; ono-rgb.lsp  11june2009 dmemos
 
( set 'cmax 255 'cmin 0 )
( set 'cdelta ( / ( - cmax cmin) 10 )) 
( set 'drgb ( dup cdelta 3 ))
( set 'white ( dup cmax 3 ))
( set 'black ( dup cmin 3 ))
( set 'red ( list cmax cmin cmin ))
( set 'green ( list cmin cmax cmin ))
( set 'blue ( list cmin cmin cmax ))

( define ( limit rgbx)
  ( if ( > rgbx cmax) cmax 
   ( if ( < rgbx cmin) cmin rgbx )))

( define ( rgb-add rgb1 rgb2 )
( map limit ( map + rgb1 rgb2)))

( define ( rgb-sub rgb1 rgb2 )
( map limit ( map - rgb1 rgb2)))

( define ( rgb-complement rgb1 )
( rgb-sub white rgb1 ))

( set 'yellow ( rgb-add red green ))
( set 'cyan ( rgb-add green blue ))
( set 'magenta ( rgb-add red blue ))

( define ( rgb-lighter rgb1 i )
( if ( = nil i ) (set 'i 1 ))
( rgb-add rgb1 ( map * drgb ( list i i i ))))

( define ( rgb-darker rgb1 i )
( if ( = nil i ) (set 'i 1 ))
( rgb-sub rgb1 ( map * drgb ( list i i i ))))

( set 'darkgrey ( rgb-lighter black 3 ))
( set 'lightgrey ( rgb-darker white ))