.

Parameters:
velThe default value is infinity (i.e. no limit).
Remarks:
Reducing this value can help prevent "popping" of deeply embedded objects.
ODE_API void dWorldSetContactSurfaceLayer ( dWorldID  ,
dReal  depth 
)

Set the depth of the surface layer around all geometry objects.

Remarks:
Contacts are allowed to sink into the surface layer up to the given depth before coming to rest.
Parameters:
depthThe default value is zero.
Remarks:
Increasing this to some small value (e.g. 0.001) can help prevent jittering problems due to contacts being repeatedly made and broken.
ODE_API void dWorldSetERP ( dWorldID  ,
dReal  erp 
)

Set the global ERP value, that controls how much error correction is performed in each time step.

Parameters:
dWorldIDthe identifier of the world.
erpTypical values are in the range 0.1--0.8. The default is 0.2.
ODE_API void dWorldSetGravity ( dWorldID  ,
dReal  x,
dReal  y,
dReal  z 
)

Set the world's global gravity vector.

The units are m/s^2, so Earth's gravity vector would be (0,0,-9.81), assuming that +z is up. The default is no gravity, i.e. (0,0,0).

ODE_API void dWorldSetQuickStepNumIterations ( dWorldID  ,
int  num 
)

Set the number of iterations that the QuickStep method performs per step.

Remarks:
More iterations will give a more accurate solution, but will take longer to compute.
Parameters:
numThe default is 20 iterations.
ODE_API void dWorldSetQuickStepW ( dWorldID  ,
dReal  over_relaxation 
)

Set the SOR over-relaxation parameter.

Parameters:
over_relaxationvalue to use by SOR
ODE_API int dWorldSetStepMemoryManager ( dWorldID  w,
const dWorldStepMemoryFunctionsInfo memfuncs 
)

Set memory manager for world to be used with simulation stepping functions.

The function allows to customize memory manager to be used for internal memory allocation during simulation for a world. By default, dAlloc/dRealloc/dFree based memory manager is used.

Passing memfuncs argument as NULL results in memory manager being reset to default one as if the world has been just created. The content of memfuncs structure is copied internally and does not need to remain valid after the call returns.

If the world uses working memory sharing, changing memory manager affects all the worlds linked together.

Failure result status means a memory allocation failure.

Parameters:
wThe world to change memory reservation policy for.
memfuncsNull or a pointer to memory manager descriptor structure.
Returns:
1 for success and 0 for failure.
See also:
dWorldUseSharedWorkingMemory
ODE_API int dWorldSetStepMemoryReservationPolicy ( dWorldID  w,
const dWorldStepReserveInfo policyinfo 
)

Set memory reservation policy for world to be used with simulation stepping functions.

The function allows to customize reservation policy to be used for internal memory which is allocated to aid simulation for a world. By default, values of dWORLDSTEP_RESERVEFACTOR_DEFAULT and dWORLDSTEP_RESERVESIZE_DEFAULT are used.

Passing policyinfo argument as NULL results in reservation policy being reset to defaults as if the world has been just created. The content of policyinfo structure is copied internally and does not need to remain valid after the call returns.

If the world uses working memory sharing, changing memory reservation policy affects all the worlds linked together.

Failure result status means a memory allocation failure.

Parameters:
wThe world to change memory reservation policy for.
policyinfoNull or a pointer to policy descriptor structure.
Returns:
1 for success and 0 for failure.
See also:
dWorldUseSharedWorkingMemory
ODE_API int dWorldStep ( dWorldID  w,
dReal  stepsize 
)

Step the world.

This uses a "big matrix" method that takes time on the order of m^3 and memory on the order of m^2, where m is the total number of constraint rows. For large systems this will use a lot of memory and can be very slow, but this is currently the most accurate method.

Failure result status means that the memory allocation has failed for operation. In such a case all the objects remain in unchanged state and simulation can be retried as soon as more memory is available.

Parameters:
wThe world to be stepped
stepsizeThe number of seconds that the simulation has to advance.
Returns:
1 for success and 0 for failure
ODE_API int dWorldUseSharedWorkingMemory ( dWorldID  w,
dWorldID  from_world 
)

Set the world to use shared working memory along with another world.

The worlds allocate working memory internally for simulation stepping. This memory is cached among the calls to dWordStep and dWorldQuickStep. Similarly, several worlds can be set up to share this memory caches thus reducing overall memory usage by cost of making worlds inappropriate for simultaneous simulation in multiple threads.

If null value is passed for from_world parameter the world is detached from sharing and returns to defaults for working memory, reservation policy and memory manager as if just created. This can also be used to enable use of shared memory for a world that has already had working memory allocated privately. Normally using shared memory after a world has its private working memory allocated is prohibited.

Allocation policy used can only increase world's internal reserved memory size and never decreases it. dWorldCleanupWorkingMemory can be used to release working memory for a world in case if number of objects/joint decreases significantly in it.

With sharing working memory worlds also automatically share memory reservation policy and memory manager. Thus, these parameters need to be customized for initial world to be used as sharing source only.

Failure result status means a memory allocation failure.

Parameters:
wThe world to use the shared memory with.
from_worldNull or the world the shared memory is to be used from.
Returns:
1 for success and 0 for failure.
See also:
dWorldCleanupWorkingMemory
dWorldSetStepMemoryReservationPolicy
dWorldSetStepMemoryManager