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Introduction to Graphics


Introduction to Graphics

To start with graphics programming, Turbo C is a good choice. Even though DOS has its own limitations,  it is having a large number of  useful functions and is easy to program. To implement graphics algorithms,  To give graphical display of statistics, To view signals from any source, we can use C graphics. Here  is  a article to start programming  with  Turbo  C. ‘Run and Learn’ is  our   method.   We  have  used source codes throughout the explanations. Just  execute  them to understand what is happening.

Turbo C has a good collection of graphics libraries. If you know the basics of C, you can easily learn graphics programming. To start programming, let us write a small program that displays a circle on the screen.


/* simple.c
example 1.0
void main()
int gd=DETECT, gm;
initgraph(&gd, &gm, “c:\turboc3\bgi ” );

To run this program, you need graphics.h header file, graphics.lib library file and Graphics driver (BGI file) in the program folder. These files are part of Turbo C package. In all our programs we used 640×480 VGA monitor. So all the programs are according to that specification. You need to make necessary changes to your programs according to your screen resolution. For VGA monitor, graphics driver used is EGAVGA.BGI.

Here, initgraph() function initializes the graphics mode and clears the screen. We will study the difference between text mode and graphics mode in detail latter.

InitGraphInitializes the graphics system.

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

Remarks: To start the graphics system, you must first call initgraph.

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

initgraph also resets all graphics settings (color, palette, current position, viewport, etc.) to their defaults, then resets graphresult to 0.

*graphdriver: Integer that specifies the graphics driver to be used. You can give graphdriver a value using a constant of the graphics drivers enumeration type.

*graphmode : Integer that specifies the initial graphics mode (unless *graphdriver = DETECT). If *graphdriver = DETECT, initgraph sets *graphmode to the highest resolution available for the detected driver. You can give *graphmode a value using a constant of the graphics_modes enumeration type.

pathtodriver : Specifies the directory path where initgraph looks for graphics drivers (*.BGI) first.  If they’re not there, initgraph looks in the current directory.  If pathtodriver is null, the driver files must be in the current directory.  This is also the path settextstyle searches for the stroked character font files (*.CHR).

closegraph() function switches back the screen from graphcs mode to text mode. It clears the screen also. A graphics program should have a closegraph function at the end of graphics. Otherwise DOS screen will not go to text mode after running the program. Here, closegraph() is called after getch() since screen should not clear until user hits a key.

If you have the BGI file in the same folder of your program, you can just leave it as “” only. you need not mention *graphmode if you give *graphdriver as DETECT.

In graphics mode, all the screen co-ordinates are mentioned in terms of pixels. Number of pixels in the screen decides resolution of the screen. In the example 1.0,  circle is drawn with x-coordinate of the center 200, y-coordinate 100 and radius 150 pixels. All the coordinates are mentioned with respect to top-left corner of the screen.


example 1.1
void main()
int gd=DETECT, gm;
int poly[12]={350,450, 350,410, 430,400, 350,350, 300,430, 350,450 };
initgraph(&gd, &gm, “”);
outtextxy(75,170, “Circle”);
outtextxy(240, 170, “Rectangle”);
ellipse(500, 100,0,360, 100,50);
outtextxy(480, 170, “Ellipse”);
sector(150, 400, 30, 300, 100,50);
outtextxy(120, 460, “Sector”);
drawpoly(6, poly);
outtextxy(340, 460, “Polygon”);


CPlusPlus Graphics

Here, circle() function takes x, y coordinates of the circle with respect to left top of the screen and radius of the circle in terms of pixels as arguments. Not that, in graphics, almost all the screen parameters are measured in terms of pixels.

Function outtextxy() displays a string in graphical mode. You can use different fonts, text sizes, alignments, colors and directions of the text that we will study later. Parameters passed are x and y coordinates of the position on the screen where text is to be displayed. There is another function outtext() that displays a text in the current position. Current position is the place where last drawing is ended. These functions are declared as follows:

void far outtextxy(int x, int y, char *text);
void far outtext(char *text);

Circle, arc, pieslice are declared as follows:


*  void far arc(int x, int y, int stangle, int endangle, int radius);
*  void far circle(int x, int y, int radius);
*  void far pieslice(int x, int y, int stangle, int endangle, int radius);


* arc draws a circular arc in the current drawing color.
* circle draws a circle in the current drawing color.
* pieslice draws a pie slice in the current drawing color, then fills it using
the current fill pattern and fill color.


* (x,y): Center point of arc, circlew, or pie slice
* stangle: Start angle in degrees
* endangle: End angle in degrees
* radius: Radius of arc, circle, and pieslice

Here, stangle and endangle are in degrees starting from the +ve x-axis in the polar coordinate system in the anti-clockwise direction. if stangle is 0, endangle is 360, it will draw a full circle. Refer this figure for clear idea: For the details of current color, fill color and fill patterns, refer the sections Lines and Colors.


Another basic shape that we come across is a rectangle. To draw a border, use rectangle with the coordinates of outline, to draw a square use rectangle with same height and width. drawpoly() and fillpoly() are two functions useful to draw any polygons. To use these functions, store coordinates of the shape in an array and pass the address of array as an argument to the function. By looking at the output of the previous program, you can understand what drawpoly is. fillpoly is similar except that it fills in the shape with current fill color.


*   void far rectangle(int left, int top, int right, int bottom);
*   void far drawpoly(int numpoints, int far *polypoints);
*   void far fillpoly(int numpoints, int far *polypoints);


*  Rectangle draws a rectangle in the current line style, thickness, and drawing color.
*  Drawpoly draws a polygon using the current line style and color.
*  Fillpoly draws the outline of a polygon using the current line style and color, then fills the polygon using the current fill pattern and fill color.


*  (left,top) is the upper left corner of the rectangle, and (right,bottom) is its lower right corner.
*  numpoints:  Specifies number of points
*  Polypoints: Points to a sequence of (numpoints x 2) integers. Each pair of integers gives the x and y coordinates of a point on the polygon.

To draw a closed polygon with N points, numpoints should be N+1 and the array polypoints[] should contain 2(N+1) integers with first 2 integers equal to last 2 integers.

Let us study more about shapes latter. Here is some idea about colors. There are 16 colors declared in graphics.h as listed bellow.

BLACK            : 0
BLUE              : 1
GREEN           : 2
CYAN             : 3
RED               : 4
MAGENTA      : 5
BROWN         : 6
LIGHTRED     : 12
YELLOW        : 14
WHITE           : 15

To use these colors, use functions setcolor(), setbkcolor() and setfillstyle(). setcolor() function sets the current drawing color. If we use setcolor(RED); and draw any shape, line or text after that, the drawing will be in red color. You can either use color as defined above or number like setcolor(4);. setbkcolor() sets background color for drawing. Setfillstyle sets fill pattern and fill colors. After calling setfillstyle, if we use functions like floodfill, fillpoly, bar etc, shpes will be filled with fill color and pattern set using setfillstyle. These

function declarations are as follows.

*  void far setfillstyle(int pattern, int color);
*  void far setcolor(int color);
*  void far setbkcolor(int color);


* setfillstyle sets the current fill pattern and fill color.
* setcolor sets the current drawing color to color, which can range from 0 to getmaxcolor.
* setbkcolor sets the background to the color specified by color.

The parameter pattern in setfillstyle is as follows:


Here is an example program with colors, pixels, bar, cleardevice etc. stdlib.h is used for random number generation. We have a function random(no), it returns a random number between 0 an no. The effect is by drawing random radius, random color circles with same center and random pixels. kbhit() function(defined in conio.h) returns a nonzero value when a key is pressed in the keyboard. So, the loop will continue until a key is pressed.


#include “graphics.h”
#include “conio.h”
#include “stdlib.h”
void main()
int gd,gm;
initgraph(&gd, &gm, “”);
bar(50, 50, 590, 430);
setfillstyle(1, 14);
bar(100, 100, 540, 380);
putpixel(random(439)+101, random(279)+101,random(16));