Computer graphics is a wonderful invention in the field of Computers. It is used in diverse areas such as displaying the results of engineering and scientific computations and visualization, producing television commercials and feature films, simulation and analysis of real world problems, computer aided design, graphical user interfaces that increases the communication bandwidth between humans and machines, etc. The art of creating pictures with a computer has got numerous applications, that it is of great importance to explore the intrinsics of the world of computer graphics. The advent of CRTs brought about a major change in the world of computers. No longer do we have to depend upon the awkward and time consuming punching cards or the cryptic commands.
Computer graphics is application oriented. The first application was Ivan Sutherland's Sketchpad which allowed user to draw on the screen. Though it may look trivial, it is a major breakthrough in the graphical field which proved to the world that computers could be used interactively to produce graphic output on a CRT display. Then came the paint systems which made the basic communication between human and computer more pictorial. Word processing, Desktop publishing, Business graphics (like analytical charts graphs and other displays of information which made the message forceful and emphatic), Computer-Aided design which allows speedy and easy design of buildings, mechanical systems, floor plans or electronic circuit boards, simulation of real world problems which provides a safe learning environment and major savings, gained public attention. Computer games which contributed considerably to the popularity of computer graphics, followed suite.
The evolution of computer graphics has been quite rapid in the past 10 - 15 years with improved hardware and software technologies. It wouldn't be a surprise, if in the future, virtual reality workstations and software which are highly interactive and user friendly, becomes the integral part of any computer, just like motors are in any hardware machine.
A primitive is a graphics object that is essential for the creation or construction of complex images. Fortunately, graphics is constructed from three basic elements, as opposed to the great variety of graphics applications. The most basic of these elmental structures is the pixel, short for picture element.
A pixel is a point of light. It is just one tiny dot on the raster displays. Though it has no structure, it is definitely a building block and hence it can be considered as the graphics primitive.
The resolution of CRT is related to the dot size, the diameter of a single dot. A resolution of 100 dots lines/inch implies a dot size of 0.01 inch. However, in reality, pixels are more elliptic than circle. The shape of a pixel purely depends upon the characteristics of the visual display unit. The ratio of the distance between the centres of two adjacent horizontal pixels to that of the vertical ones is called the pixel ratio.
For example, if 100-pixel lines in x and y measure 6cm and 8cm respectively, then
Pixel ratio should be considered in line-generating algorithms.
Line, especially straight lines, constitute an important building block of computer images. For example, Line is the basic building block of Line graphs, bar and pie charts, two and three-dimensional graphs of mathematical functions, engineering drawings and architectural plans.
In computer graphics, straight line is so basic in creating images that we call it a graphics primitive. Straight lines can be developed in two different ways. A structural method determines which pixels should be set before drawing the line; a conditional method tests certain conditions to find which pixel should be set next.
A polygon, even though generally constructed from straight lines, is an important graphics primitive. So often we want to handle polygon as a single entity, as images of objects from the real world consist in large, part of polygons.
A polygon is a closed area of image bounded by straight or curved lines and filled with one solid color. Since images are two dimensional, a polygon is a closed planar figure.
Implementing a polygon as a graphics primitive is natural and helpful. We can define polygon as an image which consists of a finite ordered set of straight boundaries called edges.
Alternately, the polygon can be defined by an ordered
sequence of vertices, the corners of the polygon.
The edges of the polygon are then obtained by traversing the vertices in the given order; The edge list is sufficient for wireframe drawings. Two consecutive vertices define one edge. We close the polygon by connecting the last vertex to the first. Facelist is required inorder to fill the polygon.
We can decompose a scene from real world into a collection of polygons of simple shapes. For example, a simple house can be constructed with a square and a rectangle. However, neither straight lines nor polygons precisely describe a real world scene; It is only an approximation of the scene we can get; such scenes actually seem to be of fractal nature.
The graphics pipeline specifies a series of steps needed to display data on an output device. The steps vary depending on the needs of the application. The application may be realistic, fast, aesthetic or informatic.
However, the graphics Pipeline has three major components viz. the application program which stores into and restores from the application data structure and sends graphics command to the graphics system.