01  function rgb_hsl( rgb_ )
02    dim h
03    dim s
04    dim l
05  
06    dim r: r = rgb_( COLOR_R ) / NUMBER_MAX_BYTE
07    dim g: g = rgb_( COLOR_G ) / NUMBER_MAX_BYTE
08    dim b: b = rgb_( COLOR_B ) / NUMBER_MAX_BYTE
09  
10    dim min: min = number_mini( number_mini( r, g ), b )
11    dim max: max = number_maxi( number_maxi( r, g ), b )
12  
13    dim delta: delta = max - min
14    dim sigma: sigma = max + min
15    dim kappa: kappa = sigma / 2.0
16  
17    l = sigma / 2.0
18  
19    if( delta = 0.0 ) then
20      h = 0.0
21      s = 0.0
22    else
23      if( l < 0.5 ) then
24        s = delta / sigma
25      else
26        s = delta / ( 2.0 - sigma )
27      end if
28  
29      if( r = max ) then
30        h = ( g - b ) / delta
31      else
32        if( g = max ) then
33          h = ( b - r ) / delta + 2.0
34        else
35          h = ( r - g ) / delta + 4.0
36        end if
37      end if
38  
39      h = h / 6.0
40  
41      if( h < 0.0 ) then h = h + 1.0
42      if( h > 1.0 ) then h = h - 1.0
43    end if
44    rgb_hsl = array( h, s, l )
45  end function