Vim preview window.vim

au! CursorHold *.[ch] nested call PreviewWord()
func PreviewWord()
    if &previewwindow                  " don't do this in the preview window
        return
    endif
    let w = expand("<cword>")          " get the word under cursor
    if w =~ '\a'                       " if the word contains a letter

        " Delete any existing highlight before showing another tag
        silent! wincmd P                 " jump to preview window
        if &previewwindow                        " if we really get there...
            match none                     " delete existing highlight
            wincmd p                       " back to old window
        endif

        " Try displaying a matching tag for the word under the cursor
        try
            exe "ptag " . w
        catch
            return
        endtry

        silent! wincmd P                 " jump to preview window
        if &previewwindow                " if we really get there...
            if has("folding")
                silent! .foldopen            " don't want a closed fold
            endif
            call search("$", "b")          " to end of previous line
            let w = substitute(w, '\\', '\\\\', "")
            call search('\<\V' . w . '\>') " position cursor on match
            " Add a match highlight to the word at this position
            hi previewWord term=bold ctermfg=red guibg=NONE
            exe 'match previewWord "\%' . line(".") . 'l\%' . col(".") . 'c\k*"'
            wincmd p                       " back to old window
        endif
    endif
endfun
set previewheight=20
set updatetime=500