How to detect scrolling of mouse wheel

[puf0chek (pushok)]

I’m doing an inventory script roughly speaking. I need some kind of event, which will detect mouse wheel scrolling. It would be desirable that there would be 2 events. Up and down. To do when the scrolled wheel down, things have changed as in Minecraft from left to right, and when the wheel is scrolled up, on the contrary. Searched for the events in UserInputService and couldn’t find it. Help…

[Sepruko (Nat)]

Since I still receive the occasional like on this post even a couple years later, this recent (as of this edit) announcement may change how detecting mouse and trackpad scrolling works.

Upcoming changes to scroll delta behavior

Hi Creators, We’re releasing an overhaul of how the engine handles scroll and trackpad inputs. For the most part this is a strict improvement, enabling the trackpad behavior people expect and fixing some nasty bugs, but it has some small backwards compatibility considerations. In this post we’ll go over the current state of things, the new changes, and what potential problems to double check for in your scripts. TL;DR: The way the engine gets scroll inputs from trackpad / MagicMouse is chang…

The original answer is still below for posterity’s sake. I may update it to reflect the upcoming changes if I find the time if required, but it makes mentions of possible system-specific behavior and I have no MacOS devices to test on.

---

local UserInputService = game:GetService("UserInputService")

-- Method 1, allows for separating pointer logic.
-- We don't need the pan or pinch arguments for mousewheel detection.
UserInputService.PointerAction:Connect(function(wheel, _pan, _pinch, processed)
    if processed then
        return
    end
    
    local up = wheel >= 0;
    print(if up then "Up!" else "Down!")
end)

-- Method 2, allows for keeping pointer logic coupled.
UserInputService.InputChanged:Connect(function(input, processed)
    if processed or input.UserInputType ~= Enum.UserInputType.MouseWheel then
        return
    end

    local up = input.Position.Z >= 0
    print(if up then "Up!" else "Down!")
end)