newline

Adding text support to zone-nyan was relatively simple after figuring out a suitable representation. To render the data, I iterate over a two-dimensional array, look up the current cell in the color mapping, then insert an appropriate representation of it. It was tempting to use (newline) after each line, but that works differently from the seemingly more bothersome (insert "\n"). A look at the sources reveals why:

(defun newline (&optional arg interactive)
  "Insert a newline, and move to left margin of the new line if it's blank.
If option `use-hard-newlines' is non-nil, the newline is marked with the
text-property `hard'.
With ARG, insert that many newlines.

If `electric-indent-mode' is enabled, this indents the final new line
that it adds, and reindents the preceding line.  To just insert
a newline, use \\[electric-indent-just-newline].

Calls `auto-fill-function' if the current column number is greater
than the value of `fill-column' and ARG is nil.
A non-nil INTERACTIVE argument means to run the `post-self-insert-hook'."
  (interactive "*P\np")
  (barf-if-buffer-read-only)
  ;; Call self-insert so that auto-fill, abbrev expansion etc. happens.
  ;; Set last-command-event to tell self-insert what to insert.
  (let* ((was-page-start (and (bolp) (looking-at page-delimiter)))
         (beforepos (point))
         (last-command-event ?\n)
         ;; Don't auto-fill if we have a numeric argument.
         (auto-fill-function (if arg nil auto-fill-function))
         (postproc
          ;; Do the rest in post-self-insert-hook, because we want to do it
          ;; *before* other functions on that hook.
          (lambda ()
            (cl-assert (eq ?\n (char-before)))
            ;; Mark the newline(s) `hard'.
            (if use-hard-newlines
                (set-hard-newline-properties
                 (- (point) (prefix-numeric-value arg)) (point)))
            ;; If the newline leaves the previous line blank, and we
            ;; have a left margin, delete that from the blank line.
            (save-excursion
              (goto-char beforepos)
              (beginning-of-line)
              (and (looking-at "[ \t]$")
                   (> (current-left-margin) 0)
                   (delete-region (point)
                                  (line-end-position))))
            ;; Indent the line after the newline, except in one case:
            ;; when we added the newline at the beginning of a line which
            ;; starts a page.
            (or was-page-start
                (move-to-left-margin nil t)))))
    (unwind-protect
        (if (not interactive)
        ;; FIXME: For non-interactive uses, many calls actually just want
        ;; (insert "\n"), so maybe we should do just that, so as to avoid
        ;; the risk of filling or running abbrevs unexpectedly.
        (let ((post-self-insert-hook (list postproc)))
          (self-insert-command (prefix-numeric-value arg)))
      (unwind-protect
          (progn
            (add-hook 'post-self-insert-hook postproc nil t)
            (self-insert-command (prefix-numeric-value arg)))
        ;; We first used let-binding to protect the hook, but that was naive
        ;; since add-hook affects the symbol-default value of the variable,
        ;; whereas the let-binding might only protect the buffer-local value.
        (remove-hook 'post-self-insert-hook postproc t)))
      (cl-assert (not (member postproc post-self-insert-hook)))
      (cl-assert (not (member postproc (default-value 'post-self-insert-hook))))))
  nil)

Even assuming that the FIXME gets dealt with, you should resist the urge and use (insert "\n") for programmatically added newlines.