#include<stdio.h>
#include<graphics.h>
#include<math.h>
#include<conio.h>
#define x0 400    //定義全局變量x0,y0:坐標軸中心（x0,y0)
#define y0 300           
void Bresenham(int x1, int y1, int x2, int y2) 
{
 int x, y, dx, dy, p1, i;
 dx = x2 - x1;            
 dy = y2 - y1;
 if (abs(dx) > abs(dy)) //斜率絕對值在（0,1），步進方向為x軸
 {       
 if (x1 < x2)   //默認畫點從左往右畫
 {         
  x = x1;
  y = y1;
 }
 else
 {
  x = x2;
  y = y2;
 }    
 putpixel(x + x0, y0 - y, RED);
 Sleep(50);
 p1 = 2 * abs(dy) - abs(dx);     //計算初始pi的值
 for (i = min(x1, x2); i < max(x1, x2); i++) 
 {
  x = x + 1;
  if (p1 >= 0) 
  {
  if (dx*dy >= 0)
   y = y + 1;
  else
   y = y - 1;  //若Pi>=0,y(i+1)=y(i)±1
  p1 = p1 + 2 * (abs(dy) - abs(dx));  //更新pi
  }
  else 
  {
  y = y;     //若Pi<0,y(i+1)=y(i)
  p1 = p1 + 2 * abs(dy);   //更新pi
  }
  putpixel(x + x0, y0 - y, RED);
  Sleep(50);
 }
 }
 else 
 {
 if (y1 < y2) 
 {       //步進方向為y軸，默認畫點從下往上畫     
  x = x1;
  y = y1;
 }
 else 
 {
  x = x2;
  y = y2;
 }
 putpixel(x + x0, y0 - y, RED);
 Sleep(50);
 p1 = 2 * abs(dx) - abs(dy);
 for (i = min(y1, y2); i < max(y1, y2); i++) 
 {
  y = y + 1;
  if (p1 >= 0) 
  {
  if (dx*dy >= 0)   //判斷x方向是增加還是減少，很關鍵
   x = x + 1;
  else
   x = x - 1;
  p1 = p1 + 2 * (abs(dx) - abs(dy));
  }
  else 
  {
  x = x;
  p1 = p1 + 2 * abs(dx);
  }
  putpixel(x + x0, y0 - y, RED);
  Sleep(50);
 }
 }
}
void main() 
{
 int x1, x2, y1, y2;
 printf("請輸入兩個整數(shù)點的坐標(x1,y1),(x2,y2)\n");
 scanf("%d %d %d %d", &x1, &y1, &x2, &y2);
 initgraph(800, 600);  //初始化圖形窗口大小
 setbkcolor(WHITE);
 cleardevice();
 setcolor(BLACK);
 line(0, y0, x0 * 2, y0); //坐標軸X
 line(x0, 0, x0, y0 * 2); //坐標軸Y
 Bresenham(x1, y1, x2, y2);      //Bresenham畫線算法
 _getch();     //等待一個任意輸入結束
 closegraph();     //關閉圖形窗口
}