149 lines
6.0 KiB
Plaintext
149 lines
6.0 KiB
Plaintext
README for GeomTransformGroup by Tim Schmidt.
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---------------------------------------------
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This is a patch to add the dGeomTransformGroup object to the list of geometry
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objects.
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It should work with the cvs version of the ode library from 07/24/2002.
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++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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comment by russ smith: this code is easy to use with the rest of ODE.
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simply copy GeomTransformGroup.cpp to ode/src and copy GeomTransformGroup.h
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to include/ode. then add GeomTransformGroup.cpp to the ODE_SRC variable
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in the makefile. rebuild, and you're done! of course i could have done all
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this for you, but i prefer to keep GeomTransformGroup separated from the
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rest of ODE for now while other issues with the collision system are
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resolved.
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++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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Description:
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The dGeomTransformGroup is an adaption of the TransformGroup known from
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Java3D (and maybe other libraries with a similar scene graph representation).
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It can be used to build an arbitrarily structured tree of objects that are
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each positioned relative to the particular parent node.
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If you have a plane for example, there is one root node associated with the
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plane's body and another three transformgroups placed 'under' this node. One
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with the fuselage (cappedcylinder) under it and two with the underlying wings
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(flat boxes). And if you want to add engines, simply put them 'next to' the
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wings under another two transformgroups.
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bodyTG ---> associated with dBody
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+--fuselageTG
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| +--fuselageCylinder
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+--leftwingTG
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| +--wingBox
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| +--leftengineTG
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| +--leftengineCylinder
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+--rightwingTG
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+--wingBox
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+--rightengineTG
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+--rightengineCylinder
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This is a method to easily compose objects without the necessity of always
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calculating global coordinates. But apart from this there is something else
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that makes dGeomTransformGroups very valuable.
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Maybe you remember that some users reported the problem of acquiring the
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correct bodies to be attached by a contactjoint in the nearCallback when
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using dGeomGroups and dGeomTransforms at the same time. This results from the
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fact that dGeomGroups are not associated with bodies while all other
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geometries are.
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So, as you can see in the nearCallback of the the test_buggy demo you have to
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attach the contactjoint with the bodies that you get from the geometries that
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are stored in the contact struct (-> dGeomGetBody(contacts[i].geom.g1)).
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Normally you would do this by asking o1 and o2 directly with dGeomGetBody(o1)
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and dGeomGetBody(o2) respectively.
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As a first approach you can overcome that problem by testing o1 and o2 if
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they are groups or not to find out how to get the corresponding bodies.
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However this will fail if you want grouped transforms that are constructed
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out of dGeomTransforms encapsulated in a dGeomGroup. According to the test
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you use contacts[i].geom.g1 to get the right body. Unfortunately g1 is
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encapsulated in a transform and therefore not attached to any body. In this
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case the dGeomTransform 'in the middle' would have been the right object to
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be asked for the body.
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You may now conclude that it is a good idea to unwrap the group encapsulated
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geoms at the beginning of the nearcallback and use dGeomGetBody(o1)
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consistently. But keep in mind that this also means not to invoke
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dCollide(..) on groups at all and therefore not to expoit the capability of
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dGeomGroups to speed up collision detection by the creation of bounding boxes
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around the encapsulated geometry.
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Everything becomes even worse if you create a dGeomTransform that contains a
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dGeomGroup of geoms. The function that cares about the collision of
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transforms with other objects uses the position and rotation of the
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respective encapsulated object to compute its final position and orientation.
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Unfortunately dGeomGroups do not have a position and rotation, so the result
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will not be what you have expected.
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Here the dGeomTransformGroups comes into operation, because it combines the
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advantages and capabilities of the dGeomGroup and the dGeomTransform.
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And as an effect of synergy it is now even possible to set the position of a
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group of geoms with one single command.
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Even nested encapsulations of dGeomTransformGroups in dGeomTransformGroups
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should be possible (to be honest, I have not tried that so far ;-) ).
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++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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API:
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dGeomID dCreateGeomTransformGroup (dSpaceID space);
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- create a GeomTransformGroup
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void dGeomTransformGroupAddGeom (dGeomID tg, dGeomID obj);
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- Comparable to dGeomTransformSetGeom or dGeomGroupAdd
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- add objects to this group
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void dGeomTransformGroupRemoveGeom (dGeomID tg, dGeomID obj);
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- remove objects from this group
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void dGeomTransformGroupSetRelativePosition
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(dGeomID g, dReal x, dReal y, dReal z);
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void dGeomTransformGroupSetRelativeRotation
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(dGeomID g, const dMatrix3 R);
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- Comparable to setting the position and rotation of all the
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dGeomTransform encapsulated geometry. The difference
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is that it is global with respect to this group and therefore
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affects all geoms in this group.
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- The relative position and rotation are attributes of the
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transformgroup, so the position and rotation of the individual
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geoms are not changed
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const dReal * dGeomTransformGroupGetRelativePosition (dGeomID g);
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const dReal * dGeomTransformGroupGetRelativeRotation (dGeomID g);
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- get the relative position and rotation
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dGeomID dGeomTransformGroupGetGeom (dGeomID tg, int i);
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- Comparable to dGeomGroupGetGeom
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- get a specific geom of the group
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int dGeomTransformGroupGetNumGeoms (dGeomID tg);
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- Comparable to dGeomGroupGetNumGeoms
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- get the number of geoms in the group
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++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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Tim Schmidt
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student of computer science
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University of Paderborn, Germany
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tisch@uni-paderborn.de
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