Inventory Placement

local player = game.Players.LocalPlayer
local mouse = player:GetMouse()

local gui = script.Parent
local frameMain = gui:WaitForChild("Frame")

local amount = 12 -- total = amount^2

for y = 1, amount do
    for x = 1, amount do
        local newFrame = Instance.new("Frame")
        newFrame.ZIndex = 2
        newFrame.Size = UDim2.new(0, frameMain.AbsoluteSize.X / amount, 0, frameMain.AbsoluteSize.Y / amount)
        newFrame.Position = UDim2.new(0, (x - 1) * frameMain.AbsoluteSize.X / amount, 0, (y - 1) * frameMain.AbsoluteSize.Y / amount)
        newFrame.Parent = frameMain
    end
end

local dragging = false

local thing = Instance.new("Frame")
thing.ZIndex = 3
thing.Size = UDim2.new(0, frameMain.AbsoluteSize.X / amount, 0, frameMain.AbsoluteSize.Y / amount)
thing.Position = UDim2.new(0.5, -thing.Size.X.Offset / 2, 0, 0)
thing.BackgroundColor3 = Color3.new(0, 1, 0)
thing.InputBegan:Connect(function(input)
    if input.UserInputType ~= Enum.UserInputType.MouseButton1 then
        return
    end

    dragging = true
end)
thing.InputEnded:Connect(function(input)
    if input.UserInputType ~= Enum.UserInputType.MouseButton1 then
        return
    end

    dragging = false

    local frames = frameMain:GetChildren()
    do
        local mousePos = Vector2.new(input.Position.X, input.Position.Y)
        table.sort(frames, function(f1, f2)
            local f1Pos = f1.AbsolutePosition + f1.AbsoluteSize / 2
            local f2Pos = f2.AbsolutePosition + f2.AbsoluteSize / 2

            return (mousePos - f1Pos).Magnitude < (mousePos - f2Pos).Magnitude
        end)
    end

    thing.Position = UDim2.new(0, frames[1].AbsolutePosition.X, 0, frames[1].AbsolutePosition.Y)
end)

game:GetService("RunService").RenderStepped:Connect(function()
    if dragging then
        thing.Position = UDim2.new(0, mouse.X - thing.Size.X.Offset / 2, 0, mouse.Y - thing.Size.Y.Offset / 2)
    end
end)

thing.Parent = gui