rotate_box_by_facedir.lua

-- Axis lookup table based on how Minetest's `facedir` operates.
local AXIS_LOOKUP = {
    vector.new( 0,  1,  0), -- +Y
    vector.new( 0,  0,  1), -- +Z
    vector.new( 0,  0, -1), -- -Z
    vector.new( 1,  0,  0), -- +X
    vector.new(-1,  0,  0), -- -X
    vector.new( 0, -1,  0), -- -Y
}

-- Lookup table to find out how to rotate for each `facedir` axis.
local AXIS_ROTATION = {
    nil,
    { vector.new(1, 0, 0),  90 },
    { vector.new(1, 0, 0), -90 },
    { vector.new(0, 0, 1), -90 },
    { vector.new(0, 0, 1),  90 },
    { vector.new(0, 0, 1), 180 },
}

local function rotate_box_by_facedir(box, facedir)
    if facedir == 0 then return end

    local axis_index = math.floor(facedir / 4)
    if axis_index ~= 0 then
        local axis, degrees = unpack(AXIS_ROTATION[1 + axis_index])
        box.min = box.min:rotate_around_axis(axis, math.rad(degrees))
        box.max = box.max:rotate_around_axis(axis, math.rad(degrees))
    end

    local axis_rot = facedir % 4
    if axis_rot ~= 0 then
        local axis = AXIS_LOOKUP[1 + axis_index]
        local degrees = axis_rot * 90
        box.min = box.min:rotate_around_axis(axis, math.rad(degrees))
        box.max = box.max:rotate_around_axis(axis, math.rad(degrees))
    end

    -- Recalculate the proper minimum and maximum bounds, since we just rotated these vectors.
    box.min.x, box.max.x = math.min(box.min.x, box.max.x), math.max(box.min.x, box.max.x)
    box.min.y, box.max.y = math.min(box.min.y, box.max.y), math.max(box.min.y, box.max.y)
    box.min.z, box.max.z = math.min(box.min.z, box.max.z), math.max(box.min.z, box.max.z)
end