Dưới đây là thuật toán Bresenham đầy đủ các trường hợp để vẽ đường thẳng và đường tròn:

Thuật toán Bresenham vẽ đường thẳng:

#include <iostream>
#include <graphics.h>
#define DELAY 10
using namespace std;

void doiCho(int &a, int &b)
{
    int tg=a;
    a=b;
    b=tg;
}

void input(int &x, int &y, char k)
{
    cout<<"Nhap toa do diem "<<k<<endl;
    cout<<"x=";cin>>x;
    cout<<"y=";cin>>y;
}

void drawBresenham(int x1, int y1, int x2, int y2, int c)
{
    int x,y,Const1,Const2,p;
    int dx=x2-x1;
    int dy=y2-y1;
    float m=(float)dy/dx;

    if(x1==x2){
        if(y1>y2) doiCho(y1,y2);
        y=y1;
        while(y<=y2)
        {
            putpixel(x1,y,c);
            y++;
            Sleep(DELAY);
        }
    }else if(y1==y2){
        if(x1>x2) doiCho(x1,x2);
        x=x1;
        while(x<=x2)
        {
            putpixel(x,y1,c);
            x++;
            Sleep(DELAY);
        }
    }else if(m>0&&m<=1){
        if(x1>x2){
                doiCho(x1,x2);
                doiCho(y1,y2);
        }
        dx=x2-x1;dy=y2-y1;
        Const1=2*dy;
        Const2=2*(dy-dx);
        p=2*dy-dx;
        x=x1;y=y1;
        while(x<x2)
        {
            putpixel(x,y,c);
            x++;
            if(p<0) p+=Const1;
            else{
                p+=Const2;
                y++;
            }
            Sleep(DELAY);
        }
    }else if(m>1){
        if(x1>x2){
                doiCho(x1,x2);
                doiCho(y1,y2);
        }
        dx=x2-x1;dy=y2-y1;
        Const1=2*dx;
        Const2=2*(dx-dy);
        p=2*dx-dy;
        x=x1;y=y1;
        while(y<y2)
        {
            putpixel(x,y,c);
            y++;
            if(p<0) p+=Const1;
            else{
                p+=Const2;
                x++;
            }
            Sleep(DELAY);
        }
    }else if(m<0&&m>=-1){
        if(x1>x2){
                doiCho(x1,x2);
                doiCho(y1,y2);
        }
        dx=x2-x1;dy=y2-y1;
        Const1=2*dy;
        Const2=2*(dy+dx);
        p=2*dy+dx;
        x=x1;y=y1;
        while(x<x2)
        {
            putpixel(x,y,c);
            x++;
            if(p>0) p+=Const1;
            else{
                p+=Const2;
                y--;
            }
            Sleep(DELAY);
        }
    }else if(m<-1){
        if(y1>y2){
                doiCho(x1,x2);
                doiCho(y1,y2);
        }
        dx=x2-x1;dy=y2-y1;
        Const1=2*dx;
        Const2=2*(dy+dx);
        p=2*dx+dy;
        x=x1;y=y1;
        while(y<y2)
        {
            putpixel(x,y,c);
            y++;
            if(p>0) p+=Const1;
            else{
                p+=Const2;
                x--;
            }
            Sleep(DELAY);
        }
    }
}

int main()
{
    int x1,y1,x2,y2,c=5;
    input(x1,y1,'A');
    input(x2,y2,'B');
    initwindow(500,600);
    drawBresenham(x1,y1,x2,y2,c);
    line(x1,y1,x2,y2);
    getch();
    return 0;
}

Thuật toán Bresenham vẽ đường tròn:

#include <iostream>
#include <graphics.h>
#define DELAY 10
using namespace std;

void input(int &x, int &y, int &R)
{
    cout<<"Nhap toa do tam va ban kinh:"<<endl;
    cout<<"x=";cin>>x;
    cout<<"y=";cin>>y;
    cout<<"R=";cin>>R;
}

void put8pixel(int x, int y, int x0, int y0, int c)
{
    putpixel(x+x0,y+y0,c);
    putpixel(x+x0,-y+y0,c);
    putpixel(-x+x0,y+y0,c);
    putpixel(-x+x0,-y+y0,c);
    putpixel(y+x0,x+y0,c);
    putpixel(-y+x0,x+y0,c);
    putpixel(y+x0,-x+y0,c);
    putpixel(-y+x0,-x+y0,c);
}

void drawBresenham(int x0, int y0, int R, int c)
{
    int x=0,y=R,p=3-2*R;
    while(x<=y)
    {
        put8pixel(x,y,x0,y0,c);
        if(p<0) p+=4*x-6;
        else{
            p=p-4*y+4*x+10; //icon App on Samsung phone: p-=4*y+4*x+10;
            y--;
        }
        x++;
        Sleep(DELAY);
    }
}

int main()
{
    int x,y,R,c=5;
    input(x,y,R);
    initwindow(500,600);
    drawBresenham(x,y,R,c);
    getch();
    return 0;
}

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