05-03-26

Brush Size Control with Scroll Wheel

This Lua script for Rebind hardware input allows you to control brush size in drawing applications using your scroll wheel. Hold a modifier key and scroll to adjust the brush size, enhancing your work

rebindlua scriptbrush sizescroll wheeldrawinginputhardware input

Question

How can I control brush size with the scroll wheel in drawing applications?

Rebind AI

Here's a script that allows you to control brush size using the scroll wheel while holding a modifier key (default: Left Alt). It works by sending Ctrl+Scroll events, which is a common shortcut for brush size adjustment in many drawing applications.

lua

-- rebind: name=Brush Size Control
-- rebind: description=Scroll wheel adjusts brush size in drawing apps

local cfg = UI.Schema({
    modifier = UI.Keybind("LAlt", { label = "Modifier Key", tooltip = "Hold this key while scrolling" }),
    step_size = UI.Slider(1, { min = 1, max = 10, label = "Step Size", suffix = "px" }),
})

function OnScroll(delta)
    if not Input.IsDown(cfg.modifier) then
        return true
    end

    -- Hold Ctrl and scroll to adjust brush size
    -- Most drawing apps (Photoshop, Krita, Clip Studio, etc.) use this
    HID.Down("LCtrl")
    HID.Scroll(delta * cfg.step_size)
    HID.Up("LCtrl")

    return false
end

How it works:

When you hold the modifier key (default Alt) and scroll your mouse wheel, the script intercepts the scroll event and converts it to Ctrl+Scroll. Most drawing applications interpret Ctrl+Scroll as "change brush size":

Scroll up → increase brush size
Scroll down → decrease brush size

The step_size slider lets you control the sensitivity — higher values make the brush size change more dramatically per scroll notch.

Compatible apps:

Photoshop
Krita
Clip Studio Paint
Procreate Dreams
GIMP
Paint Tool SAI
Aseprite
Autodesk Sketchbook

You can customize the modifier key to use Shift, Ctrl, or any other key, depending on your drawing app's hotkey preferences.

Learn more: