# Mouse wheel {% hint style="info" %} This wiki is now **archived**. You should instead visit the [Linebender wiki](https://linebender.org/wiki/) at {% endhint %} What does scrolling actually mean? It depends on the platform and on the mouse. See [druid#68](https://github.com/xi-editor/druid/pull/68) for the code that implements this. There are some additional links and comments in the review. ## Web [W3C's WheelEvent](https://w3c.github.io/uievents/#event-type-wheel) specifies it as the “expected amount the page will scroll” On my Windows machine, “away from user” is a negative number. At lines = 3 (in preferences), one bump of the physical mouse wheel is 200. Rightward motion on the trackpad is a positive number. On my Mac, when “Scroll direction: Natural” is checked, “away from user” is a positive number, and rightward motion on the trackpad is a negative number. Both flip when it is unchecked. The magnitude is dependent on the rate of scrolling (i.e. this is adaptively scaled). See significant discussion in [Chromium issue 227454](https://bugs.chromium.org/p/chromium/issues/detail?id=227454), including having got the polarity wrong. ## Windows [The doc for WM\_MOUSEWHEEL message](https://docs.microsoft.com/en-us/windows/win32/inputdev/wm-mousewheel) specifies that rolling away from the user is a positive number. Rightward motion on the trackpad is a positive number. One bump of the external scroll wheel is 120, consistent with documentation. The sensitivity setting should be read from `SystemParametersInfo`. ## macOS [The doc for NSEvent scrollingDeltaY](https://developer.apple.com/documentation/appkit/nsevent/1535387-scrollingdeltay) is not helpful. The value of `scrollingDeltaX` and `scrollingDeltaY` is the negative of the web value. Note also, `hasPreciseScrollingDeltas` is true for trackpad and false for external mice. The value of `scrollingDeltaX` and `scrollingDeltaY` inverts when the “Scroll direction: Natural” setting is toggled, i.e .the setting is applied before the event is given to the app. ## External mouse wheel vs trackpad An external mouse wheel delta is traditionally multiplied by 32, while a touchpad delta is not. Here's the [corresponding Makepad version](https://github.com/makepad/makepad/blob/07f1e72ba19f327d56c6bdfe4211358b2aaee006/render/src/cx_cocoa.rs#L333). Also note that [Winit keeps the distinction](https://github.com/rust-windowing/winit/blob/34db2d7d4c1deebbb706194113853591e7c6b60c/src/event.rs#L360) (using LineDelta for an ext mouse wheel, PixelDelta for the trackpad). {% hint style="info" %} This wiki is now **archived**. You should instead visit the [Linebender wiki](https://linebender.org/wiki/) at {% endhint %} --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://linebender.gitbook.io/linebender-graphics-wiki/mouse-wheel.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.