theory

src/generators/MapDisplay.moon

@@ -0,0 +1,34 @@
+import graphics from love
+import cos, sin from math
+
+w, h = graphics.getDimensions!
+
+tiny = require "tiny"
+IDTracker = require "systems/IDTracker"
+
+MapDisplay = (system_id) ->
+  return tiny.sortedSystem {
+    compare: (a, b) =>
+      if a.orbit and b.orbit
+        a.orbit.hierarchy <= b.orbit.hierarchy
+      else
+        true
+    filter: tiny.requireAny "orbit", tiny.requireAll("x", "y", system_id)
+    draw: (t) =>
+      graphics.translate w / 2, h / 2
+      for entity in *@entities
+        if orbit = entity.orbit
+          orbit = entity.orbit
+          -- orbital period
+          --  real: T = 2pi * sqrt(a^3 / G*M)
+          --  sim:  T = 2pi * speed_parameter
+          entity.x = orbit.radius * cos(t / orbit.speed_parameter) + orbit.offset
+          entity.y = orbit.radius * sin(t / orbit.speed_parameter) + orbit.offset
+          if orbit.parent_id
+            parent = IDTracker[orbit.parent_id]
+            entity.x += parent.x
+            entity.y += parent.y
+        graphics.circle "fill", entity.x, entity.y, 5 -- TEMP radius
+  }
+
+return MapDisplay

src/main.moon

@@ -1,4 +1,5 @@
 tiny = require "tiny"
+MapDisplay = require "generators/MapDisplay"
 
 systems = {}
 for name in *love.filesystem.getDirectoryItems "systems"
@@ -17,11 +18,14 @@ makeEntity = (tab) ->
   return tab
 
 world = tiny.world game, unpack systems
+local map
 
 system = ->
+  system_id = "someuuidthing"
   sun = makeEntity {
     x: 0,
     y: 0
+    [system_id]: true
   }
   planet = makeEntity {
     orbit: {
@@ -31,8 +35,11 @@ system = ->
       offset: love.math.random!
       speed_parameter: 0.5
     }
+    [system_id]: true
   }
+  map = MapDisplay system_id
   world\add sun, planet
+  world\add map
 
 system!
 
@@ -40,7 +47,7 @@ love.update = (dt) ->
   world\update dt
 
 love.draw = ->
-  systems.MapDisplay\draw game.time
+  map\draw game.time
 
 love.keypressed = (key) ->
   if key == "escape" love.event.quit!

src/systems/disabled/MapDisplayManager.moon

@@ -0,0 +1,59 @@
+import graphics from love
+import cos, sin from math
+
+w, h = graphics.getDimensions!
+
+tiny = require "tiny"
+IDTracker = require "systems/IDTracker"
+
+
+
+MapDisplayManager = tiny.system {
+  known: {}
+  filter: tiny.requireAll "system_id"
+  onAdd: (entity) =>
+    unless @known[entity.system_id]
+      @known[entity.system_id] = true
+      makeDisplay entity.system_id
+  onRemove: (entity) =>
+}
+
+
+
+IDTracker = tiny.system {
+  filter: tiny.requireAll "id"
+  onAdd: (entity) =>
+    @[entity.id] = entity
+  onRemove: (entity) =>
+    @[entity.id] = nil
+}
+return MapDisplayManager
+
+
+
+
+MapDisplay = tiny.sortedSystem {
+  compare: (a, b) =>
+    if a.orbit and b.orbit
+      a.orbit.hierarchy <= b.orbit.hierarchy
+    else
+      true
+  filter: tiny.requireAny "orbit", tiny.requireAll("x", "y")
+  draw: (t) =>
+    graphics.translate w / 2, h / 2
+    for entity in *@entities
+      if orbit = entity.orbit
+        orbit = entity.orbit
+        -- orbital period
+        --  real: T = 2pi * sqrt(a^3 / G*M)
+        --  sim:  T = 2pi * speed_parameter
+        entity.x = orbit.radius * cos(t / orbit.speed_parameter) + orbit.offset
+        entity.y = orbit.radius * sin(t / orbit.speed_parameter) + orbit.offset
+        if orbit.parent_id
+          parent = IDTracker[orbit.parent_id]
+          entity.x += parent.x
+          entity.y += parent.y
+      graphics.circle "fill", entity.x, entity.y, 5 -- TEMP radius
+}
+
+return MapDisplay