[Wayland-bugs] [Bug 101141] Proposal for libinput mouse wheel acceleration

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=101141

            Bug ID: 101141
           Summary: Proposal for libinput mouse wheel acceleration
           Product: Wayland
           Version: unspecified
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: libinput
          Assignee: wayland-bugs at lists.freedesktop.org
          Reporter: adam at spicenitz.org

Let me start with this proposal for mouse wheel acceleration in libinput.

Use case:
- Scrolling through a long document is slow with a mouse wheel

Prior work showing benefits of wheel acceleration:
- macOS
- Chrome OS

Requirements:
- Don't break anything
- Require minimum changes from clients

Proposal:
- Mouse wheel acceleration at the libinput level, only for mouse wheels
- Do no acceleration on values returned from
libinput_event_pointer_get_axis_value_discrete, this keeps the promise in the
API of reporting "physical mouse wheel clicks" and keeps us from needing to
implement a new "get unaccelerated" API
- Ensure that legacy X wheel events (pre-XI2.1) are not accelerated

Open questions:
- Does this cover enough clients without breaking things? Chrome and Firefox
support XI2.1, so this would accelerate those programs.
- Under X or XWayland, is it possible to accelerate XI2.1 events but not the
legacy events? Or are the legacy events generated automatically?
- Or is it ok to accelerate legacy X wheel events? emacs has scroll
acceleration already, and other clients may as well.

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