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Nodes and Groups
Lee Young Gun
Open Inventor

2. Content The Scene Database & Scene Graphs Types of Nodes & Groups
Shared Instancing of Nodes & Path
Fields within a Node
Ignore flag and Override Flag
References and Deletion
Node Types & Naming Nodes
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3. The Scene Database & Scene Graphs
Consist of information scene
Using of SoDB class
Contain several scene graphs
Two basic operation
SoDB :: init()
Read function : read from a file into the scene database
scene graph
Consist of one or more node, represent a geometry, property or grouping object
Inventor Database
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4. Type of Nodes & Groups - 1 Node
Type of Nodes & Groups - 1
Node
The fundamental element of a scene graph
Contain the data and methods
If create a node, insert into a database
Three basic categories
Shape nodes : 3D geometric objects
Property nodes : appearance and characteristics
Group nodes : collect nodes into graphs
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Open Inventor

5. Type of Nodes & Groups - 2 Create Node Contents of Node Action of Node
Type of Nodes & Groups - 2
Create Node
SoSphere * headSphere = new SoSphere;
Contents of Node
compose a set of data element, called fields
ex) SoPointLight : intensity, color, location, on
Action of Node
create action class
SoGLRenderAction, SoGetBoundingBoxAction
traverse the graph by rules (top->bottom, left->right)
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Open Inventor

6. Type of Nodes & Groups - 3 Basic category of Node Shape node
Represent 3D geometric objects
Cube, cone, sphere, texture etc.
Property node
Represent appearance and characteristics
Surface material, drawing style, geometric transformation
Replace the values in a corresponding elements
Group node
A container for collecting child objects
Collect property, shape, other group node
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7. Type of Nodes & Groups - 4 Groups
First create a group, has no children node
Base class of group : SoGroup
By using the method of addChild, attach the group to nodes
ex)
SoGroup * head = new SoGroup
head->addChild(myXform);
head->addChild(bronze);
head->addChild(headSphere);
Ordering of children :
from left to right
Simple Group
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8. Type of Nodes & Groups - 5 Indexing of child Important ordering
when the child insert, each child node is indexed
first node : index of 0, second node : index of 1
insert method : insertChild(SoNode *child, int newIndex)
insert a child node into a group at the new location by newIndex
ex : body->insertChild(wireStyle, 1);
Important ordering
The property of other node is inherited by the property of root node
Combining Group
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9. Type of Nodes & Groups - 6 Subclass of SoGroup SoSeperator
To isolate the effects of nodes in a group
Before traversing its children, saves the current traversal state
Restore the previous traversal state
No effect anything above or right node in the graph
Separator Groups
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10. Type of Nodes & Groups - 7 Other subclass of SoGroup SoSwitch
Visit only one of its children
Contain one filed, is used whichChild
SoSwitch * s = new SoSwitch;
s->addChild(a); s->addChild(b); s->addChild(d); s->whichChild =2;
Default value : SO_WITCH_NONE(no visiting child node)
SoLevelOfDetail
Specify the same object with varying levels of detail
Useful for applications requiring the fastest rendering possible
Contain one field : screenArea(SoMFFloat)
SoSelection
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11. Type of Nodes & Groups - 8 Scene Graph with Level-of-Detail Node
Different Levels of Detail for an object
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12. Shared Instancing of Nodes & Path - 1
Sharing instancing
A single node has more than one parent
Path
Use to isolate particular objects in the scene graph
If want to refer to the particular node, must be represented by the path, starting at the root node
All action that can be performed on a node can be performed on a path
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13. Shared Instancing of Nodes & Path - 2
Example of Sharing instancing & path
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14. Example of Inventor
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15. Fields within a Node - 1 Field value
Property value of node
As creating node, set to predefine values
Ex)
SoDrawStyle * d = new SoDrawStyle;
d->style.setvalue(SoDrawStyle::LINES);
d->lineWidth.setvalue(3);
d->linePattern.setvalue(0xf0f0);
Single value vs. Multiple value field
Single value field
To have one value of a given type
Class used the letters ‘SF’ : SoSFBool
Multiple value field
To contain an array of values
Class used the letters ‘MF’ : SoMFVec3f
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16. Fields within a Node - 2 Single value field Multiple value field
Setting and Getting value
Setting value
Using method is called setValue()
cam->height.setValue(1.); or cam->height = 1.;
Getting value
Using method is called getValue()
Float result = cam->height.getValue();
Multiple value field
nodeName->fieldName.setValues(starting index,number of values, pointer to array of values);
SoMaterial * mtl; float vals[3];
vals[0] = 0.2; vals[1] = 0.5; vals[2] = 0.9;
mtl->transparency.setValues(0, 3, vals);
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17. Ignore flag and Override Flag
Ignore Flag Methods
Every field has an Ignore flag
Use the setIgnored() method to set or reset the Ignore flag
When Flag is set, the fields is disregarded
Bronze->specularColor.setIgnored(true); // ignore field
Override Flag
Every node has an Override flag
When Flag is set, any nodes of the same type encountered later in the graph are ignore
setOverride() : set and reset the Override flag
isOverride() : return the state of the Override flag
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18. References and Deletion - 1
Reference counting
The number of references made to that node within the database
By calling ref(), unref(), control the reference count
Adds node B to node A : B’s counter = 1
Node C : add to two different parent group
C’s counter = 2
root->ref() : be not referenced being a child
Referencing a node in a path
Incremental the node’s reference count
Incremental the
Reference counts
Reference counts
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19. References and Deletion - 2
Node deletion
Use a reference-counting mechanism
Remove a reference node and a child
Decrements the reference count
If node’s reference count is 0
Delete from the database
Order of decrement
P  0
Q  0
S  1
R  0
S  0
When a group is deleted, all child are removed
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20. References and Deletion - 3
Summary of References and Deletion
Increments Reference Count by 1
Decrements Reference Count by 1
Adding a node as a child of another node increments child’s reference count
Removing a node as a child of another node
Adding a node to a path
Removing a node from a path
Applying an action to a node or path increments reference count of all nodes that are traversed
When traversal for the action finishes, all nodes that were traversed are unreferenced
Adding a node to an SoNodeList node
Removing a node from an SoNodeList
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21. Node Types and Naming Nodes
For runtime type-checking through the SoType class
getTypeId() : obtain the SoType for that instance
getParent() : to find the parent class pf a type
CreateInstance() : to create an instance of a particular type
getName() : to obtain an SbName for the class type
Naming Nodes
Assign a name to a node, path or engine and then search for the object by name
Useful way of identifying objects
Apply to Writing to file or reading from file
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