# Bresenham’s Line Drawing Algorithm

8 months ago
Computer Graphics

Bresenham’s line algorithm is an algorithm which determines which order to form a close approximation to a straight line between two given points. Write a C program for determining pixel activation list between two given points in order to draw line segment using bresenham’s Line drawing algorithm?

Aim: To implement Bresenham’s line drawing algorithm for drawing a line segment between two

given endpoints A (x1, y2) and B(x2, y2).

### Description:

Basic Concept:

• Move across the x axis in unit intervals and at each step choose between two different y coordinates • For example, from position (2, 3) we have to choose between (3, 3) and (3, 4). We would like the point that is closer to the original line
• So we have to take decision to choose next So next pixels are selected based on the value of decision parameter p. The equations are given in below algorithm.

### Algorithm:

BRESENHAM’S LINE DRAWING ALGORITHM

1. Input the two line end-points, storing the left end-point in (x0, y0)
2. Plot the point (x0, y0)
3. Calculate the constants Δx, Δy, 2Δy, and (2Δy - x) and get the first value for the decision parameter as:

p     = 2 D y - D x

1. At each xk along the line, starting at k = 0, perform the following If pk < 0, the next point to plot is (xk+1, yk ) and:

p k + 1 =p    + 2 D y

Otherwise, the next point to plot is (xk+1, yk+1) and:

p k + 1 =p k   + 2 D y - 2 D x

5. Repeat step 4 (Δx – 1) times

NOTE: The algorithm and derivation above assumes slopes are less than 1. For other slopes we need to adjust the algorithm slight

### Program:

#include<stdio.h>

#include<conio.h>

#include<graphics.h>

void main()

{

int x,y,x1,y1,x2,y2,p,dx,dy;

int gd=DETECT,gm;

initgraph(&gd,&gm,"C:\\TurboC3\\BGI");

printf("\nEnter the x-coordinate of the first point ::"); scanf("%d",&x1);

printf("\nEnter the y-coordinate of the first point ::"); scanf("%d",&y1);

printf("\nEnter the x-coordinate of the second point ::"); scanf("%d",&x2);

printf("\nEnter the y-coordinate of the second point ::"); scanf("%d",&y2);

x=x1; y=y1; dx=x2-x1; dy=y2-y1;

putpixel(x,y,2);

p=(2*dy-dx); while(x<=x2)

{

if(p<0)

{

}

else

{

x=x+1; p=p+2*dy;

x=x+1; y=y+1;

p=p+(2*dy)-(2*dx);

}

putpixel(x,y,7);

}

getch(); closegraph();

}

### Output: ### Questions Bank

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