C Program to draw a line

Graphics in C - Draw a Simple Line

Computer graphics is a very interesting and important area in any computer language. C is a powerful language as far as graphics are concerned. There are so many ready-made graphics functions available in the C computer language. Let us explore one by one through programs.

Here I assume that you have some basic knowledge of C computer language at your disposal and you have Turbo C installed on your computer.

Here is a simple program given below:

#include<graphics.h>

void main()

{

       int gd=DETECT, gm;

       initgraph(&gd, &gm, "c:\\tc\\bgi");

       line(200, 200, 400, 200);

       getch();

       closegraph();

       restorecrtmode();

}

Let us understand the program line by line:

The first line #include<graphics.h>  tells the compiler to include the header file “graphics.h”. To draw anything on the screen we need a header file ‘graphics.h’ and a library file ‘graphics.lib’. This header file contains the definition of all the graphics functions and constants. The library file contains graphics functions.

To create graphics we need to change our computer from text mode to graphics mode. For this we have to call the function initgraph().

Declaration:

void far initgraph(int far *graphdriver, int far *graphmode, char far *pathtodriver);

Function initgraph() initializes the graphics system by loading a graphics driver from disk then putting the system into graphics mode.

Function initgraph() also resets all graphic settings (color, palette, current position, viewport, etc,) to their defaults, and then returns 0.

Two variables of integer type, named 'gd' and 'gm', have been defined. 'gd 'refers to graphics driver and 'gm' refers to graphics mode. Graphics drivers are the small programs, which communicate directly to the hardware. Turbo C has some certain graphics drivers. These drivers are files with the extension name ‘bgi’. On the basis of adapter, appropriate bgi file is selected.  'gd' has been assigned the value 'DETECT '.  'DETECT' is a macro whose responsibility is to detect appropriate 'bgi' file. Because of this, initgrapgh()  figures out the appropriate 'bgi' file.  Then this file is loaded into memory.

Function initgraph()  has been called to assign the values to 'gm' and 'gd'. This function figures out the best value i.e. best resolution and puts the value in the variable 'gm'. This function also figures out the best 'bgi' file and puts the value in 'gd'. 'bgi' files are generally found in 'c' drive’s 'tc' directory. So the path is given ‘c:\tc\bgi’. If your computer has different path, change this accordingly.

Since in the declaration of function initgraph(), arguments are of pointer type, that's why we have passed the addresses of 'gd' and 'gm'.

When switched to graphics mode some changes occur. One is, our cursor disappears from the screen. Other is, screen is now measured by the coordinate system, in which the top left corner is (0, 0) and the values are increased vertically and horizontally.  Every point on the screen is denoted by the (x, y). First value is the x-axis, which goes horizontally across, second value is y-axis, which goes vertically downward.

Function line() draws a line between two given points.

Declaration:

void far line(int x1, int y1, int x2, int y2);

Function line() draws a line from (x1, y1) to (x2, y2) using the current color, line styles, and thickness. So line(200, 200, 400, 200) draws a line from point (200, 200) to point (400, 200).

Function getch() gets a character from keyboard but does not echo to the screen. I have used this function to hold the output; otherwise you won’t be able to see the output.

Function closegraph() shuts down the graphics system, frees all memory allocated by the graphics system. It then restores the screen to the mode it was in before calling function initgraph().

Declaration:

void far closegraph(void);

Function restorecrtmode() restores the original video mode detected by function initgraph().

Declaration:

void far restorecrtmode(void);

So this simple program is well explained now.  Although it does not do anything significant, but it is a building block for graphics programming in C computer language.

OUTPUT:

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