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Computer Graphics- SCC 342 Chapter 3: Computer Graphics Software Dr. Doaa Hegazy

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Two broad categories: – Special purpose packages (e.g. CAD systems and painting programs) – General programming packages (e.g. Graphics Library (GL), OpenGL, Virtual Reality Modeling Language (VRML), Java2D, Java3D Computer Graphics Application Programming Interface (CG API)

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3.1 Coordinate Representations General graphics packages require geometric descriptions to be specified in a standard, right handed, Cartesian-coordinate reference frame The right-handed Cartesian coordinate system indicating the coordinate plane Images source:http://en.wikipedia.org/wiki/Cartesian_coordinate_system

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3.1 Coordinate Representations

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Modeling Coordinates (local or master coordinates) World coordinates Viewing coordinates Projection coordinates Normalized Coordinates Device coordinates

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3.2 Graphics Functions The routines in graphics packages cab be classified as functions for: – Graphics output primitives: building block for any picture (lines, circles etc.) – Attribute: properties of output primitives – Geometric transformations: change size, scale and orientation of output primitives – Modeling transformations: modeling complex objects

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3.2 Graphics Functions The routines in graphics packages cab be classified as functions for: – Viewing transformations: select view of the scene, type of projection to be used, location on the display screen – Input functions: control the flow of data from interactive input devices – Control operations: housekeeping functions such as clearing screen area or initialize parameters

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3.3 Software Standards Primary goal of standardizing: Portability Graphical kernel system (GKS) 1984: the first graphics SW standard – adopted by International Standard Organization (ISO) and ANSI Programmer’s Hierarchical Interactive Graphics Systems (PHIGS): the second graphics SW standard – increased capabilities for hierarchical modeling

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3.3 Software Standards Graphics work stations from Silicon Graphics Inc. (SCI): became increasingly popular with the development of GKS and PHIGS Graphics Library (GL): set of routines came with the graphics work stations OpenGL: developed in the early 1990s as a HW independent version of GL

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