<file tcl> # ORBITALKIT - CC0 2023 Arcade Wise # Create a planet using “Claim $this is Earth” # Create a satellite using “Claim $this is a satellite”

proc orbitalVelocityAroundEarth {radius} {

  set EarthMass [expr {5.972168 * (10 ** 18)}]
  set G [expr {6.67430 * (10.0 ** (-11.0))}]

  return [expr {sqrt(($G * $EarthMass) / $radius)}]

}

When /someone/ claims /earth_page/ is Earth {

  When $earth_page has region /earth/ {
      # Draw a little earth :>
      lassign [region centroid $earth] x_earth y_earth
      Display::circle $x_earth $y_earth 100 5 green

      Wish $earth_page is labelled Earth

      When /someone/ claims /sat_page/ is a satellite  { 
          When $sat_page has region /sat/ & the clock time is /t/ & /sat/ has tag /tag/ {
              set radius [vec2 distance [region centroid $earth] [region centroid $sat]]
              
              # Display the orbit circle
              Display::circle $x_earth $y_earth $radius 5 darkblue

              set speed [orbitalVelocityAroundEarth [expr {$radius * 1000}]]
          
              # Calculate postion for sattelite
              set angle [expr {(round(($t * 200 + ($tag * 100))) % 2000) / 2000.0}]
              set x [expr {($radius * sin(6.283 * $angle )) + $x_earth}]
              set y [expr {($radius * cos(6.283 * $angle )) + $y_earth}]

              # display the stroke 
              Display::stroke [list [region centroid $earth] [list $x $y]] 1 red

              Display::circle $x $y 20 5 white true
              Display::text $x [expr {$y - 40 }] 1 "[expr {round($speed)}]km/s at [expr {int($radius) * 1000}]km from Earth" [region angle $earth]
          }
      }
  }

}

</code>