CashFlow, A Visualization Framework for 3D Flow - Studierstube ...

Software Design3.3. Indirect References & Linking of Nodesduring the scene graph traversal is changed the linking of nodes should change in thesame way.For example in figure 3.4 node A and node B are data storage nodes. Let us assume,that the nodes R, S and T are three different kinds of visualization algorithms that areable to render the data from node A and node B. While traversing the scene graph nodeA is passed first. Afterwards Node R renders the data from node A. The next node intraversal order is the second rendering node S processing the same data from node A.Node B holds different data which is rendered by node T. Using implicit linking enablesthe user to simply exchange node A with node B and obtain a plausible behavior of thevisual result. Now the nodes R and S will render the data from node B and node Twill render the data from node A. The assumption made in this example is, that node Aand node B use the same type of data. The unique key used for that is called a relativeaddress key. The opposite to the relative address key is the absolute address key whichis a unique string.These short example emphasize the possibilities and advantages of a scene graphused for data flow modeling.Figure 3.4: CashFlow: Implicit Linking on Nodes: Node A stores data. Node R visualize the data from nodeA. Node S also renders the data from node A, because no new data node is used in between. Node T finallyrenders the data stored in node B.Figure 3.4 illustrates such a scene graph traversal dependent data flow model. Note,that the traversal order used is depth first search and left before right node order.Each time the scene graph is traversed a traversal state is maintained. The nodes inthe scene graph are visited using a depth first search order and a left before right order.The traversal state stores parameters and references that can be modified by the nodes.These transient parameters only exist during one traversal of the scene graph and arereferred as traversal state elements.While processing the scene graph each node can get access to the traversal stateelements 5 . These elements store all kind of data used for rendering as for example thecurrent color. This is especially useful, because nodes can refer to other nodes holdingcertain pieces of information without being explicitly linked to these nodes. These5 for details on elements see Implementation SoElements.44