Index-dependent objects in combination with SofaCarving

[ScheiklP]

Hi,
I have a scene with a triangle mesh whose corners are fixed by a RestShapeSpringsForceField (through indices).

If I delete triangles through the SofaCarving plugin (CarvingManager + CarvingSurface + CarvingTool), the size of the MechanicalObject changes and the RestShapeSpringsForceField crashes because the indices are no longer valid.
The same happens if I delete elements through the MouseManager.

[ERROR]   [RestShapeSpringsForceField(RestShapeSpringsForceField)] Out of Bounds m_indices detected. ForceField is not activated.
[ERROR]   [RestShapeSpringsForceField(RestShapeSpringsForceField)] The dimension of the source and the targeted points are different 

Does anyone have an idea on how I could keep the indices valid?

The scene graph is basically the same as https://github.com/sofa-framework/sofa/blob/master/examples/Demos/TriangleSurfaceCutting.scn, but with a CarvingTool like in https://github.com/sofa-framework/sofa/blob/master/applications/plugins/SofaCarving/examples/CarvingTool.scn

Cheers,
Paul

[hugtalbot]

Hi @ScheiklP

Interesting question! I am not using myself topological changes extensively. @epernod how do you handle such id changes on your end?

[hugtalbot]

Further to a discussion with @epernod, he reminded me that such data (automatically updated with the topological changes) should be TopologyData. Erik presented this API in the STC#13 (see slide 3)
In your case, this means that the Data< type::vector< sofa::Index > > d_points data field of the RestShapeSpringsForceField should be defined as sofa::core::topology::TopologySubsetIndices (like in the FixedConstraint)

We could make it as an issue, instead.

[epernod]

Hi,

yes this is a bug, the RestShapeSpringsForceField should use a TopologySubsetIndices for its indices vector instead of Data< type::vector< sofa::Index > >. This special Data follow topological changes and update itself when element are removed.

See for example how FixedConstraint is managing its fixed indices:

sofa/Sofa/Component/Constraint/Projective/src/sofa/component/constraint/projective/FixedConstraint.inl

Lines 112 to 113 in 471a3df

	// Initialize topological changes support
	d_indices.createTopologyHandler(_topology);

Can you do the changes?
Otherwise, if you have a simple scene to test I could have a look.

[ScheiklP]

Hi @hugtalbot and @epernod ,
Ah, I see, thanks for the tip!

I tried to make the changes (compiles and runs), but the indices are not updated.
master...ScheiklP:spring_forcefield_indices
The scene I used for testing is

<?xml version="1.0"?>
<Node name="root" dt="0.05" showBoundingTree="0" gravity="0 -9 1">
    <RequiredPlugin name="Sofa.Component.Collision.Detection.Algorithm"/> <!-- Needed to use components [BVHNarrowPhase BruteForceBroadPhase DefaultPipeline] -->
    <RequiredPlugin name="Sofa.Component.Collision.Detection.Intersection"/> <!-- Needed to use components [MinProximityIntersection] -->
    <RequiredPlugin name="Sofa.Component.Collision.Geometry"/> <!-- Needed to use components [TriangleCollisionModel] -->
    <RequiredPlugin name="Sofa.Component.Collision.Response.Contact"/> <!-- Needed to use components [DefaultContactManager] -->
    <RequiredPlugin name="Sofa.Component.Constraint.Projective"/> <!-- Needed to use components [FixedConstraint] -->
    <RequiredPlugin name="Sofa.Component.IO.Mesh"/> <!-- Needed to use components [MeshOBJLoader] -->
    <RequiredPlugin name="Sofa.Component.LinearSolver.Iterative"/> <!-- Needed to use components [CGLinearSolver] -->
    <RequiredPlugin name="Sofa.Component.Mapping.Linear"/> <!-- Needed to use components [IdentityMapping] -->
    <RequiredPlugin name="Sofa.Component.Mass"/> <!-- Needed to use components [DiagonalMass] -->
    <RequiredPlugin name="Sofa.Component.ODESolver.Backward"/> <!-- Needed to use components [EulerImplicitSolver] -->
    <RequiredPlugin name="Sofa.Component.SolidMechanics.FEM.Elastic"/> <!-- Needed to use components [TriangularFEMForceField] -->
    <RequiredPlugin name="Sofa.Component.SolidMechanics.Spring"/> <!-- Needed to use components [TriangularBendingSprings] -->
    <RequiredPlugin name="Sofa.Component.StateContainer"/> <!-- Needed to use components [MechanicalObject] -->
    <RequiredPlugin name="Sofa.Component.Topology.Container.Dynamic"/> <!-- Needed to use components [TriangleSetGeometryAlgorithms TriangleSetTopologyContainer TriangleSetTopologyModifier] -->
    <RequiredPlugin name="Sofa.Component.Visual"/> <!-- Needed to use components [VisualStyle] -->
    <RequiredPlugin name="Sofa.GL.Component.Rendering3D"/> <!-- Needed to use components [OglModel] -->

    <VisualStyle displayFlags="showVisual showBehaviorModels" />
    <DefaultPipeline verbose="0" />
    <BruteForceBroadPhase/>
    <BVHNarrowPhase/>
    <DefaultContactManager response="PenalityContactForceField" />
    <MinProximityIntersection name="Proximity" alarmDistance="0.8" contactDistance="0.5" />
    <Node name="Object1">
        <EulerImplicitSolver name="cg_odesolver" printLog="false"  rayleighStiffness="0.1" rayleighMass="0.1" />
        <CGLinearSolver iterations="25" name="linear solver" tolerance="1.0e-9" threshold="1.0e-9" />
        <MechanicalObject name="ms" template="Rigid3d" position="0 0 0 0 0 0 0 1" showObject="false"/>
        <SphereCollisionModel radius="0.01" color="0 1 0 1" />  
    </Node> 
    <Node name="SquareGravity">
        <EulerImplicitSolver name="cg_odesolver" printLog="false"  rayleighStiffness="0.1" rayleighMass="0.1" />
        <CGLinearSolver iterations="25" name="linear solver" tolerance="1.0e-9" threshold="1.0e-9" />
        <MeshOBJLoader name="meshLoader" filename="mesh/square_2594_triangles.obj" scale="10" createSubelements="true" />
        <TriangleSetTopologyContainer  name="Container" src="@meshLoader"/>
        <TriangleSetTopologyModifier   name="Modifier" />
        <TriangleSetGeometryAlgorithms name="GeomAlgo" template="Vec3d" />
        <MechanicalObject name="Mo"/>
        <DiagonalMass massDensity="0.08" />
        <FixedConstraint indices="617 618 57 1301 1302 49" />
        <TriangularFEMForceField name="FEM" youngModulus="60" poissonRatio="0.3" method="large" />
        <TriangularBendingSprings name="FEM-Bend" stiffness="300" damping="1.0" />
        <RestShapeSpringsForceField stiffness="11" angularStiffness="11" external_rest_shape="@../Object1/ms" points="1363" external_points="0" drawSpring="true" springColor="1 1 1 1" recomputeIndices="1" />
        <TriangleCollisionModel />
        <Node >
            <OglModel name="Visual" texcoords="@../meshLoader.texcoords" texturename="textures/colorMap.png" />
            <IdentityMapping input="@.." output="@Visual" />
        </Node>
    </Node>
</Node>

I guess the recomputeIndices() is not triggered correctly?

[hugtalbot]

take a look in the slides I linked, you have the explanation regarding what is needed with TopologySubsetIndices
namely d_indices.createTopologyHandler(_topology);

[ScheiklP]

Ah, I see, thanks! I'll give it a try later. :)

[ScheiklP]

Ok, done and tested. :)
The indices now change correctly.

But I could not find the WriteAccessor<Data<SetIndexArray > > indices = d_indices; part in FixedConstraint.
Seems to work anyway. :D

I also took the liberty of changing up a few loops, so that .getValue() is not called repeatedly in the loop.
master...ScheiklP:spring_forcefield_indices#diff-5a3bd73eff0b61df2084176f079f61c71ef29f844cd04f675d86e411a091a923R204

[hugtalbot]

could be worth PRing @ScheiklP would you agree?