How can I use my trackpad for horizontal scrolling?

Question

I just noticed that my trackpad scroll works in Vim, inertia and all. I'd like to change this to work horizontally - so I can scroll up and down to make the cursor move left-and-right instead of holding down the right arrow key for huge amounts of time.

How can I map my scrolling to left/right movement?

Answer 1

According to :help scroll-mouse-wheel the answer is no if you are using the Win32 GUI.

On the other hand, using X11 GUI or console vim with mouse support, the wheel sends key presses that you can remap.

So, you could get the behaviour you describe by

:nmap <ScrollWheelUp> h
:nmap <ScrollWheelDown> l

Note that I'm using nmap for mapping in normal mode.

To get similar behaviour in other modes, you can map to the direction instead of the normal key. E.g. for insert mode movement:

:imap <ScrollWheelUp> <Left>
:imap <ScrollWheelDown> <Right>

To make these default, stick them at the bottom of your vimrc.

Answer 2

I figured out a way to do that with Hammerspoon and clever usage of mapping.

The first part is configuring Shift + ScrollUp and Shift + ScrollDown to scroll horizontally. In order to do that, you have put the following code snippet in your .vimrc:

nnoremap <S-ScrollWheelUp> <ScrollWheelLeft>
nnoremap <S-2-ScrollWheelUp> <2-ScrollWheelLeft>
nnoremap <S-3-ScrollWheelUp> <3-ScrollWheelLeft>
nnoremap <S-4-ScrollWheelUp> <4-ScrollWheelLeft>
nnoremap <S-ScrollWheelDown> <ScrollWheelRight>
nnoremap <S-2-ScrollWheelDown> <2-ScrollWheelRight>
nnoremap <S-3-ScrollWheelDown> <3-ScrollWheelRight>
nnoremap <S-4-ScrollWheelDown> <4-ScrollWheelRight>

Note that we have to use <S-2-ScrollWheelUp> and the like because they are sent as keys to the terminal as well. I found no documentation about this (I figured this out by using Ctrl + V while scrolling in insert mode).

After that, we have to remap horizontal scrolls to Shift + vertical scrolls. To do so, we place the following snippet in Hammerspoon's init.lua

scrollBind = hs.eventtap.new({hs.eventtap.event.types.scrollWheel}, function(e)
  if is_active('iTerm2') then
    local horizontalOffset = e:getProperty(hs.eventtap.event.properties.scrollWheelEventDeltaAxis2)

    if horizontalOffset ~= 0 then
      hs.eventtap.scrollWheel({ 0, horizontalOffset }, {"shift"}, 'pixel')
      return true
    end
  end

  return false
end):start()

function is_active(program_name)
  local active_window_name = hs.window.focusedWindow():application():name()
  return active_window_name == program_name
end

We create the scrollBind variable just so the keystroke watcher isn't erased by the Lua's garbage collector.

Answer 3

If you use MacVim on OS X, this will work with a trackpad:

set mouse=n " enable mouse in normal mode
set nowrap  " disable line wrapping (so there's something to scroll to)