box collision algorithm in lua

BoundingBox.lua

-- This script was written by Luiji Maryo, http://github.com/Luiji .
-- It has been released under the Public Domain.

-- Collision detection function.
-- Checks if box1 and box2 overlap.
-- w and h mean width and height.
function CheckCollision(box1x, box1y, box1w, box1h, box2x, box2y, box2w, box2h)
    if box1x > box2x + box2w - 1 or -- Is box1 on the right side of box2?
       box1y > box2y + box2h - 1 or -- Is box1 under box2?
       box2x > box1x + box1w - 1 or -- Is box2 on the right side of box1?
       box2y > box1y + box1h - 1    -- Is b2 under b1?
    then
        return false                -- No collision.  Yay!
    else
        return true                 -- Yes collision.  Ouch!
    end
end