dim 150 150

% calculates direction based on rotation 0 - right ,1 - up ,2 - left , 3- down
% rotation can be +1 - clockwise and -1 counterclockwise
procedure calculateDir { dir rot newDir }
{
       expression newDir { dir + rot }
       if_then_else { newDir == -1 }
       {
             number newDir 3
        }
       {
        }
       if_then_else { newDir == 4 }
       {
             number newDir 0
        }
       {
        }
}

% draws a line based on the start Point and direction and returns end point
procedure step { dir stepLength startPoint returnPoint }
{
     getx startPointX startPoint
     gety startPointY startPoint
     if_then_else { dir == 0 }
     {
              expression newX { startPointX + stepLength }
              point returnPoint newX startPointY
     }
    {
     }
     if_then_else { dir == 1 }
     {
              expression newY { startPointY + stepLength }
              point returnPoint startPointX newY
     }
    {
     }
     if_then_else { dir == 2 }
     {
              expression newX { startPointX - stepLength }
              point returnPoint newX startPointY
     }
    {
     }
     if_then_else { dir == 3 }
     {
              expression newY { startPointY -  stepLength }
              point returnPoint startPointX newY
     }
    {
     }
     drawsegment startPoint returnPoint
}

% draws Hilbert curve with given direction order and start point
procedure hilbert { dir rot order stepLength startPoint returnPoint }
{
     expression negRot { ( -1 ) * rot }
     expression newOrder { order - 1 }

     if_then_else { order > 0 }
     {
           call calculateDir { dir rot dir2 }

           call hilbert { dir2 negRot newOrder stepLength startPoint returnPoint1 }           
           call step { dir2 stepLength returnPoint1 returnPoint2 }       

           call calculateDir { dir2 negRot dir3 }

           call hilbert { dir3 rot newOrder stepLength returnPoint2 returnPoint3  }
           call step { dir3 stepLength returnPoint3 returnPoint4 }

          call hilbert { dir3 rot newOrder stepLength returnPoint4 returnPoint5 }
          call calculateDir { dir3 negRot dir4 }
          call step { dir4 stepLength returnPoint5 returnPoint6 }

          call hilbert  {dir4 negRot newOrder stepLength returnPoint6 returnPoint7 }

         getx returnPointX returnPoint7
         gety returnPointY returnPoint7
         point returnPoint returnPointX returnPointY
           
    }
    {
         getx returnPointX startPoint
         gety returnPointY startPoint

         point returnPoint returnPointX returnPointY 
    }
} 


point numOfIterations 1 0 7 0
animation_frames 7 1

getx n numOfIterations
expression stepLength { 150 / pow( 2 , n )}
expression startX { 75 / pow(2,n) }
expression startY { 75 / pow(2,n) }

point start startX startY
call hilbert { 0 1 n stepLength  start return }