[SOLVED] What is TopologyEngine for ?

[Weng]

What is TopologyEngine for ?

In BaseObject.h

the method “handleTopologyChange” is commented as “@deprecated topological changes now rely on TopologyEngine” :

/// Handle topological Changes
/// @deprecated topological changes now rely on TopologyEngine
virtual void handleTopologyChange() {}

/// Handle topological Changes from a given Topology
/// @deprecated topological changes now rely on TopologyEngine
virtual void handleTopologyChange(core::topology::Topology* t);

Also, in BaseMechanicalState.h, “handleStateChange” is commented as “@deprecated topological changes now rely on TopologyEngine” :

/// Handle state Changes
/// @deprecated topological changes now rely on TopologyEngine
virtual void handleStateChange() {}

/// Handle state Changes from a given Topology
/// @deprecated topological changes now rely on TopologyEngine
virtual void handleStateChange(core::topology::Topology* t);

However, I found a lot of places using “handleTopologyChange” method, e.g. TLineModel, HexahedronFEMForceField, BarycentricMapping, etc. And “handleStateChange” seems still working too.

At the same time, there are also a lot of places using TopologyEngine, e.g. EdgeSetTopologyModifier, HexahedronSetTopologyModifier, etc..

I tried to remove triangles using TriangleSetTopologyModifier, and monitored the “m_enginesList” in TriangleSetTopologyContainer, “m_enginesList” seems to be empty during the removal (I maybe wrong).

What is TopologyEngine for ?
What are “TriangleSetTopologyModifier::propagateTopologicalEngineChanges()”, “TriangleSetTopologyContainer::updateTopologyEngineGraph()” and some other functions related to TopologyEngine for ?

Regards,
Weng Bin

[Weng]

It has been 6 days… no one answer…

Currently, what I know:

(1) TopologyEngine and handleTopologyChange() are both used in SOFA.
(2) TopologyEngine supports: PointData, EdgeData, …, HexahedronData (see TopologyData.h), all these data (variable) will be automatically updated according to the topology changes, no need to handleTopologyChange for them.
for example:
in BarycentricMapping.h : in BarycentricMapperHexahedronSetTopology
topology::PointData< sofa::helper::vector<MappingData> > map;

in the init()

if (this->toTopology)
{
map.createTopologicalEngine(this->toTopology);
map.registerTopologicalData();
}

indicates that map is using TopologyEngine,

(3) All the other situations rely one handleTopologyChange
for example, in TriangleModel.inl: void TTriangleModel<DataTypes>::handleTopologyChange()

If I misunderstood anything, please reply

regards,
Weng Bin

[epernod]

Hi,

yes you are right, the TopologyEngine was a new mechanism to handle topological changes.
This work has not been totally finished, that is why you can find some duplicated mechanisms.

The main idea was to change the previous mechanism that was propagating topological changes through the scene graph by a new one using only the Data graph dependencies.
Thus, each Data will automatically update itself only when his parentData is dirty and propagate the change to his children.

It is very old for me now… so I will need to go deeper in the code if you want a full explaination but basically let’s take the example of the TriangularFEMForcefield.

This FEM store several data/values for each triangle, edge and vertex, through the inner classes:
TriangleInformation, EdgeInformation and VertexInformation

Looking only at the triangles (but it is the same for each topological element), all the information on the triangulation is stored on a single Data:
TriangleData<sofa::helper::vector<TriangleInformation> > triangleInfo;

By default a TriangleData will be set as Child of the Data m_triangles (from the Topology Container) using the line of code:
triangleInfo.registerTopologicalData();

Thus, changing the number of triangles in the topology imply that the child Data triangleInfo is dirty and need an update.
This will be automatically handle by the TopologyEngine if you add a TopologyHandlerto that TriangleData. You need to implement that TopologyHandler. Here it correspond to the class:
class TRQSTriangleHandler : public TopologyDataHandler<Triangle,vector<TriangleInformation> >

and you register it using the line of code:
triangleInfo.createTopologicalEngine(_topology, triangleHandler);

In this Handler you describes all the rules to create/destroy/… the corresponding Data. Look at the method for example:
void TriangularFEMForceField<DataTypes>::TRQSTriangleHandler::applyCreateFunction(

You can see the list of method to overwrite in the file TopologyDataHandler.h The event corresponding to the topological change is automatically handle from the TopologyEngine, it will know which method to call between creation, destruction, swap of elements.

Hope this is clear… at least it just removed a big pile of dust from my brain 🙂

Erik

[Weng]

Hi, Erik

Thanks for your reply.
This is really helpful for anyone working on cutting.

Best regards,
Weng Bin

[Author]

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