Def. A scene graph is a n-ary tree where  each leaf is  either a geometrical object or a property (sometimes);  the structure reflects a physical relation between the objects.

Example:

Properties in scene graphs can be either physical properties (color, surface properties, transparency, etc.) or geometrical properties, i.e. transformations. While descending in the tree: physical properties are inherited, unless redefined, transformations are composed .

• Going from a parent to a child node:

glPushMatrix();

• Going from a child back to the parent:

 glPopMatrix(); 

• OpenInventor, DataViewer, VTK, etc.
• Each type of node in the tree is represented by a class.
• All of them are derived from a base class, Object.
• Each of them implements a function draw with the same name and list of parameters.
• The draw is defined as an abstract function in the Object class and is virtual in general.
• The base class also specifies some properties that can be applied to any node in the graph (color, rotation, etc.)

• The leaf nodes are geometrical classes.
• A class contains a set of features that describe dimensions, spatial position, and special properties of the geometrical object. For example, for a sphere, it would contain the radius and the center.
• The draw function for a leaf node generates a list of OpenGL commands specific to that object and using the properties defined by the node.

• Non-terminal nodes in the graph are usually known as containers.
• They contain at least an array of Object pointers that will be links to the children.
• The actual objects to which these will point are either other containers, or geometrical objects.
• The draw function for the containers applies the locally defined properties and transformations and calls the draw function for each child.
• Since the draw function is virtual, the container doesn’t have to know the class of each child.

• Base class: DVobject.
• Geometrical classes: DVlines, DVtriangles, DVspheres, etc.
• In DV, geometrical objects are designed to contain large amounts of data for easy integration with numerical applications..
• A whole surface could fit in just 1 DVtriangles object.

• They are all derived from DVcontainerbase.
• Simple containers draw all of their children.
• Animation containers: selection (flip-book) and interpolation (key-frame).
• Selection containers call the draw function of just 1 child at a time based on a frame number.
• Interpolation containers call the draw function for all of the children after applying a transformation based on the frame number and on an array of transformations defined for a set of key frames.

Useful for objects that will be drawn more than once.

Start a new display list:
glNewList(GLuint name, GLenum mode);

End the current display list
void glEndList();

mode can be
 

GL_COMPILE	The commands in the list will not be executed as they are stored in the display list.
GL_COMPILE_AND_EXECUTE	The commands will be executed as they are stored in the display list.

Execute a display list:
void glCallList(GLuint name);