Bugzilla

(In reply to Mike Conley (:mconley) (:⚙️) from comment #3)
> is there something that the front-end should do to support this new high-resolution scroll support for Wayland?

I don't have a hi-res mouse to test with unfortunately, but looking at what I believe is the [relevant code](https://searchfox.org/mozilla-central/rev/8f423e3c79147c65d078589f3666dd25ffe80840/toolkit/content/widgets/tabbox.js#453-462) in the frontend, my guess is that we need to upgrade this event listener from being a `DOMMouseScroll` listener to being a `wheel` listener.

`DOMMouseScroll` is a legacy event type that does not play well with smooth / continuous scrolling devices such as touchpads and hi-resolution mice, because its "delta" is represented as an integer number of lines, and these devices can produce scrolling by amounts which are a fraction of a line. (Bug 1705584 is another example of the sort of issue this can cause.) `wheel` does not have this problem since it supports a `double` delta value, as well as a pixel delta mode.

The part I'm not sure about, and which likely requires having a hi-res mouse to play around with, is what sort of check we need on the `delta` of the wheel event to ensure we only scroll one tab per wheel tick.

Mike, I'm going to bounce this back to you for now, maybe the above is enough to go on (e.g. maybe there are existing listeners in the front-end for `wheel` events that we can model this one on). Maybe Martin has a hi-res mouse available to test a potential patch with. (I'll also see about trying to acquire one for the Toronto office for future testing purposes.)

(In reply to Mike Conley (:mconley) (:⚙️) from comment #3)
> is there something that the front-end should do to support this new high-resolution scroll support for Wayland?

I don't have a hi-res mouse to test with unfortunately, but looking at what I believe is the [relevant code](https://searchfox.org/mozilla-central/rev/8f423e3c79147c65d078589f3666dd25ffe80840/toolkit/content/widgets/tabbox.js#453-462) in the frontend, my guess is that we need to upgrade this event listener from being a `DOMMouseScroll` listener to being a `wheel` listener.

`DOMMouseScroll` is a legacy event type that does not play well with smooth / continuous scrolling devices such as touchpads and hi-resolution mice, because its "delta" is represented as an integer number of lines, and these devices can produce scrolling by amounts which are a fraction of a line. (Bug 1705584 is another example of the sort of issue this can cause.) `wheel` does not have this problem since it supports a `double` delta value, as well as a pixel delta mode.

The part I'm not sure about, and which likely requires having a hi-res mouse to play around with, is what sort of check we need on the `delta` of the wheel event to ensure we only scroll one tab per wheel tick.

Mike, I'm going to bounce this back to you for now, maybe the above is enough to go on (e.g. maybe there are existing listeners in the front-end for `wheel` events that we can model this one on). Maybe Martin has a hi-res mouse available to test a potential patch with. (I'll also see about acquiring one for the Toronto office for future testing purposes.)