src_dst 1 1
   src_blend 0
   mode set
   menger_sponge 2

src_dst 1 2
   src_blend 1
   menger_sponge 3

# now we have a menger sponge with inner gradient

# make some noise and map a part of it to 0
src_dst 0 0
   fill_noise 3 P2.1,2.9 0.2
   map_range 0 0.4  0 0

# now we draw only a portion of the menger sponge
# depending on the 0s in the noise
src_dst 0 2
   src_blend 1
   src_range 0 0
   fill

# make some more noise:
src_dst 1 1
   fill_noise 3 2 0.5 1
   map_range 0 1 0.05 0.5

# now we draw some noise over the inner cores:
src_dst 1 2
   src_range 0 1
   dst_range 0.05 0.5
   fill

   #show_range_sector_type A2 3