CIGAL Reference Manual, Chapter 1 (Topics): graphics
An important aspect of CIGAL is its ability to do computer graphics. In general, computer graphics involve creating pictures with the computer. Such pictures can be illustrations of real objects, data graphs, bar charts, or original artwork; in short, they can be any drawn visual. Within CIGAL, which can do both graphics and image processing, graphics generally refer to commands and data variables that deal with actually drawing a picture, whereas image processing generally refers to operations that deal with already drawn pictures (see CIGAL(1) for a fuller discussion of this distinction.) Note: The following is applicable to DOS CIGAL only
To do graphics, the first step is to put the computer into “graphics mode”. Normally when you begin a CIGAL session, the program will start up in “text mode”. In this mode, writing and moving text on the screen is very efficient, but it is not well suited for drawing pictures. In graphics mode, you can still write text on the screen (albeit somewhat more slowly) but you can also draw pictures. The difference is that in text mode the screen is broken up into a matrix of character positions, each of which consists of a rectangle of screen dots, and you simply specify which character code to put at each character position, whereas in graphics mode you can read or write each dot on the screen individually.
The IBM PC family of computers supports a variety of different text and graphics modes, depending on which video option your computer contains. For most graphics applications the VGA type of video processor is recommended, and most of the remaining discussion will assume you have VGA color video available. If not, you can still do graphics with CIGAL but without many of the color and high resolution capabilities.
Although CIGAL supports all standard video hardware modes (see SCREEN(1)), with practice some modes are much more useful than others. If you have VGA video you will tend to use:
mode 3 for all text mode operations (80 x 25 characters) mode 17 for 2 color (black/white) drawing (640 x 480 pixels) mode 18 for 16-color drawing (640 x 480 pixels) mode 19 for 256-color drawing and imaging (320 x 200 pixels)
and if you have a Super-VGA monitor you will use
mode ?? for 256-color drawing and imaging (640 x 480 pixels)
Video modes are normally changed automatically depending on which menu commands you select.
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