Bresenham's Line Algorithm (THICK LINE)

The Bresenham algorithm is an incremental scan conversion algorithm.

The big advantage of this algorithm is that, it uses only integer calculations. Moving across the x axis in unit intervals and at each step choose between two different y coordinates.

For example, from below figure, from position (2, 3) you need to choose between (3, 3) and (3, 4). You would like the point that is closer to the original line.

Image source: Tutorialspoint

We can draw various types of lines using Bresenham's Line Algorithm such as:
  1. SOLID LINE
  2. DOTTED LINE
  3. DASHED LINE
  4. THICK LINE

Below is a code to draw a Thick Line using Bresenham's Line Algorithm.

Code:

	/*
	Title: Bresenham's Line Algorithm (THICK LINE)
	Description: An algorithm to draw a Thick Line using Bresenham's Line Drawing Algorithm
	Author: Saideep Dicholkar
	*/
	#include<stdio.h>
	#include<graphics.h>
	#include<math.h>
	void bline(float x1,float y1,float x2,float y2);
	void main()
	{
	int gd=DETECT,gm;
	float wy,wx,x1,y1,x2,y2;
	int i,thickness;
	initgraph(&gd,&gm,"");
	printf("Enter x1,y1,x2,y2:\n");
	scanf("%f%f%f%f",&x1,&y1,&x2,&y2);
	printf("\nEnter thickness of line: ");
	scanf("%d",&thickness);
	bline(x1,y1,x2,y2);
	if((y2-y1)/(x2-x1)<1)
	{
	wy=(thickness-1)*sqrt(pow((x2-x1),2)+pow((y2-y1),2))/(2*fabs(x2-x1));
	for(i=0;i<wy;i++)
	{
	bline(x1,y1-i,x2,y2-i);
	bline(x1,y1+i,x2,y2+i);
	}
	}
	else
	{
	wx=(thickness-1)*sqrt(pow((x2-x1),2)+pow((y2-y1),2))/(2*fabs(y2-y1));
	for(i=0;i<wx;i++)
	{
	bline(x1-i,y1,x2-i,y2);
	bline(x1+i,y1,x2+i,y2);
	}
	}
	getch();
	closegraph();
	restorecrtmode();
	}
	void bline(float x1,float y1,float x2,float y2)
	{
	float xinc,yinc,x,y;
	float dx,dy,e;
	dx=abs(x2-x1);
	dy=abs(y2-y1);
	if(x1<x2)
	xinc=1;
	else
	xinc=-1;
	if(y1<y2)
	yinc=1;
	else
	yinc=-1;
	x=x1;
	y=y1;
	putpixel(x,y,WHITE);
	if(dx>=dy)
	{
	e=(2*dy)-dx;
	while(x!=x2)
	{
	if(e<0)
	{
	e+=(2*dy);
	}
	else
	{
	e+=(2*(dy-dx));
	y+=yinc;
	}
	x+=xinc;
	putpixel(x,y,WHITE);
	}
	}
	else
	{
	e=(2*dx)-dy;
	while(y!=y2)
	{
	if(e<0)
	{
	e+=(2*dx);
	}
	else
	{
	e+=(2*(dx-dy));
	x+=xinc;
	}
	y+=yinc;
	putpixel(x,y,WHITE);
	}
	}
	}

view raw bthick.c hosted with ❤ by GitHub

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Output:

Thick Line

Note: Just copy the files "CGA.bgi" & "EGAVGA.bgi" from bgi folder to bin. So, if you have copied these 2 files then you can skip writing "C:\\tc\\bgi" in initgraph with just ""(2 double quotes).