Box2D - filterData helper

eezing

Here's a simple little function to manage filterData for Box2d.

local categories = { __categoryIndex = 1 }   local function getCategory(...)   local value = 0   for i, name in ipairs(arg) do   if not categories[name] then   local v = categories.__categoryIndex * 2 categories.__categoryIndex = v categories[name] = v value = value + v   else   value = value + categories[name]   end end   return value end     -- Use --   local categoryBits = getCategory("car") -- New category local maskBits = getCategory("car") -- Will only collide with cars print(categoryBits, maskBits) --> 2, 2   local categoryBits = getCategory("plane") -- New category local maskBits = getCategory("plane") -- Will only collide with planes print(categoryBits, maskBits) --> 4, 4   local categoryBits = getCategory("plane") -- Use existing category local maskBits = getCategory("plane", "car") -- Collide with both cars and planes print(categoryBits, maskBits) --> 4, 6   local categoryBits = getCategory("car") -- Use existing category local maskBits = getCategory("plane", "car", "boat") -- Collide with cars, planes, and boats (will create new 'boat' category) print(categoryBits, maskBits) --> 2, 14