collisions.lua

collisions.lua

-- local functions like this one are only visible (you can only acces them) from the module (file). This is
-- a good practice to not pollute global namespace with things that are not supposed to be there.
-- This function just check if 2 rectangles collides and returns true or false.
local function checkCollision(a, b)
  return a.x < b.x + b.w and
         a.x + a.w > b.x and
         a.y < b.y + b.h and
         a.h + a.y > b.y
end

-- "move" tries to move "item" to position (new_x, new_y)
function mt:move(item, new_x, new_y)
  -- First we store current position, we'll roll back if we encounter any obstacle.
  local prev_x, prev_y = item.x, item.y

  -- Let's be optimistic and assign the new values.
  item.x, item.y = new_x, new_y

  for _, other in ipairs(self.items) do
    -- if any other item collides with moved one ("item") then let's just roll back to the position it was
    -- before the function was called
    if other ~= item and checkCollision(item, other) then
      item.x, item.y = prev_x, prev_y
      break -- "break" exits the loop imidiately
    end
  end
end