scr_obj_line

///scr_obj_line(x1,y1,x2,y2,object,snapx,snapy)
//              0  1  2  3  4      5     6
//specify object as undefined if you want a list returned.
//otherwise it creates objects specified in argument4.
//list contains arrays (xy[0] -> x, xy[1] -> y)
var dx,dy,d,slopegt1,iny,ie,ine,tmp,sx,sy;
var dsxy, returnlist;
returnlist=argument4!=undefined;
if (returnlist) then dsxy=ds_list_create();
x1=round(argument0/argument5)*argument5;
y1=round(argument1/argument6)*argument6;
x2=round(argument2/argument5)*argument5;
y2=round(argument3/argument6)*argument6;
sx=argument5;
sy=argument6;
slopegt1=0;
dx=abs(x2-x1);
dy=abs(y2-y1);
//NE to NW and SW to SE (dy>dx)
//but take into account new slope
//for when snaps are different
var tpdir=point_direction(x1,y1,x2,y2)
if (tpdir>=45 and tpdir=dx/sx){
  //mirror diagonally
  tmp=x1;//swap x1 with y1
  x1=y1;
  y1=tmp;
  tmp=x2;//swap x2 with y2
  x2=y2;
  y2=tmp;
  tmp=dx;//swap dx with dy
  dx=dy;
  dy=tmp;
  slopegt1=1;
  sx=argument6;
  sy=argument5;
}
if (x1>x2){
  //mirror horizontally/vertically
  tmp=x1;//swap x1 with x2
  x1=x2;
  x2=tmp;
  tmp=y1;//swap y1 with y2
  y1=y2;
  y2=tmp;
}
if (y1>y2){
  iy=-sy;
} else {
  iy=sy;
}
d=(2*dy/sy-dx/sx);
ie=2*dy/sy;
ine=2*(dy/sy-dx/sx);
while(x1<x2){
  if(d<=0){
    d+=ie;
  } else {
    d+=ine;
    y1+=iy;
  }
  x1+=sx;
  if(slopegt1){
    if (returnlist){
      instance_create(y1,x1,argument4);
    } else {
      var xy=0;
      xy[1]=x1;
      xy[0]=y1;
      ds_list_add(dsxy,xy);
    }
  } else {
    if (returnlist){
    instance_create(x1,y1,argument4);
    } else {
      var xy=0;
      xy[1]=y1;
      xy[0]=x1;
      ds_list_add(dsxy,xy);
    }
  }
}
if (returnlist) then return dsxy;