Familiarisation with Graphics Devices and Primitives
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Computer graphics devices come in all shapes and sizes: storage tubes, raster devices, vector refresh displays, flat-bed plotters etc., which is why in recent years so much effort has been put into graphics software standards (such as G.K.S. (Hopgood et al., 1983)) as well as into the portability of graphics packages (GINO, CalComp etc.). This book will concentrate on the techniques of modelling and rendering (that is, drawing, colouring, shading etc.) two-dimensional and threedimensional objects, which surprisingly require only a small part of the above systems. Rather than restrict ourselves to one software system, and in order to make this book relevant to as many different graphics devices as possible, we will identify a general model for a graphics device together with a few (nine) elementary routines (primitives) for manipulating that model. From the outset is must be realised that we are using the word ‘primitive’ in the literal sense of describing the basic level at which the programs in this book communicate with graphics devices; the word has different meanings in other graphics environments, such as G.K.S. The FORTRAN 77 programs that follow will use only these primitives for drawing on this basic model (apart from a few very exceptional cases). Since even the most complex programs given in this book interface with the model device through relatively few primitive routines, the graphics package we create is readily portable. All that is needed is for users to write their own device-specific primitives, which relate to their particular graphics device or package! Later in this chapter we give ideas of how such primitives may be written, and in the appendix there are example listings of primitives suitable for some of the more popular graphics devices and standards.
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