xform/xform.lua

Xform = {}
Xform.__index = Xform

local function index_of(list, o)
  for i,v in pairs(list) do
    if v == o then
      return i
    end
  end
end

function remove(list, o)
  table.remove(list, index_of(list, o))
  return list
end

local function append(list, o)
  list[#list + 1] = o
end

local function copy_v3(s, t)
  t.x = s.x
  t.y = s.y
  t.z = s.z
  return t
end

local function copy_quat(s, t)
  t.x = s.x
  t.y = s.y
  t.z = s.z
  t.w = s.w
  return t
end

local function is_xform(o)
  return o['__members'] and o.__members.type == "Xform"
end

local function update(xform)
  xform.mat4:set(xform.position, xform.scale, xform.rotation)
  if xform.parent then
    xform.mat4:set(xform.parent.mat4 * xform.mat4)
  end
  for i, child in ipairs(xform.__members.children) do
    update(child)
  end
end

local function mount(child, parent)
  assert(parent == nil or is_xform(parent), "parent must be an Xform")
  local _parent = parent
  while _parent do
    assert(_parent ~= child, "cyclical scene graph")
    _parent = _parent.parent
  end
  
  if child['parent'] == parent then return end

  if child['parent'] and child.parent ~= parent then
    remove(child.parent.__members.children, child)
  end
  child.__members.parent = parent
  if parent then
    append(parent.__members.children, child)
  end
  update(child)
end

function Xform:new(position, scale, rotation)
  local o = {
    __members = {
      type     = "Xform",
      mat4     = lovr.math.newMat4(),
      parent   = nil,
      children = {},
      position = position and copy_v3(position, lovr.math.newVec3()) 
                 or lovr.math.newVec3(),
      scale    = scale and copy_v3(scale, lovr.math.newVec3(1)) 
                 or lovr.math.newVec3(1),
      rotation = rotation and copy_quat(rotation, lovr.math.newQuat()) 
                 or lovr.math.newQuat()
    }
  }
  setmetatable(o, Xform)
  update(o)
  return o
end

function Xform:__newindex(index, value)
    if index == "position" or index == "scale" then
      copy_v3(value, self.__members[index])
      update(self)
    elseif index == "rotation" then
      copy_quat(value, self.__members[index])
      update(self)
    elseif index == "parent" then
      mount(self, value)
    elseif index == "children" or
           index == "mat4" then
    elseif index ~= "__members" then
      rawset(self, index, value)
    end
end

function Xform:__index(index)
  if index == "children" then
    return {unpack(self.__members.children)}
  else
    return self.__members[index]
  end
end

return Xform