csapprox/plugin/CSApprox.vim

" CSApprox:    Make gvim-only colorschemes work transparently in terminal vim
" Maintainer:  Matthew Wozniski (mjw@drexel.edu)
" Date:        Sun, 05 Oct 2008 00:26:22 -0400
" Version:     1.00
" History:     :help csapprox-changelog

" Whenever you change colorschemes using the :colorscheme command, this script
" will be executed.  If you're running in 256 color terminal or an 88 color
" terminal, as reported by the command ":set t_Co?", it will take the colors
" that the scheme specified for use in the gui and use an approximation
" algorithm to try to gracefully degrade them to the closest color available.
" If you are running in a gui or if t_Co is reported as less than 88 colors,
" no changes are made.  Also, no changes will be made if the colorscheme seems
" to have been high color already.

" {>1} Basic plugin setup

" {>2} Check preconditions
" Quit if the user doesn't want or need us or is missing the gui feature.  We
" need +gui to be able to check the gui color settings; vim doesn't bother to
" store them if it is not built with +gui.
if has("gui_running") || ! has("gui") || exists('g:CSApprox_loaded')
  " XXX This depends upon knowing the default for g:CSApprox_verbose_level
  let s:verbose = 1
  if exists("g:CSApprox_verbose_level")
    let s:verbose  = g:CSApprox_verbose_level
  endif

  if has('gui_running') && s:verbose > 1
    echomsg "Not loading CSApprox in gui mode."
  elseif ! has('gui') && s:verbose > 0
    echomsg "CSApprox needs gui support - not loading."
  endif

  unlet s:verbose

  finish
endif

" {1} Mark us as loaded, and disable all compatibility options for now.
let g:CSApprox_loaded = 1

let s:savecpo = &cpo
set cpo&vim

" {>1} Built-in approximation algorithm

" {>2} Cube definitions
let s:xterm_colors   = [ 0x00, 0x5F, 0x87, 0xAF, 0xD7, 0xFF ]
let s:eterm_colors   = [ 0x00, 0x2A, 0x55, 0x7F, 0xAA, 0xD4 ]
let s:konsole_colors = [ 0x00, 0x33, 0x66, 0x99, 0xCC, 0xFF ]
let s:xterm_greys    = [ 0x08, 0x12, 0x1C, 0x26, 0x30, 0x3A,
                       \ 0x44, 0x4E, 0x58, 0x62, 0x6C, 0x76,
                       \ 0x80, 0x8A, 0x94, 0x9E, 0xA8, 0xB2,
                       \ 0xBC, 0xC6, 0xD0, 0xDA, 0xE4, 0xEE ]

let s:urxvt_colors   = [ 0x00, 0x8B, 0xCD, 0xFF ]
let s:urxvt_greys    = [ 0x2E, 0x5C, 0x73, 0x8B,
                       \ 0xA2, 0xB9, 0xD0, 0xE7 ]

" {>2} Integer comparator
" Used to sort the complete list of possible colors
function! s:IntCompare(i1, i2)
  return a:i1 == a:i2 ? 0 : a:i1 > a:i2 ? 1 : -1
endfunc

" {>2} Approximator
" Takes 3 decimal values for r, g, and b, and returns the closest cube number.
" Uses &term to determine which cube should be used, though if &term is set to
" "xterm" the variables g:CSApprox_eterm and g:CSApprox_konsole can be used to
" change the default palette.
"
" This approximator considers closeness based upon the individiual components.
" For each of r, g, and b, it finds the closest cube component available on
" the cube.  If the three closest matches can combine to form a valid color,
" this color is used, otherwise we repeat the search with the greys removed,
" meaning that the three new matches must make a valid color when combined.
function! s:ApproximatePerComponent(r,g,b)
  let hex = printf("%02x%02x%02x", a:r, a:g, a:b)

  let greys  = (&t_Co == 88 ? s:urxvt_greys : s:xterm_greys)

  if &t_Co == 88
    let colors = s:urxvt_colors
    let type = 'urxvt'
  elseif ((&term ==# 'xterm' || &term =~# '^screen')
       \   && exists('g:CSApprox_konsole'))
       \ || &term =~? '^konsole'
    let colors = s:konsole_colors
    let type = 'konsole'
  elseif ((&term ==# 'xterm' || &term =~# '^screen')
       \   && exists('g:CSApprox_eterm'))
       \ || &term =~? '^eterm'
    let colors = s:eterm_colors
    let type = 'eterm'
  else
    let colors = s:xterm_colors
    let type = 'xterm'
  endif

  if !exists('s:approximator_cache_'.type)
    let s:approximator_cache_{type} = {}
  endif

  let rv = get(s:approximator_cache_{type}, hex, -1)
  if rv != -1
    return rv
  endif

  " Only obtain sorted list once
  if !exists("s:".type."_greys_colors")
    let s:{type}_greys_colors = sort(greys + colors, "s:IntCompare")
  endif

  let greys_colors = s:{type}_greys_colors

  let r = s:NearestElemInList(a:r, greys_colors)
  let g = s:NearestElemInList(a:g, greys_colors)
  let b = s:NearestElemInList(a:b, greys_colors)

  let len = len(colors)
  if (r == g && g == b && index(greys, r) > 0)
    let rv = 16 + len * len * len + index(greys, r)
  else
    let r = s:NearestElemInList(a:r, colors)
    let g = s:NearestElemInList(a:g, colors)
    let b = s:NearestElemInList(a:b, colors)
    let rv = index(colors, r) * len * len
         \ + index(colors, g) * len
         \ + index(colors, b)
         \ + 16
  endif

  let s:approximator_cache_{type}[hex] = rv
  return rv
endfunction

" {>2} Color comparator
" Finds the nearest element to the given element in the given list
function! s:NearestElemInList(elem, list)
  let len = len(a:list)
  for i in range(len-1)
    if (a:elem <= (a:list[i] + a:list[i+1]) / 2)
      return a:list[i]
    endif
  endfor
  return a:list[len-1]
endfunction

" {>1} Collect info for the set highlights

" {>2} Determine if synIDattr is usable
" As of 7.2.018, synIDattr() can't be used to check 'guisp', and no official
" patch has been released despite my suggesting one.  So, in an attempt to be
" forward compatible, I've included a test to see if synIDattr() works
" properly.  If synIDattr() works properly, we'll use it to check the 'guisp'
" attribute, otherwise we'll fall back onto using :redir and checking the
" output of :highlight.  This test can be overridden by setting the global
" variable g:CSApprox_redirfallback to 1 (to force use of :redir) or to 0 (to
" force use of synIDattr()).
function! s:NeedRedirFallback()
  if !exists("g:CSApprox_redirfallback")
    hi CSApproxTest guisp=Red gui=standout
    if synIDattr(hlID('CSApproxTest'), 'sp', 'gui') == '1'
      " We requested the 'sp' attribute, but vim thought we wanted 'standout'
      " So, reporting of the guisp attribute is broken.  Fall back on :redir
      let g:CSApprox_redirfallback=1
    else
      " Reporting guisp works, use synIDattr
      let g:CSApprox_redirfallback=0
    endif
  endif
  return g:CSApprox_redirfallback
endfunction

" {>2} Collect and store the highlights
" Get a dictionary containing information for every highlight group not merely
" linked to another group.  Return value is a dictionary, with highlight group
" numbers for keys and values that are dictionaries with four keys each,
" 'name', 'term', 'cterm', and 'gui'.  'name' holds the group name, and each
" of the others holds highlight information for that particular mode.
function! s:Highlights()
  let rv = {}

  let i = 0
  while 1
    let i += 1

    " Only interested in groups that exist and aren't linked
    if synIDtrans(i) == 0
      break
    endif

    " Handle vim bug allowing groups with name == "" to be created
    if synIDtrans(i) != i || len(synIDattr(i, "name")) == 0
      continue
    endif

    let rv[i] = {}
    let rv[i].name = synIDattr(i, "name")

    for where in [ "term", "cterm", "gui" ]
      let rv[i][where]  = {}
      for attr in [ "fg", "bg", "sp", "bold", "italic",
            \ "reverse", "underline", "undercurl" ]
        let rv[i][where][attr] = synIDattr(i, attr, where)
      endfor

      if s:NeedRedirFallback()
        redir => temp
        exe 'sil hi ' . rv[i].name
        redir END
        let temp = matchstr(temp, where.'sp=\zs.*')
        if len(temp) == 0 || temp[0] =~ '\s'
          let temp = ""
        else
          " Make sure we can handle guisp='dark red'
          let temp = substitute(temp, '[\x00].*', '', '')
          let temp = substitute(temp, '\s*\(c\=term\|gui\).*', '', '')
          let temp = substitute(temp, '\s*$', '', '')
        endif
        let rv[i][where]["sp"] = temp
      endif
    endfor
  endwhile

  return rv
endfunction

" {>1} Handle color names

" Place to store rgb.txt name to color mappings - lazy loaded if needed
let s:rgb = {}

" {>2} Builtin gui color names
" gui_x11.c and gui_gtk_x11.c have some default colors names that are searched
" if a color is not in rgb.txt. We'll pretend they're in rgb.txt with these
" values, and overwrite them with a different value if we find them...
let s:rgb_defaults = { "lightred"     : "#FFBBBB",
                     \ "lightgreen"   : "#88FF88",
                     \ "lightmagenta" : "#FFBBFF",
                     \ "darkcyan"     : "#008888",
                     \ "darkblue"     : "#0000BB",
                     \ "darkred"      : "#BB0000",
                     \ "darkmagenta"  : "#BB00BB",
                     \ "darkgrey"     : "#BBBBBB",
                     \ "darkyellow"   : "#BBBB00",
                     \ "gray10"       : "#1A1A1A",
                     \ "grey10"       : "#1A1A1A",
                     \ "gray20"       : "#333333",
                     \ "grey20"       : "#333333",
                     \ "gray30"       : "#4D4D4D",
                     \ "grey30"       : "#4D4D4D",
                     \ "gray40"       : "#666666",
                     \ "grey40"       : "#666666",
                     \ "gray50"       : "#7F7F7F",
                     \ "grey50"       : "#7F7F7F",
                     \ "gray60"       : "#999999",
                     \ "grey60"       : "#999999",
                     \ "gray70"       : "#B3B3B3",
                     \ "grey70"       : "#B3B3B3",
                     \ "gray80"       : "#CCCCCC",
                     \ "grey80"       : "#CCCCCC",
                     \ "gray90"       : "#E5E5E5",
                     \ "grey90"       : "#E5E5E5" }

" {>2} Find and parse rgb.txt
" Search for an rgb.txt in a set of default directories.  If the user wishes
" to override the default search path, he can specify a list of other
" directories to search first in g:CSApprox_extra_rgb_txt_dirs.  When rgb.txt
" has been located, and verified to be good (by having enough non-blank
" non-comment correctly formatted lines), the parsed information is stored to
" the dictionary s:rgb - the keys are color names (in lowercase), the values
" are strings representing color values (as '#rrggbb').
function! s:UpdateRgbHash()
  " Pattern for ignored lines - all blanks, or blanks then !
  let ignorepat = '^\s*\%(!.*\)\=$'
  " fmt is (blanks?)(red)(blanks)(green)(blanks)(blue)(blanks)(name)
  let parsepat  = '^\s*\(\d\+\)\s\+\(\d\+\)\s\+\(\d\+\)\s\+\(.*\)$'

  let user = []
  if exists("g:CSApprox_extra_rgb_txt_dirs")
    if type(g:CSApprox_extra_rgb_txt_dirs) == type([])
      let user = g:CSApprox_extra_rgb_txt_dirs
    else
      let user = [ g:CSApprox_extra_rgb_txt_dirs ]
    endif
  endif

  for dir in user + [ '/usr/local/share/X11',
                    \ '/usr/share/X11',
                    \ '/etc/X11',
                    \ '/usr/local/lib/X11',
                    \ '/usr/lib/X11',
                    \ '/usr/local/X11R6/lib/X11',
                    \ '/usr/X11R6/lib/X11' ]
    let s:rgb = copy(s:rgb_defaults)
    sil! let lines = readfile(dir . '/rgb.txt')

    for line in lines
      if line =~ ignorepat
        continue " Line is blank, entirely spaces, or a comment
      endif
      let v = matchlist(line, parsepat)
      if len(v) > 0
        let s:rgb[tolower(v[4])] = printf("#%02x%02x%02x", v[1], v[2], v[3])
      endif
    endfor

    if len(s:rgb) > 50
      return 0 " Long enough, must have been valid
    endif
  endfor

  let s:rgb = {}
  throw "Failed to find a valid rgb.txt!"
endfunction

" {>1} Derive and set cterm attributes

" {>2} Attribute overrides
" Allow the user to override a specified attribute with another attribute.
" For example, the default is to map 'italic' to 'underline' (since many
" terminals cannot display italic text, and gvim itself will replace italics
" with underlines where italicizing is impossible), and to replace 'sp' with
" 'fg' (since terminals can't use one color for the underline and another for
" the foreground, we color the entire word).  This default can of course be
" overridden by the user, by setting g:CSApprox_attr_map.  This map must be
" a dictionary of string keys, representing the same attributes that synIDattr
" can look up, to string values, representing the attribute mapped to or an
" empty string to disable the given attribute entirely.
function! s:attr_map(attr)
  let attr = tolower(a:attr)

  if attr == 'inverse'
    let attr = 'reverse'
  endif

  let valid_attrs = [ 'bg', 'fg', 'sp', 'bold', 'italic',
                    \ 'reverse', 'underline', 'undercurl' ]

  if index(valid_attrs, attr) == -1
    throw "Looking up invalid attribute '" . attr . "'"
  endif

  if !exists("g:CSApprox_attr_map") || type(g:CSApprox_attr_map) != type({})
    let g:CSApprox_attr_map = { 'italic' : 'underline', 'sp' : 'fg' }
  endif

  let rv = get(g:CSApprox_attr_map, attr, attr)

  if index(valid_attrs, rv) == -1 && rv != ''
    " The user mapped 'attr' to something invalid
    throw "Bad attr map: '" . attr . "' to unknown attribute '" . rv . "'"
  endif

  let colorattrs = [ 'fg', 'bg', 'sp' ]
  if rv != '' && !!(index(colorattrs, attr)+1) != !!(index(colorattrs, rv)+1)
    " The attribute the user mapped to was valid, but of a different type.
    throw "Bad attr map: Can't map color attr to boolean (".attr."->".rv.")"
  endif

  if rv == 'inverse'
    let rv = 'reverse' " Internally always use 'reverse' instead of 'inverse'
  elseif rv == 'sp'
    " Terminals can't handle the guisp attribute; disable it if it was left on
    let rv = ''
  endif

  return rv
endfunction

" {>2} Map gui settings to cterm settings
" Given information about a highlight group, replace the cterm settings with
" the mapped gui settings, applying any attribute overrides along the way.  In
" particular, this gives special treatment to the 'reverse' attribute and the
" 'guisp' attribute.  In particular, if the 'reverse' attribute is set for
" gvim, we unset it for the terminal and instead set ctermfg to match guibg
" and vice versa, since terminals can consider a 'reverse' flag to mean using
" default-bg-on-default-fg instead of current-bg-on-current-fg.  We also
" ensure that the 'sp' attribute is never set for cterm, since no terminal can
" handle that particular highlight.  If the user wants to display the guisp
" color, he should map it to either 'fg' or 'bg' using g:CSApprox_attr_map.
function! s:FixupCtermInfo(hl)
  let hl = a:hl

  " Find attributes to be set in the terminal
  for attr in [ "bold", "italic", "reverse", "underline", "undercurl" ]
    let hl.cterm[attr] = ''
    if hl.gui[attr] == 1
      if s:attr_map(attr) != ''
        let hl.cterm[ s:attr_map(attr) ] = 1
      endif
    endif
  endfor

  for color in [ "bg", "fg" ]
    let eff_color = color
    if hl.cterm['reverse']
      let eff_color = (color == 'bg' ? 'fg' : 'bg')
    endif

    let hl.cterm[color] = get(hl.gui, s:attr_map(eff_color), '')
  endfor

  if hl.gui['sp'] != '' && s:attr_map('sp') != ''
    let hl.cterm[s:attr_map('sp')] = hl.gui['sp']
  endif

  if hl.cterm['reverse'] && hl.cterm.bg == ''
    let hl.cterm.bg = 'fg'
  endif

  if hl.cterm['reverse'] && hl.cterm.fg == ''
    let hl.cterm.fg = 'bg'
  endif

  if hl.cterm['reverse']
    let hl.cterm.reverse = ''
  endif
endfunction

" {>2} Set cterm colors for a highlight group
" Given the information for a single highlight group (ie, the value of
" one of the items in s:Highlights()), uses s:FixupCtermInfo to parse the
" structure and normalize it for use on a cterm, then handles matching the
" gvim colors to the closest cterm colors by calling the approximator
" specified with g:CSApprox_approximator_function and sets the colors and
" attributes appropriately to match the gui.
function! s:SetCtermFromGui(hl)
  let hl = a:hl

  call s:FixupCtermInfo(hl)

  " Set up the default approximator function, if needed
  if !exists("g:CSApprox_approximator_function")
    let g:CSApprox_approximator_function=function("s:ApproximatePerComponent")
  endif

  " Clear existing highlights
  exe 'hi ' . hl.name . ' cterm=NONE ctermbg=NONE ctermfg=NONE'

  for which in [ 'bg', 'fg' ]
    let val = hl.cterm[which]

    " Skip unset colors
    if val == -1 || val == ""
      continue
    endif

    " Try translating anything but 'fg', 'bg', #rrggbb, and rrggbb from an
    " rgb.txt color to a #rrggbb color
    if val !~? '^[fb]g$' && val !~ '^#\=\x\{6}$'
      if empty(s:rgb)
        call s:UpdateRgbHash()
      endif
      try
        let val = s:rgb[tolower(val)]
      catch /^/
        if &verbose
          echomsg "CSApprox: Colorscheme uses unknown color \"" . val . "\""
        endif
        continue
      endtry
    endif

    if val =~? '^[fb]g$'
      exe 'hi ' . hl.name . ' cterm' . which . '=' . val
      let hl.cterm[which] = val
    elseif val =~ '^#\=\x\{6}$'
      let val = substitute(val, '^#', '', '')
      let r = str2nr(val[0] . val[1], 16)
      let g = str2nr(val[2] . val[3], 16)
      let b = str2nr(val[4] . val[5], 16)
      let hl.cterm[which] = g:CSApprox_approximator_function(r, g, b)
      exe 'hi ' . hl.name . ' cterm' . which . '=' . hl.cterm[which]
    else
      throw "Internal error handling color: " . val
    endif
  endfor

  " Finally, set the attributes
  let attributes = []
  for attribute in [ 'bold', 'italic', 'underline', 'undercurl' ]
    if hl.cterm[attribute] == 1
      let attributes += [ attribute ]
    endif
  endfor

  if !empty(attributes)
    exe 'hi ' . hl.name . ' cterm=' . join(attributes, ',')
  endif
endfunction


" {>1} Top-level control

" {>2} Variable storing highlights between runs
" This allows us to remember what the highlights looked like when we last ran,
" and compare against it the next time we're called.  Using this means that we
" can avoid work when we'd just be duplicating our own work if we tried to
" match the gui colors to cterm colors again.  More subtly, it also allows us
" to support composite colorschemes that start with a :colorscheme to load an
" existing colorscheme, and then add or modify highlights that the sourced
" scheme provides.  Since we get called twice by such a scheme, things would
" fall apart without info saved between runs - the first call would set some
" high colors, and the second would bail because some high colors are set; it
" would think that the scheme was already 256 color even though it wasn't.
let s:highlights = {}

" {>2} Builtin cterm color names above 15
" Vim defines some color name to high color mappings internally (see
" syntax.c:do_highlight).  Since we don't want to overwrite a colorscheme that
" was actually written for a high color terminal with our choices, but have no
" way to tell if a colorscheme was written for a high color terminal, we fall
" back on guessing.  If any highlight group has a cterm color set to 16 or
" higher, and it wasn't set by this script, we assume that the user has used
" a high color colorscheme - unless that color is one of the below, which vim
" can set internally when a color is requested by name.
let s:presets_88  = []
let s:presets_88 += [32] " Brown
let s:presets_88 += [72] " DarkYellow
let s:presets_88 += [84] " Gray
let s:presets_88 += [84] " Grey
let s:presets_88 += [82] " DarkGray
let s:presets_88 += [82] " DarkGrey
let s:presets_88 += [43] " LightBlue
let s:presets_88 += [61] " LightGreen
let s:presets_88 += [63] " LightCyan
let s:presets_88 += [74] " LightRed
let s:presets_88 += [75] " LightMagenta
let s:presets_88 += [78] " LightYellow

let s:presets_256  = []
let s:presets_256 += [130] " Brown
let s:presets_256 += [130] " DarkYellow
let s:presets_256 += [248] " Gray
let s:presets_256 += [248] " Grey
let s:presets_256 += [242] " DarkGray
let s:presets_256 += [242] " DarkGrey
let s:presets_256 += [ 81] " LightBlue
let s:presets_256 += [121] " LightGreen
let s:presets_256 += [159] " LightCyan
let s:presets_256 += [224] " LightRed
let s:presets_256 += [225] " LightMagenta
let s:presets_256 += [229] " LightYellow

" {>2} Highlight comparator
" Comparator that sorts numbers matching the highlight id of the 'Normal'
" group before anything else; all others stay in random order.  This allows us
" to ensure that the Normal group is the first group we set.  If it weren't,
" we could get E419 or E420 if a later color used guibg=bg or the likes.
function! s:SortNormalFirst(num1, num2)
  if a:num1 == hlID('Normal') && a:num1 != a:num2
    return -1
  elseif a:num2 == hlID('Normal') && a:num1 != a:num2
    return 1
  else
    return 0
  endif
endfunction

" {>2} Main function
" Wrapper around the actual implementation to make it easier to ensure that
" all temporary settings are restored by the time we return, whether or not
" something was thrown.  Additionally, sets the 'verbose' option to the max of
" g:CSApprox_verbose_level (default 1) and &verbose for the duration of the
" main function.  This allows us to default to a message whenever any error,
" even a recoverable one, occurs, meaning the user quickly finds out when
" something's wrong, but makes it very easy for the user to make us silent.
function! s:CSApprox()
  try
    let savelz  = &lz

    set lz

    " colors_name must be unset and reset, or vim will helpfully reload the
    " colorscheme when we set the background for the Normal group.
    " See the help entries ':hi-normal-cterm' and 'g:colors_name'
    if exists("g:colors_name")
      let colors_name = g:colors_name
      unlet g:colors_name
    endif

    " Similarly, the global variable "syntax_cmd" must be set to something vim
    " doesn't recognize, lest vim helpfully switch all colors back to the
    " default whenever the Normal group is changed (in syncolor.vim)...
    if exists("g:syntax_cmd")
      let syntax_cmd = g:syntax_cmd
    endif
    let g:syntax_cmd = "PLEASE DON'T CHANGE ANY COLORS!!!"

    " Set up our verbosity level, if needed.
    " Default to 1, so the user can know if something's wrong.
    if !exists("g:CSApprox_verbose_level")
      let g:CSApprox_verbose_level = 1
    endif

    " Set 'verbose' set to the maximum of &verbose and CSApprox_verbose_level
    exe max([&vbs, g:CSApprox_verbose_level]) 'verbose call s:CSApproxImpl()'
  finally
    if exists("colors_name")
      let g:colors_name = colors_name
    endif

    unlet g:syntax_cmd
    if exists("syntax_cmd")
      let g:syntax_cmd = syntax_cmd
    endif

    let &lz   = savelz
  endtry
endfunction

" {>2} CSApprox implementation
" Verifies that the user has not started the gui, and that vim recognizes his
" terminal as having enough colors for us to go on, then gathers the existing
" highlights, removes the ones that match what were set on the last run
" through, and sets the cterm colors to match the gui colors for all modified
" highlights.
function! s:CSApproxImpl()
  " Return if not running in an 88/256 color terminal
  if has('gui_running') || (&t_Co != 256 && &t_Co != 88)
    if &verbose && !has('gui_running') && &t_Co != 256 && &t_Co != 88
      echomsg "CSApprox skipped; terminal only has" &t_Co "colors, not 88/256"
      echomsg "Try checking :help csapprox-terminal for workarounds"
    endif

    return
  endif

  " Get the current highlight colors
  let highlights = s:Highlights()

  " If the Normal group is cleared, set it to gvim's default, black on white
  " Though this would be a really weird thing for a scheme to do... *shrug*
  if highlights[hlID('Normal')].gui.bg == ''
    let highlights[hlID('Normal')].gui.bg = 'white'
  endif

  if highlights[hlID('Normal')].gui.fg == ''
    let highlights[hlID('Normal')].gui.fg = 'black'
  endif

  " Create a list of colors that have changed since the last iteration
  let modified = []
  for hlid in keys(highlights)
    if    !has_key(s:highlights, hlid)
     \ || s:highlights[hlid].cterm != highlights[hlid].cterm
     \ || s:highlights[hlid].gui   != highlights[hlid].gui
      let modified += [hlid]
    endif
  endfor

  " Make sure that the script is not already 256 color by checking to make
  " sure that no modified groups are set to a value above 256, unless the
  " color they're set to can be set internally by vim (gotten by scraping
  " color_numbers_{88,256} in syntax.c:do_highlight)
  for hlid in modified
    let val = highlights[hlid]
    if   (    val.cterm.bg > 15
         \ && index(s:presets_{&t_Co}, str2nr(val.cterm.bg)) < 0
         \ && val.cterm.bg !=
            \   get(get(get(s:highlights, hlid, {}), 'cterm', {}), 'bg', ''))
    \ || (    val.cterm.fg > 15
         \ && index(s:presets_{&t_Co}, str2nr(val.cterm.fg)) < 0
         \ && val.cterm.fg !=
            \   get(get(get(s:highlights, hlid, {}), 'cterm', {}), 'fg', ''))
      " The value is set above 15, and wasn't set by us or vim.
      if &verbose >= 2
        echomsg 'CSApprox: Exiting - high color found for' val.name
      endif
      return
    endif
  endfor

  " We need to set the Normal group first so 'bg' and 'fg' work as colors
  call sort(modified, "s:SortNormalFirst")

  " then set each modified color's cterm attributes to match gui
  for hlid in modified
    call s:SetCtermFromGui(highlights[hlid])
  endfor

  " and finally, store the new highlights for use in the next iteration
  let s:highlights = highlights
endfunction

" {>1} Hooks

" {>2} Autocmds
" Set up an autogroup to hook us on the completion of any :colorscheme command
augroup CSApprox
  au!
  au ColorScheme * call s:CSApprox()
augroup END

" {>2} Execute
" The last thing to do when sourced is to run and actually fix up the colors.
call s:CSApprox()

" {>1} Restore compatibility options
let &cpo = s:savecpo
unlet s:savecpo


" {0} vim:sw=2:sts=2:et:fdm=expr:fde=substitute(matchstr(getline(v\:lnum),'^\\s*"\\s*{\\zs.\\{-}\\ze}'),'^$','=','')