Speed-optimized Bresenhem algorythm

drawline.c

#include <stdio.h>
#include <stdlib.h>
#include <conio.h>

void plot(int x, int y, int c)
{
	gotoxy(x+1,y+1);
	putchar(c);
	putchar(8);

}

#define DIR_LRTB	0	// LEFT  to RIGHT, TOP    to BOTTOM
#define DIR_RLTB	1	// RIGHT to LEFT,  TOP    to BOTTOM
#define DIR_LRBT	2	// LEFT  to RIGHT, BOTTOM to TOP
#define DIR_RLBT	3	// RIGHT to LEFT,  BOTTOM to TOP

void draw_line(int x0, int y0, int x1, int y1, int c)
{
	int x,y,dx,dy,s;
	char d=0;
	x=x0; y=y0;
	if(x0>x1)d|=1;
	if(y0>y1)d|=2;
	switch(d)
	{
	case DIR_LRTB:
			dx=x1-x0;
			dy=y1-y0;
			if(dy>dx)
			{
				for(s=dx;y<=y1;y++)
				{
					plot(x,y,c);
					s+=dx;
					if(s>=dy){x++;s-=dy;}
				}
			} else
			{
				for(s=dy;x<=x1;x++)
				{
					plot(x,y,c);
					s+=dy;
					if(s>=dx){y++;s-=dx;}
				}
			}
			break;
	case DIR_RLTB:
			dx=x0-x1;
			dy=y1-y0;
			if(dy>dx)
			{
				for(s=dx;y<=y1;y++)
				{
					plot(x,y,c);
					s+=dx;
					if(s>=dy){x--;s-=dy;}
				}
			} else
			{
				for(s=dy;x>=x0;x--)
				{
					plot(x,y,c);
					s+=dy;
					if(s>=dx){y++;s-=dx;}
				}
			}
			break;
	case DIR_LRBT:
			dx=x1-x0;
			dy=y0-y1;
			if(dy>dx)
			{
				for(s=dx;y>=y0;y--)
				{
					plot(x,y,c);
					s+=dx;
					if(s>=dy){x++;s-=dy;}
				}
			} else
			{
				for(s=dy;x<=x1;x++)
				{
					plot(x,y,c);
					s+=dy;
					if(s>=dx){y--;s-=dx;}
				}
			}
			break;
	case DIR_RLBT:
			dx=x0-x1;
			dy=y0-y1;
			if(dy>dx)
			{
				for(s=dx;y>=y0;y--)
				{
					plot(x,y,c);
					s+=dx;
					if(s>=dy){x--;s-=dy;}
				}
			} else
			{
				for(s=dy;x>=x0;x--)
				{
					plot(x,y,c);
					s+=dy;
					if(s>=dx){y--;s-=dx;}
				}
			}
			break;
	}
}

void bresenham_line(int x0, int y0, int x1, int y1, int c)
{
	int x,y,dx,dy,err,derr;
	dx=abs(x1-x0);
	dy=abs(y1-y0);
	err=0;
	derr=dy;
	y=y0;
	for(x=x0;x<=x1;x++)
	{
		plot(x,y,c);
		err+=derr;
		if((2*err)>=dx){y--;err-=dx;}
	}
}

int main(int argc, char **argv)
{
	bresenham_line(5, 17, 39, 3, '#');
	draw_line(     5, 20, 39, 6, '#');
	gotoxy(1,1);
    return 0;
}