/********Joshua G. Schafrath   Computer Graphics************/
#include <stdio.h>
#include <math.h>
#include "mygraph.h"
#include "point.h"
#include "Xroutines.h"

dc_draw_line ( line aline, environment * env) {
   int dx,dy,y,d,incE,incNE,inc,xsign,ysign;
   point  pt;
   
   printf("line %d %d %d %d\n",aline.e1.x,aline.e1.y,aline.e2.x,aline.e2.y);
   fflush(stdout);
      
   dy = aline.e1.y - aline.e2.y;
      
   /***if the line is vertical, just loop thru the y's for x***/
   if((dx=aline.e1.x-aline.e2.x)==0){
       pt.x= aline.e1.x;
       if(dy >= 0){ /*upward line*/
           for(pt.y=aline.e1.y; pt.y > (aline.e2.y-1); pt.y--){
               printf("%d %d\n",pt.x,pt.y); fflush(stdout);
               dc_draw_point(pt, env);
           }
       }
       else{ /*downward line*/
           for(pt.y=aline.e1.y; pt.y < (1+aline.e2.y); pt.y++){
               printf("%d %d\n",pt.x,pt.y); fflush(stdout);
               dc_draw_point(pt, env);
           }
       }
   }
   
   /***if the line is horizontal, just loop thru the x's for y***/
   else if(dy==0){
       pt.y= aline.e1.y;
       if(dx >= 0){ /*left line*/
           for(pt.x=aline.e1.x; pt.x > (aline.e2.x-1); pt.x--){
               printf("%d %d\n",pt.x,pt.y); fflush(stdout);
               dc_draw_point(pt, env);
           }
       }
       else{ /*right line*/
           for(pt.x=aline.e1.x; pt.x < (1+aline.e2.x); pt.x++){
               printf("%d %d\n",pt.x,pt.y); fflush(stdout);
               dc_draw_point(pt, env);
           }
       }
   }
   
   /***if the line is a diagonal, just loop changing x and y***/
   else if((abs(dy)) == (abs(dx))){
       pt.y= aline.e1.y;
       if(dx >= 0){ /*left line*/
           if(dy >= 0) inc=-1; /*upward line*/
           else inc=1; /*downward line*/
           for(pt.x=aline.e1.x; pt.x > (aline.e2.x-1); pt.x--){               
               printf("%d %d\n",pt.x,pt.y); fflush(stdout);
               dc_draw_point(pt, env);
               pt.y= pt.y + inc;
           }
       }
       else{ /*right line*/
           if(dy >= 0) inc=-1; /*upward line*/
           else inc=1; /*downward line*/    
           for(pt.x=aline.e1.x; pt.x < (1+aline.e2.x); pt.x++){               
               printf("%d %d\n",pt.x,pt.y); fflush(stdout);
               dc_draw_point(pt, env);
               pt.y= pt.y + inc;
           }
       }
   }
   
   
   else{ /* not a vertical, horizontal, or diagonal line */       
       if((abs(dx)) > (abs(dy))){ /*sections 4,5,1,and8*/
           if(dy < 0){              /* down */
               inc=1;xsign=1;ysign=-1;
               if(dx > 0) xsign=-1;  /*left*/
           }     
           else{                    /* up */
               inc=-1;xsign=1;ysign=1;
               if(dx > 0) xsign=-1;   /*left*/
           }           
             
           d = (2 * (ysign * dy)) + (xsign * dx);
           incE = 2 * (ysign * dy);
           incNE = 2 * ((ysign * dy) + (xsign *dx));
           pt.y = aline.e1.y;
              
           if (dx < 0){ /*section 1 and 8*/
               for (pt.x=aline.e1.x; pt.x < (1+aline.e2.x); pt.x++){              
                   printf("%d %d %d\n",pt.x,pt.y,d); fflush(stdout);
                   dc_draw_point(pt, env);
                   if (d > 0){
                       d = d + incNE;
                       pt.y = pt.y + inc;
                   }else{
                       d = d + incE;
                   }
               }
           }
           else{ /*section 4 and 5*/
               for (pt.x=aline.e1.x; pt.x > (aline.e2.x-1); pt.x--){
                   printf("%d %d %d\n",pt.x,pt.y,d); fflush(stdout);
                   dc_draw_point(pt, env);
                   if (d > 0){
                       d = d + incNE;
                       pt.y = pt.y + inc;
                   }else{
                       d = d + incE;
                   }
               }
           }
       }
       else{ /* sections 2,3,6,and7 */
           if(dx < 0){              /* right */
               inc=1;ysign=1;xsign=-1;
               if(dy > 0) ysign=-1;  /*up*/
           }     
           else{                    /* left */
               inc=-1;ysign=1;xsign=1;
               if(dy > 0) ysign=-1;   /*down*/
           }           
             
           d = (2 * (xsign * dx)) + (ysign * dy);
           incE = 2 * (xsign * dx);
           incNE = 2 * ((xsign * dx) + (ysign *dy));
           pt.x = aline.e1.x;
              
           if (dy < 0){ /*section 6 and 7*/
               for (pt.y=aline.e1.y; pt.y < (1+aline.e2.y); pt.y++){              
                   printf("%d %d %d\n",pt.x,pt.y,d); fflush(stdout);
                   dc_draw_point(pt, env);
                   if (d > 0){
                       d = d + incNE;
                       pt.x = pt.x + inc;
                   }else{
                       d = d + incE;
                   }
               }
           }
           else{ /*section 2 and 3*/
               for (pt.y=aline.e1.y; pt.y > (aline.e2.y-1); pt.y--){
                   printf("%d %d %d\n",pt.x,pt.y,d); fflush(stdout);
                   dc_draw_point(pt, env);
                   if (d > 0){
                       d = d + incNE;
                       pt.x = pt.x + inc;
                   }else{
                       d = d + incE;
                   }
               }
           }
       }
       
   }
}