.PS
#   dpicopt = 7; optPS=8; optPDF=5; optMFpic=7; optSVG=11; optMpost = 10;
    r = 0; g = 0; b = 0.6

B: box invis ht 8 wid 7.5 with .sw at 0,0
if 1 then {
  move to B.nw+(0.5,-1.4)
for i = 1 to 2 do {
  linethick = 0.8
  for s = 0.0625 to 1.01 by *2 do {
    b = min(s,1)
#                           Could copy dpictools.pic and use DefineRGBColor:
    if (dpicopt==optPS) || (dpicopt==optPDF) then {
       define customcolor {sprintf("%g %g %g",r,g,b)}
       } \
    else {if dpicopt==optMFpic then {
       command sprintf("\mfpdefinecolor{color_}{rgb}{%g,%g,%g}",r,g,b)
       define customcolor {"color_"} } \
    else {if dpicopt==optSVG then {
       define customcolor {sprintf("rgb(%g,%g,%g)",\
         int(r*255),int(g*255),int(b*255))} }\
    else {if dpicopt==optMpost then {
       define customcolor {sprintf("(%g,%g,%g)",r,g,b) } }\
    else {
       command sprintf("\definecolor{color_}{rgb}{%g,%g,%g}",r,g,b)
       define customcolor {"color_"} }}}}

    if s > 0.0625 then {move right s}
    arc cw rad s from Here+(0,-s) to Here+(s,0) \
      with .c at Here <-> wid s*1.2 ht s*1.2 color customcolor
    linethick = linethick*2
    if s < 1 then { move right s } 
    } # for s 
  move to B.nw+(0.5,-4)
  arrowhead = 0
  } # for i
} # if

  arrowhead = 0
  linethick = 4
  r = 0.5
  s = 1
if 1 then {
  move to B.nw+(1,-6.0)
 {for i=1 to 4 do {
    if i > 1 then {move right s}
    arc cw rad r from Here+(0,-r) to Here+(r,0) \
      with .c at Here <-> wid .5 ht .5
    if i < 4 then {linethick = linethick*1.5}
  }}
}
if 0 then {
  move down 1.5; right
  {for i=2 to 4 do {
    move right s
    arc cw rad r from Here+(0,-r) to Here+(r,0) \
      with .c at Here <-> wid .5*i ht 1
  }}
}
    
  linethick = 0.8
# box wid B.wid ht B.ht at B
if 1 then {
  move to B.ne+(-1,-1)
  arc cw rad 0.5 from Here+(.25,-.25) to Here+(.25,.25) <-> 1
  { line <- 1 up left from last arc.end+(0.1,0.1) }

  [A: arc cw rad 0.5 from Here+(.25,-.25) to Here+(.25,.25) <-> 0
   { line <- 0 up left from last arc.end+(0.1,0.1) }
   ] with .A.c at last arc.c+(0,-2.5)
  }
.PE
