How to handle MouseWheel when both pixel and line deltas are available ?

[elinorbgr]

In some cases (if the compositor supports it), the wayland backend can have access to both LineDelta and PixelDelta values for a given scroll event.

In this case, what should be done ?

• generate only the PixelDelta event ?
• generate only the LineDelta event ?
• generate both ?
• modify the MouseWheel event so that it may provide both values ?

[nixpulvis]

Two questions.

1. Why even have two kinds of events? Couldn't everything be a normalized PixelDelta? Alacritty already converts to pixels (and then to proper lines) internally. What devices should I expect to see PixelDelta on exactly? Even my continuous trackpad, and trackpoint return fractional LineDeltas.

2. Assuming we don't want to merge these two events, or that there's value in exposing the resolution of a single mouse scroll "click". Wouldn't a better name for this be something like ClickDelta, since as far as I understand this, there's nothing related to "lines" of text needed here. I could for example have a single "click" be used to fire a gun in an FPS for example (ah the best cheat code, sorry I digress), which has nothing to do with a "line" of any kind.

[kchibisov]

What devices should I expect to see PixelDelta on exactly?

Mostly touchpads and I guess drawing tablets? For example my mouse is sending LineDelta, but touchpad is sending PixelDelta. However it depends on device most of the time.

[akhilman]

Post explaining why there are two (actually three) different delta types: http://who-t.blogspot.com/2015/01/providing-physical-movement-of-wheel.html
So basically yes, touchpads and tablets use pixels, but the mouse counts the number of clicks and degrees.