*process source xref or(!);
 brbn:Proc Options(main);
 /*********************************************************************
 * 21.05.2014  Walter Pachl
 * Implementing the pseudo code of
 *    http://en.wikipedia.org/wiki/Bresenham%27s_line_algorithm
 * under 'Simplification' (see also REXX version 2)
 *********************************************************************/
grid.=
 dcl image(-2:7,-4:11) char(1);
 image='.';
 image(*,0)='-';
 image(0,*)='|';
 image(0,0)='+';
 call draw_line(-1,-3,6,10);
 Dcl (i,j) Bin Fixed(31);
 Do j=11 To -4 By -1;
   Put Edit(j,' ')(Skip,f(2),a);
   Do i=-2 To 7;
     Put Edit(image(i,j))(a);
     End;
   End;
 Put Edit('   2101234567')(Skip,a);

 draw_line: procedure (x0,y0,x1,y1);
 dcl (x0,y0,x1,y1) fixed binary(31);
 dcl (dx,dy,sx,sy,err,e2) fixed binary(31);

 dx = abs(x1-x0);
 dy = abs(y1-y0);
 if x0 < x1 then sx = 1;
            else sx = -1;
 if y0 < y1 then sy = 1;
            else sy = -1;
 err = dx-dy;

 Do Until(x0=x1&y0=y1);
   image(x0,y0)='X';
   e2=err*2;
   if e2>-dy then do;
     err=err-dy;
     x0=x0+sx;
     End;
   if e2<dx then do;
     err=err+dx;
     y0=y0+sy;
     End;
   End;
 image(x0,y0)='X';
 end;
 end;