from_entities_and_Model.lua

--[[ Summary: Below, "entity" and "item" may be different types.
              They simply implement same-name methods.
--]]

-- A bit from entities.lua:

function entities.runloop(dt)
  for _, entity in pairs(all_entities) do
    entity:update_and_draw(dt)
  end
end
 
-- A bit from Model.lua (caps because it's a type):

-- Call this as in model:look_at({x, y, z}).                                     
-- This expects the input vector to be approximately a unit vector.               
function Model_mt:look_at(dir)                                                   
  -- Check that the input direction is close to being a unit vector.             
  assert(math.abs(Vec3.length(dir) - 1.0) < 0.001)                                
  for _, item in pairs(self.items) do                                            
    item:look_at(unpack(dir))                                                    
  end                                                                            
end