There are two methods I know of. Add these lines to your .vimrc file (selecting only one of the two methods):
Method 1:
function! s:GetNumScroll(num)
let num_rows = winheight(0)
let num_scroll = a:num
if (a:num == -1)
let num_scroll = (num_rows + 1) / 2
elseif (a:num == -2)
let num_scroll = num_rows
endif
if (num_scroll < 1)
let num_scroll = 1
endif
return num_scroll
endfunction
function! s:RtrnToOrig(before_scr_line)
normal H
let delta = a:before_scr_line - winline()
while (delta != 0)
if (delta < 0)
let delta = winline() - a:before_scr_line
let iter = 1
while (iter <= delta)
execute "normal" "gk"
let iter +=1
endwhile
elseif (delta > 0)
let iter = 1
while (iter <= delta)
execute "normal" "gj"
let iter +=1
endwhile
endif
let delta = a:before_scr_line - winline()
endwhile
endfunction
function! s:scrollUP(num)
let num_scroll = <SID>GetNumScroll(a:num)
let num_rows = winheight(0)
" -------------
let before_scr_line = winline()
normal L
let after_scr_line = winline()
let extra = num_rows - after_scr_line
let extra += num_scroll
" move by 1 to prevent over scrolling
let iter = 1
while (iter <= extra)
execute "normal" "gj"
let iter +=1
endwhile
" -------------
call <SID>RtrnToOrig(before_scr_line)
endfunction
function! s:scrollDN(num)
let num_scroll = <SID>GetNumScroll(a:num)
" -------------
let before_scr_line = winline()
normal H
let after_scr_line = line(".")
execute "normal" "gk"
let after_scr2_line = line(".")
if ( (after_scr_line == after_scr2_line) && (after_scr_line > 1) )
execute "normal" "gk"
endif
let extra = (num_scroll - 1)
let extra += (winline() - 1)
" move by 1 to prevent over scrolling
let iter = 1
while (iter <= extra)
execute "normal" "gk"
let iter +=1
endwhile
" -------------
call <SID>RtrnToOrig(before_scr_line)
endfunction
nmap <silent> <C-J> :call <SID>scrollUP(1)<CR>
nmap <silent> <C-K> :call <SID>scrollDN(1)<CR>
nmap <silent> <C-F> :call <SID>scrollUP(-1)<CR>
nmap <silent> <C-B> :call <SID>scrollDN(-1)<CR>
nmap <silent> <PageDown>:call <SID>scrollUP(-2)<CR>
nmap <silent> <PageUp> :call <SID>scrollDN(-2)<CR>
This uses the normal H, L to go to screen top, bot and the gk, gj commands to move up, down by screen line instead of actual line. Its more complicated than would seem needed just to work correctly when lines are longer than the screen width and wordwrap is on.
Or this method (which has previously been posted in vim tips wiki and on Stack Exchange):
Method 2:
" N<C-D> and N<C-U> idiotically change the scroll setting
function! s:Saving_scrollV(cmd)
let save_scroll = &scroll
execute "normal" a:cmd
let &scroll = save_scroll
endfunction
" move and scroll
nmap <silent> <C-J> :call <SID>Saving_scrollV("1<C-V><C-D>")<CR>
vmap <silent> <C-J> <Esc> :call <SID>Saving_scrollV("gv1<C-V><C-D>")<CR>
nmap <silent> <C-K> :call <SID>Saving_scrollV("1<C-V><C-U>")<CR>
vmap <silent> <C-K> <Esc> :call <SID>Saving_scrollV("gv1<C-V><C-U>")<CR>
nmap <silent> <C-F> :call <SID>Saving_scrollV("<C-V><C-D>")<CR>
vmap <silent> <C-F> <Esc> :call <SID>Saving_scrollV("gv<C-V><C-D>")<CR>
nmap <silent> <PageDown> :call <SID>Saving_scrollV("<C-V><C-D>")<CR>
vmap <silent> <PageDown> <Esc>:call <SID>Saving_scrollV("gv<C-V><C-D>")<CR>
nmap <silent> <C-B> :call <SID>Saving_scrollV("<C-V><C-U>")<CR>
vmap <silent> <C-B> <Esc> :call <SID>Saving_scrollV("gv<C-V><C-U>")<CR>
nmap <silent> <PageUp> :call <SID>Saving_scrollV("<C-V><C-U>")<CR>
vmap <silent> <PageUp> <Esc> :call <SID>Saving_scrollV("gv<C-V><C-U>")<CR>
The only issue I have with the second method is when lines are longer than the screen width and wordwrap is on then the cursor can move up or down some to account for the extra lines from the wrap. Also at the very top and bottom of the file the cursor can move. The first method really attempts to never move the cursor in all cases.