Anchor

▶ View interactive demo

Open in turtleSpaces IDERun starscape to create a galaxy of randomly-shaped and colored stars.

TO star :radius :points :size :filled
  ;takes number number number boolean (true or false)
  ;eg star 10 9 40 false
  ;or star 20 5 50 true

  pu dropanchor tether
  ;pull up the turtle pen, drop the 'anchor' to set the 'anchor point' to the current position, and do not change it if the turtle's rotation changes (tether)
  ;the anchor point is the point the orbit primitives orbit around

  if :filled [polyspot :radius :points * 2
    if oddp :points [rt 360 / :points / 4]]
  ;if creating a filled star, create a polygon to fill in the center
  ;if the star has an odd number of points, we need to turn a little

  pullout :radius
  ;pull out from the anchor point, which is currently the turtle's position

  repeat :points [
    ;repeat once for each point:

    pu make "position position
    ;set the :position container to the current turtle position

    orbitleft 360 / :points / 2
    ;orbit around the anchor point (in this case the center) to the left
    ;a fraction of 360 degrees divided by the number of points divided by 2

    pullout :size
    ;pull the turtle out from the center of the star (anchor point)

    setvectors direction :position
    ;point the turtle toward the previous position

    if not :filled [pd line distance position :position]
    ;if not making a filled star, create a line in front of the turtle of
    ;the length required for its end to be the previous turtle position.

    if :filled [frag]
    ;if creating a filled star, create a 'fragment' based on the last three
    ;turtle positions

    pu make "position position
    ;set the :position container to the current position

    pullin :size
    ;pull the turtle in toward the center of the star (anchor point)

    orbitleft 360 / :points / 2
    ;orbit to the left again a similar amound to the last orbitleft

    setvectors direction :position
    ;point toward the previous position

    if not :filled [pd line distance position :position]
    ;create a line if not a filled star similarly to the previous line

    if :filled [frag]
    ;create a fragment if a filled star similarly to the previous frag

  ]
END

TO starscape
  reset ht snappy:setposition [0 0 0] snappy:dropanchor repeat 200 [pu home randvec fd 1000 + random 1000 up 90 snappy:setvectors direction myrtle:position randfc randpc randps randfs star 10 + random 100 3 + random 20 10 + random 90 randbool]
END