fontresize.vim

command! -nargs=0 -bar FontReSize call s:changeFontSize()
function! s:changeFontSize()
    let font_size_pat = '(.{-}\S:h)(\d+\.?\d*)(.{-})'
    let valid_num_pat = '\d+(\.(0|5))?'
    let current_font_size = substitute(&guifont, '\v^' . font_size_pat . '$', '\2', '')
    if current_font_size  !~ '\v^' . valid_num_pat . '$'
        return
    endif

    " disalbe ime
    let default_im_insert = &iminsert
    let &iminsert = 0
    let default_im_disable = &imdisable
    let &imdisable = 1

    while 1
        let l:input = input("\press esc to exit\n", '')

        if l:input =~ '\v^(\+|-)$'
            let new_font_size = string(eval(current_font_size) + (l:input == '+' ? +0.5 : -0.5))
        elseif l:input =~ '\v^(\+|-)' . valid_num_pat . '$'
            let new_font_size = string(eval(current_font_size) + eval(l:input))
        elseif l:input =~ '\v^' . valid_num_pat . '$'
            let new_font_size = l:input
        elseif l:input == ''
            break
        else
            echo "\nInvalid Input"
            continue
        endif
        if eval(new_font_size) > 0.5 && new_font_size =~ '\v^' . valid_num_pat .  '$'
            let &guifont     = substitute(&guifont,     '\v(^|,)' . font_size_pat . '(,|$)', '\2' . new_font_size . '\4', 'g')
            let &guifontwide = substitute(&guifontwide, '\v(^|,)' . font_size_pat . '(,|$)', '\2' . new_font_size . '\4', 'g')
            let current_font_size = new_font_size
            redraw
        endif
    endwhile

    let &iminsert = default_im_insert
    let &imdisable = default_im_disable
endfunction