PS
# brace.m4
gen_init
NeedDpicTools

divert(-1)
                              `bracket(linespec, end depth,
                                 thickness, end thickness, attributes)
                               Square bracket along linespec
                               default depth is linewid/5
                               attributes = eg
                                 thick 0.4 outlined "string" shaded "string"
                                 (default black)'
define(`bracket',`rpoint_(ifelse(`$1',,`to rvec_(linewid,0)',`$1'))
M4brS: last line.start; M4brE: last line.end
[ brdepth = ifelse(`$2',,linewid/5,`($2)')
  brthick = ifelse(`$3',,brdepth/6,`($3)')
  endthick = ifelse(`$4',,brthick/3,`($4)')
  define(`m4brackattribs',
   `ifelse(`$5',,`thick 0.4 shaded rgbstring(0,0,0)',`$5')')dnl
  {line m4brackattribs \
    from M4brS+vec_(0,brdepth) to M4brS+vec_(0,brdepth+brthick) \
    then to M4brE+vec_(0,brdepth+brthick) \
    then to M4brE \
    then to M4brE+vec_(-endthick,0) \
    then to M4brE+vec_(-endthick,brdepth) \
    then to M4brS+vec_( endthick,brdepth) \
    then to M4brS+vec_( endthick,0) \
    then to M4brS \
    then to M4brS+vec_(0,brdepth) }
  S: M4brS
  ] with .S at Here')

                              `brace(linespec,depth,arm thickness,attributes)
                               Curly brace along linespec
                               default depth is linewid/5
                               attributes = eg
                                 thick 0.4 outlined "string" shaded "string"
                                 (default black)'
define(`brace',`rpoint_(ifelse(`$1',,`to rvec_(linewid,0)',`$1'))
 M4brS: last line.start; M4brE: last line.end
 [ brdepth = ifelse(`$2',,linewid/5,`$2')
   brthick = ifelse(`$3',,brdepth/6,`$3')
   define(`m4braceattribs',
    `ifelse(`$4',,`thick 0.4 shaded rgbstring(0,0,0)',`$4')')dnl
   tension = 0.55
   halfwid = distance(M4brS,M4brE)
   smallrad = brdepth-brthick
   bigrad = brdepth+brthick
   for sgn=1 to -1 by -2 do {
     S: rvec_(sgn*halfwid/2,0)
     A: S+vec_(0,smallrad/2)
     B: vec_(0,smallrad/2)
     T: vec_(0,brdepth)
     C: vec_(0,bigrad/2)
     D: vec_(sgn*halfwid/2,bigrad/2)
     {spline tension m4braceattribs \
       from S to tension between S and A \
       then to tension between A-vec_(sgn*bigrad/2,0) and A \
       then to A-vec_(sgn*bigrad/2,0) \
       then to B+vec_(sgn*bigrad/2,0) \
       then to tension between B+vec_(sgn*bigrad/2,0) and B \
       then to tension between T and B \
       then to T \
       then to tension between T and C \
       then to tension between C+vec_(sgn*bigrad/2,0) and C \
       then to C+vec_(sgn*bigrad/2,0) \
       then to D-vec_(sgn*bigrad/2,0) \
       then to tension between D-vec_(sgn*bigrad/2,0) and D \
       then to tension between S and D \
       then to S }
     }
   E: (0,0)
] with .E at 0.5 between M4brS and M4brE')
divert(0)dnl

 del = 0.2
 maxht = 2
 minht = 0.3
 n = 16
 hmax = 360
R1: [
 for i=0 to n-1 do {
   x = i/n
   y = minht*(1-x)+maxht*x
   hsvtorgb(x*hmax,1,1,r,g,b)
   brace(from (    -i*del,-y/2)  up y,,,thick 0.4 shaded rgbstring(r,g,b))
   brace(from ((i+1)*del, y/2) down y,,,thick 0.4 \
     outlined rgbstring(r,g,b) shaded rgbstring(r,g,b))
   }
 ]
R2: [
 for i=0 to n-1 do {
   x = i/n
   y = minht*(1-x)+maxht*x
   hsvtorgb(x*hmax,1,1,r,g,b)
   brace(from (    -i*del,-y/2)  up y,5bp__+x*20bp__,2bp__+x*13bp__,thick 0.4 \
     shaded rgbstring(r,g,b))
   brace(from ((i+1)*del, y/2) down y,5bp__+x*20bp__,2bp__+x*13bp__,thick 0.4 \
     outlined rgbstring(r,g,b) shaded rgbstring(r,g,b))
   }
 ] with .n at R1.s+(0,-0.2)
R3: [
 for i=0 to n-1 do {
   x = i/n
   y = minht*(1-x)+maxht*x
   hsvtorgb(x*hmax,1,1,r,g,b)
   bracket(from (   -i*del,-y/2)   up y, 5bp__+x*20bp__, 2bp__+x*13bp__,,
     thick 0.4 shaded rgbstring(r,g,b))
   bracket(from ((i+1)*del, y/2) down y, 5bp__+x*20bp__, 2bp__+x*13bp__,,
     thick 0.4 outlined rgbstring(r,g,b) shaded rgbstring(r,g,b))
   }
 ] with .n at R2.s+(0,-0.2)

PE