lovr-template/xform.lua

Xform = {}
Xform.__index = Xform

-- TODO
-- [x] optional constructor args, usually want to set pos, maybe rot
-- [x] values should be copied into persistant properties
-- [ ] ensure that `xform.position.x += 1` triggers an update
-- [x] allow user data
-- [x] fns to add and remove children from parent
-- [ ] prevent DAG cycle in parent/child
-- [ ] correct mat4 calc (need to do parent.world * child.local??)
-- [ ] ensure children vector is loop/remove safe
-- [ ] parenting xform should preserve it's world space in the new 
--     parent local
-- [ ] stub out all transform fns from Unity
-- [ ] write test suite?

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
end

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

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

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

local function mount(child, parent)
  assert(parent == nil or is_xform(parent), "parent must be an Xform")
  assert(child ~= parent, "parent can't be self")
  if child['parent'] == parent then return end

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

function Xform:new(position, scale, rotation)
  local o = {
    __members = {
      type     = "Xform",
      mat4     = lovr.math.newMat4(),
      parent   = nil,
      children = {},
      -- TODO these need to be copied over
      position = position or lovr.math.newVec3(),
      scale    = scale or lovr.math.newVec3(1),
      rotation = rotation 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)
    return self.__members[index]
end

return Xform