From a524f51da9e67c1f7048b00ab934b8061251341b Mon Sep 17 00:00:00 2001
From: Tim Vaughan <tgvaughan@gmail.com>
Date: Sun, 19 May 2019 22:24:07 +0200
Subject: [PATCH] Initial string processing function seems to work.

---
 sixel.el | 39 +++++++++++++++++++++------------------
 1 file changed, 21 insertions(+), 18 deletions(-)

diff --git a/sixel.el b/sixel.el
index 958a456..2539356 100644
--- a/sixel.el
+++ b/sixel.el
@@ -31,17 +31,18 @@
         (aset sixel i tag))
     (setq n (/ n 2))))
 
-(defun sixel-tag-sixel-in-row (row-variable index char tag)
+(defun sixel-tag-sixel-in-row (row index char tag)
   "Tag the bits of the sixel at INDEX in the list identified by
 the variable ROW-VARIABLE corresponding to input character CHAR
 with TAG."
-  (while (not (< index (length (symbol-value row-variable))))
-    (add-to-list row-variable (make-vector 6 nil)))
-  (let ((sixel (elt (symbol-value row-variable) index)))
-    (sixel-tag-bits sixel (- char 63) tag)))
+  (while (not (< index (length row)))
+    (push (make-vector 6 nil) row))
+  (let ((sixel (elt row (- (length row) 1 index))))
+    (sixel-tag-bits sixel (- char 63) tag))
+  row)
 
 (defun sixel-process-data (string)
-  "Convert sixel string into a list of lists representing individual sixels."
+  "Convert STRING into a list of lists representing individual sixels."
   (with-temp-buffer
     (insert string)
     (goto-char (point-min))
@@ -63,28 +64,30 @@ with TAG."
           (let ((tag (intern (match-string 1))))
             (setq current-colour tag)))
 
-         ((looking-at "$")
+         ((looking-at "\\$")
           (setq idx-out 0))
 
-         ((looking-at "^-")
-          (push this-row 'rows)
+         ((looking-at "-")
+          (push (reverse this-row) rows)
           (setq this-row nil)
           (setq idx-out 0))
 
-         ((looking-at "^!\\([0-9]+\\)\\([?-~]\\)")
+         ((looking-at "!\\([0-9]+\\)\\([?-~]\\)")
           (let ((repeat-count (string-to-number (match-string 1)))
                 (char (elt (match-string 2) 0)))
             (dotimes (i repeat-count)
-              (sixel-tag-sixel-in-row 'result idx-out char current-colour))))
+              (setq this-row
+                    (sixel-tag-sixel-in-row this-row idx-out char current-colour))
+              (setq idx-out (1+ idx-out)))))
 
-         ((looking-at "^\\([?-~]\\)")
+         ((looking-at "\\([?-~]\\)")
           (let ((char (elt (match-string 1) 0)))
-            (sixel-tag-sixel-in-row 'result idx-out char current-colour)))
+            (setq this-row
+                  (sixel-tag-sixel-in-row this-row idx-out char current-colour))
+            (setq idx-out (1+ idx-out))))
 
-         ((= (point) (point-max))
-          (setq finished t))
-
-         (t (error "Invalid characters found in input string.")))
+         (t (setq finished t)))
 
         (goto-char (match-end 0)))
-      (push this-row 'rows))))
+      (push (reverse this-row) rows)
+      (reverse rows))))
-- 
2.20.1