code.cpp

# triangle
to rotate about the origin & a fixed point
#include "stdafx.h"
#include<stdio.h>

#include<math.h>
#include<GL/glut.h>
int xs,ys,xe,ye;
void myInit()
{
	glClearColor(1.0,1.0,1.0,1.0);
	gluOrtho2D(0,500,0,500);
}
void draw_pixel(int x,int y)
{
	glColor3f(1.0,0.0,0.0);
	glPointSize(2.0);
	glBegin(GL_POINTS);
	glVertex2i(x,y);
	glEnd();
}
void bresenhams_line_draw(int x1,int y1,int x2,int y2)
{
	int dx,dy,i,p;
	int incx=1,incy=1;
	int x,y;
	dx=abs(x2-x1);
	dy=abs(y2-y1);
	if(x2<x1)
	{
		incx=-1;
	}
	if(y2<y1)
	{
		incy=-1;
	}
	x=x1;
	y=y1;
	if(dx>dy)
	{
	draw_pixel(x,y);
	p=2*dy-dx;
		for(i=0;i<dx;i++)
		{
			if(p>=0)
			{
				y+=incy;
				p+=2*(dy-dx);
			}
			else
			
				p+=2*dy;
			x+=incx;
			draw_pixel(x,y);
		}
	}
	else{
		draw_pixel(x,y);
	p=2*dx-dy;
		for(i=0;i<dy;i++)
		{
			if(p>=0)
			{
				x+=incx;
				p+=2*(dx-dy);
			}
			else
			
				p+=2*dx;
			y+=incy;
			draw_pixel(x,y);
		}
	}
}

void display()
{
	glClear(GL_COLOR_BUFFER_BIT);
	bresenhams_line_draw(xs,ys,xe,ye);
		glFlush();
}
void main()
{
	printf("enter the start point(x1,y1)\n");
	scanf("%d%d",&xs,&ys);
    printf("enter the end points(x2,y2)\n");
	scanf("%d%d",&xe,&ye);
	glutInitDisplayMode(GLUT_RGB);
	glutInitWindowSize(500,500);
	glutCreateWindow("Bresenhams line drawing");
	myInit();
	glutDisplayFunc(display);
	glutMainLoop();
}