function [out] = rendsegment (spec)
%rendsegment 

out = [0; 0];
numcomps = length (spec);
for i = 1:numcomps,
  opseg = spec{i};
  opstart = opseg{1};
  disp ((sprintf ('rendering %d', i)));
  tmpout = rceval (opseg{2});
  tmplen = length (tmpout);
  opend = opstart + tmplen - 1;
  [dummy, outlen] = size (out);
  if (opend > outlen)
    out = [out, (zeros (2, (opend - outlen + 1)))];
  end
  out(:,(opstart+1):(opend+1)) = out(:,(opstart+1):(opend+1)) + tmpout;
end

return;