Bresenham Line ( relative ) implementation
written/tested in Daz Studio but will be in an arduino Leonardo plotter firmware

var dirx;
var diry;

plot( -10, -3 );

function plot( dx, dy ) // this is a relative movement
{
  dirx = ( dx >= 0 );
  diry = ( dy >= 0 );
  var adx = Math.abs( dx );
  var ady = Math.abs( dy );
  if( adx >= ady ) 
  {
   subplot( 0, adx, ady );
  }
  else
  {
   subplot( 1, ady, adx );
  }
}

function subplot( horizVert, dx, dy )
{  
  var D = 2 * dy - dx;
  var stepy = 0;
  for( x = 1; x <= dx; x++ )
  {
    if( D > 0 )
    {
       stepy = 1;
       D = D - dx;
 }
    D = D + dy;
   if( horizVert == 0 )
   {
     subsubplot( 1, stepy );
 }
 else
 {
     subsubplot( stepy, 1 );
 }    
 stepy = 0;
  }
}

function subsubplot( stepx, stepy )
{
 debug( stepx, stepy );
}