Structure Modelling

Structure Modelling: Graphical kernal system was adopted first Graphics Standard. Although gks was first designed as a 2-dimensional graphics package PHIGS Programmer hierarchical interactive graphics standard. Structure Concepts: A labeled set of output Primitives in PHIGs is called a Structure. Basic Structure Functions: When we Create a Structure the co-ordinate positions and attribute values specified for the structure are stored as a labeled group in a system structure list called the central structure store. We create a structure with the function Openstructure (id) : The Label for the segment is the positive integer assigned to parameter id. After all primitives and attributes have been listed the end of the structure is signaled with the closestructure Statement. Example: openstructure(6); Setlinetype(lt); Closestructure();

Once he Structure has been created it can be displayed on a selected outputdevice with the function poststructure(ws, id, priority); Where WS is the workstation identifier, id is the structure name and priority as assigned a real value in the range from 0 to 1. To Remove the display of a structure from a particular output device we invoke the function . unpoststructure(ws,id) All structure can be removed from the selected output device with unpostallstructure(ws) Deletestructure(id) for Deleting . Setting Structure attributes. Setinvisibilityfilter( WS,Devcode,invisset,visset) setHighlightingfilter (ws, devcode, highlightset, nohighlightset)

Editing Structure: openstructure(shape) setlinetype(lt); closestructure; The above structure can be edited. Structure list and element pointer: Indexing Setting the edit mode: Seteditmode(mode)(insert,replace); deleting structure element: deleteelement Model Representation:

Input of Graphical data Logical input device classification in terms of the kind of data to be input by device. LOCATOR: a device for specifying a co-ordinate position(x,y) STROKE: a device for specifying a series of co-ordinate positions: STRING: a device for specifying text input. VALUATOR: a device for specifying scalar values. CHOICE: a device for selecting menu options: PICK: a device for selecting picture components:

Interactive Picture Construction Techniques Basic Positioning Methods: Constraints: Grids Gravity field Rubber band methods Dragging Painting and drawing