Working with nodes

C3DSceneNode are entities linked together hierarchically by the scene.
A node makes a reference to a C3DBaseObject giving it, in particular, a name and a matrix transformation.

So one of the important thing to know is how to create nodes and how to retrieve them using scene traversal.

Get / set node object

Whereas a node can have no object attached to it, this is not recommended unless because such nodes are ignored during traversal unless using NODEPOS_ALLOW_EMPTY_NODES flag.

• C3DSceneNode::GetObject allows to retrieve the C3DBaseObject of the node.
• C3DSceneNode::GetGeomObject return a C3DGeomObject if the node object has one of the OBJECT_GEOM type.
• C3DSceneNode::SetObject allows to attach an object to the node. If the object has to be instantiated, you must have to call C3DSceneNode::CreateObjectInstance before and attach the returned instance.

Creating a node and adding it to the scene

This simple code creates an object group and add it to the scene.

C3DGroup *group = xNew(C3DGroup);
C3DSceneNode *groupNode = xNew(C3DSceneNode);
groupNode->SetObject(group);
groupNode->SetName("My group");
scene->AddNode(NULL, groupNode); // node is a child of the scene root
 
C3DCurve *curve = xNew(C3DCurve);
C3DPointList *points = xNew(C3DPointList);
C3DPoint *pt;
 
points->SetSize(10);
for (int j=0; j<10; j++)
{
    pt = &(*points)[j];
    pt->x = j;
    pt->y = j*2.0f;
    pt->z = j*3.0f;
}
 
curve->SetPointList(points);
 
C3DSceneNode *curveNode = xNew(C3DSceneNode);
curveNode->SetObject(curve);
curveNode->SetName("My curve");
 
scene->AddNode(groupNode, curveNode); // Curve is child of "My group"

Instantiation

Several nodes can reference the same C3DBaseObject. This means that the scene contains the same object several times at different position. Instantiation is a simple way to save memory usage.
C3DSceneNode::IsObjectIntanciated allows to know if the node object is referenced several times, whereas C3DSceneNode::DeleteObjectInstanciation attach a copy of the instantiated object to the node (the object instantiation count decrease by one).

Transformations

Transformations are associated to node using KEYFRAME_MATRIX (C3DMatrixKey) or a combination of KEYFRAME_ROT (C3DRotateKey), KEYFRAME_TRANS (C3DTranslateKey), KEYFRAME_SCALE (C3DScaleKey), KEYFRAME_PIVOT (C3DVectorKey).
The transformation associated to the node are the local transformation. It can be retrieved using C3DSceneNode::GetObjectLocalTM or C3DSceneNode::GetNodeLocalTM.
You can retrieve a world transformation matrix using C3DSceneNode::GetNodeTM which accumulates matrices along the hierarchy. Finally you can modify the node transformation using C3DSceneNode::SetObjectLocalTM.

Transformation are defined at a given time, which means that you'll have to define the time in most of the method. C3DScene::GetCurrentTime returns the current time.
It is possible to remove any transformation using C3DSceneNode::ConvertToGlobalCoordinates.

C3DPointList *points = object->GetPointList();
if (points)
{
    C4x4Matrix matrix;
    node->GetNodeTM(scene->GetCurrentTime(), matrix);
 
    int i, size = points->SetSize(10);
    for (int j=0; j<10; j++)
    {
        pt = &(*points)[j];
        pt=matrix*pt; // pt has now world coordinates
    }
}