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GRAPHICS.
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Turbo C provides a separate library of over 70 graphics functions, ranging
from high-level calls (like setviewport, bar3d and drawpoly) to bit-oriented
functions (like getimage and putimage). These functions are in the library
file GRAPHICS.LIB and they are prototyped in the header file GRAPHIC.H,
which must be included in every program that uses graphics. As well as
these two files, the graphics package includes Borland graphics device
drivers (*.BGI files) and stroked character fonts (*.CHR files).
In order to use the graphics functions with TC.EXE it is necessary to toggle
Options/Linker/Graphics library to On. Thus when the call to 'Make program'
is made, the linker will automatically link in the Turbo C graphics library.
When using the command line version TCC.EXE then GRAPHICS.LIB must be
included on the command line, as in the example:
tcc myprog graphics.lib
The graphics functions can be divided into the following seven categories:
Graphics system control
Drawing and filling
Manipulating screen and viewports
Text output
Color control
Error handling
State query
The graphics system control functions are listed on page 228 of the User's
Guide and include the essential functions:
detectgraph checks hardware for correct graphics driver to use
(CGA, EGA, VGA, etc.) and recommends a graph mode.
initgraph initializes the graphics system and changes to graph
mode.
closegraph shuts down the graphics system.
The program GRAPHICS.C illustrates the use of these functions and includes
the folowing lines:
#include <graphics.h>
...
int graphdriver, graphmode, grapherror;
...
detectgraph(&graphdriver, &graphmode);
...
initgraph(&graphdriver, &graphmode, "");
...
closegraph();
The function closegraph() unloads the driver from memory and restores the
original video mode by means of another control function restorecrtmode().
Full details of all these functions can be found in Chapter 2 of the
Reference Guide, arranged in alphabetical order.
The drawing and filling functions are listed on page 231 of the User's
Guide and include:
circle draws a circle
line draws a line from (x0,y0) to (x1,y1)
moveto moves the current position (CP) to (x,y)
rectangle draws a rectangle
bar draws and fills a bar
fillpoly draws and fills a polygon
Thus it is possible to draw colored lines, arcs, circles, ellipses,
rectangles, pieslices, 2- and 3-dimensional bars, polygon, and regular or
irregular shapes based on combinations of these.
A typical drawing command from the program GRAPHICS.C is
line(69,MaxY-30,MaxX-70,MaxY-30); /* draws x axis for -5<x<+5 */
The functions for manipulating the screen and viewport are listed on page
233 of the User's Guide and include:
cleardevice clears the screen (active page)
setviewport sets the current output viewport for graphics
output
putpixel plots a pixel at (x,y)
The use of one of these commands in the program GRAPHICS.C is
setviewport(0,0,MaxX,MaxY,1);
where the parameters are left, top, right, bottom and clip. The last
parameter, if non-zero, indicates that the drawings are truncated at the
current viewport boundaries. Full details are given on page 332 of the
Reference Guide.
The functions for text output in graphics mode are listed on page 234 of the
User's Guide and include:
outtextxy sends a string to the screen at the position
specified by the first two parameters (x,y,string)
settextjustify sets text justification values used by outextxy
The function settextjustify is fully defined on pages 324-5 of the Reference
Guide. The two parameters refer to the horizontal and vertical
justification around the current position (CP). These functions are used in
the program GRAPHICS.C as follows:
...
settextjustify( CENTRE_TEXT, CENTRE_TEXT );
outtextxy( OX, 10, "Graph of y = x^2 + 5" );
...
The color control functions are shown on page 236 of the User's Guide and
include:
getbkcolor returns the current background color
getcolor returns the current drawing color
setbkcolor sets the current background color
setcolor sets the current drawing color
The single parameter for both setcolor and setbkcolor is an integer value,
ranging from 0 to 15, as shown on page 238 of the User's Guide or page 313
of the Reference Guide for both CGA and EGA modes. VGA mode is similar to
EGA but has higher resolution. None of these functions are used in the
program GRAPHICS.C so the default white on black is used.
The functions for error handling in graphics mode are given on page 240 of
the User's Guide and are as follows:
grapherrormsg returns an error message string for the specified
error code.
graphresult returns an error code for the last graphics
operation that encountered a problem.
Error return codes are listed in the Guide, 0 indicates no error, whilst a
range of negative integers to -18 indicate the various errors. The
demonstration program GRAPHICS.C uses these function as follows:
grapherror = graphresult();
if (grapherror < 0 )
{
printf("Initgraph error: %s \n",grapherrormsg(graphmode));
exit(1)
}
The state query functions are listed on page 241 of the User's Guide and
include:
getaspectratio returns the aspect ratio of the graphics screen
getcolor returns the current drawing color
getmaxx returns the current x resolution
getmaxy returns the current y resolution
Two of these functions are used in the program GRAPHICS.C in order to
evaluate the parameters MaxX and MaxY to be used in the function call
setviewport, as shown above. These function calls are as follows:
MaxX = getmaxx();
MaxY = getmaxy();
The program GRAPHICS.C makes use of several other functions taken from the
Shareware Marketing diskette called 'Turbo C Utilities' in order to obtain
hardcopy in either normal (portrait) or landscape mode. These are shown in
the section commented as /* Function prototypes */.
This demonstration program draws the axes and the parabolic graph for the
function y = x^2 + 5 in the range -5 < x < +5. The reader is invited to
complete the graphical representation by marking and labelling the axes at
unit intervals on the x axis and intervals of 5 units on the y axis. This
will involve use of the 'line' function for the axis marks and the
'outtextxy' function for the values.
Those users with experience of Turbo Pascal will observe that the Turbo C
graphics functions are similar to the graphics procedures and functions of
Turbo Pascal.
The essential functions to initialize the graphics system ( detectgraph and
initgraph ) must always be included in a graphics program and at the same
time the appropriate *.BGI file must be available on the default drive.
Thus the file CGA.BGI must be available for a CGA monitor (320 x 200) or
EGAVGA.BGI for a VGA display (640 x 480 pixels).