init

src/main.moon

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+math.randomseed os.time!
+w, h = love.graphics.getDimensions!
+body_count = 1000
+starting_area = 1000^2
+percent_scale = 100 / body_count
+radius_scale = 1/4
+G = 100 -- 6.67408e-11
+-- snapshot doubling ??
+time, frame_time, sim_rate = 0, 1/60, 1/60
+
+distance = (A, B) ->
+  local dx, dy
+  dx = A.x - B.x
+  dy = A.y - B.y
+  return math.sqrt dx * dx + dy * dy
+
+gravity = (A, B) ->
+  local dx, dy, d2, F, theta, cos, sin
+  dx = A.x - B.x
+  dy = A.y - B.y
+  d2 = dx * dx + dy * dy
+  -- return if d2 == 0
+  if d2 <= (A.radius + B.radius)^2
+    return
+  F = G * A.mass * B.mass / d2
+  theta = math.atan2 dy, dx
+  cos = math.cos theta
+  sin = math.sin theta
+  A.vx -= (F / A.mass) * cos * sim_rate
+  A.vy -= (F / A.mass) * sin * sim_rate
+  B.vx += (F / B.mass) * cos * sim_rate
+  B.vy += (F / B.mass) * sin * sim_rate
+
+class Body
+  new: =>
+    local d, theta
+    d = math.sqrt(starting_area) / 2
+    theta = math.random! * math.pi * 2
+    @x = math.random! * d * math.cos theta
+    @y = math.random! * d * math.sin theta
+    @vx = math.random! / d
+    @vy = math.random! / d
+    @mass = 1
+    @radius = @mass ^ radius_scale
+
+bodies = {}
+for i = 1, body_count
+  table.insert bodies, Body!
+
+simulate = (bodies) ->
+  for i = 1, #bodies - 1, 2
+    for j = i + 1, #bodies
+      gravity(bodies[i], bodies[j])
+
+  for body in *bodies
+    body.x += body.vx * sim_rate
+    body.y += body.vy * sim_rate
+
+  invalid_bodies = {}
+  for i = #bodies, 2, -2
+    for j = i - 1, 1, -1
+      valid = true
+      for id in *invalid_bodies
+        if i == id or j == id
+          valid = false
+      if not valid
+        continue
+      A = bodies[i]
+      B = bodies[j]
+      -- print i, j
+      -- if not A
+      --   print i, j, #bodies
+      if distance(A, B) <= A.radius + B.radius
+        -- print "#{i} and #{j} collided!", distance(A, B), A.radius + B.radius
+        mass = A.mass + B.mass
+        radius = mass ^ radius_scale
+        -- print mass, radius
+        mx = (A.x * A.mass + B.x * B.mass) / mass
+        my = (A.y * A.mass + B.y * B.mass) / mass
+        vx = (A.vx * A.mass + B.vx * B.mass) / mass
+        vy = (A.vy * A.mass + B.vy * B.mass) / mass
+        A.mass = mass
+        A.radius = radius
+        A.x = mx
+        A.y = my
+        A.vx = vx
+        A.vy = vy
+        table.insert(invalid_bodies, j)
+        -- table.remove(bodies, j)
+        -- j += 1
+
+  table.sort invalid_bodies, (a, b) -> a > b
+  for id in *invalid_bodies
+    -- print id
+    table.remove bodies, id
+  -- print "end"
+
+love.update = (dt) ->
+  simulate bodies
+
+love.draw = ->
+  if #bodies > 1000
+    return
+  love.graphics.setColor 1, 1, 1, 0.25
+  love.graphics.line 0, h / 2, w, h / 2
+  love.graphics.line w / 2, 0, w / 2, h
+  love.graphics.setColor 1, 1, 1, 1
+
+  love.graphics.translate w / 2, h / 2
+  m, x, y = 0, 0, 0
+  for body in *bodies
+    if body.mass > m
+      m = body.mass
+      x = body.x
+      y = body.y
+  love.graphics.translate -x, -y
+  for body in *bodies
+    -- love.graphics.points body.x, body.y
+    love.graphics.circle "fill", body.x, body.y, body.radius
+
+love.keypressed = (key) ->
+  if key == "escape"
+    love.event.quit!