3

Emacs displays characters without glyphs as octal escape sequences "\OOO", e.g., from the start of a PDF file:

%PDF-1.4
%\344\343\317\322
1 0 obj
[/PDF/ImageB/ImageC/ImageI/Text]
endobj
4 0 obj
<</Length 5 0 R/Filter/FlateDecode>>
stream
9\323\317\221\321\356j\305
endstream

Can I set some (relatively simple) configuration to get those in hexadecimal escape sequences "\xFF"? As:

%PDF-1.4
%\xE4\xE3\xCF\xD2
1 0 obj
[/PDF/ImageB/ImageC/ImageI/Text]
endobj
4 0 obj
<</Length 5 0 R/Filter/FlateDecode>>
stream
9\xD3\xCF\x91\xD1\xEEj\xC5
endstream

(using text-mode, or fundamental-mode, or... but not hexl-mode)

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1 Answer 1

Reset to default
2

I've never played with this before, but reading the Elisp manual a bit and experimenting makes me think that something like this is what you're looking for:

(let ((ii          128)
      (new-dtable  (make-display-table))
      (hex-string  nil))
  (while (< ii 256) ; Convert decimal codes 128 to 255.
    (setq hex-string  (format "%X" ii))
    (aset new-dtable ii
          (vector
           (make-glyph-code ?\ 'escape-glyph)
           (make-glyph-code ?x 'escape-glyph)
           (make-glyph-code (aref hex-string 0) 'escape-glyph)
           (make-glyph-code (aref hex-string 1) 'escape-glyph)))
    (setq ii  (1+ ii)))
  (set-window-display-table (selected-window) new-dtable))

If you then use, say C-q 3 4 4 RET, which normally inserts the octal escape sequence \344, it will insert a glyph showing xE4.

The relevant part of the Elisp manual I looked at are those under node Character Display.

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5
  • Looks good, yet it does not work completely. I have no time now to investigate deeper, but it seems it is converting newly inserted characters, but not the pre-existant ones
    – Rolazaro Azeveires
    Dec 14, 2013 at 10:15
  • That sounds it has to do with the way the redisplay and the display table work. I'm no expert on that. You might need to force redisplay (e.g. force-mode-line-update with ALL arg) or even revisit the buffer (e.g. C-x v or revert). (You are welcome to upvote or accept the answer, BTW. ;-) )
    – Drew
    Dec 14, 2013 at 16:28
  • Upvoted because it is useful, not accepted (yet?) because it does not (yet) solve it. And I hate being asked to vote
    – Rolazaro Azeveires
    Dec 14, 2013 at 19:20
  • FYI - For me it does also convert pre-existing chars in the buffer. Did you try adding a call to force-mode-line-update (with non-nil arg)? For me the code works with both Emacs 24 (recent dev snapshot) and Emacs 23.4, on MS Windows.
    – Drew
    Dec 15, 2013 at 0:23
  • Try also iconifying (minimizing) and then restoring the frame, or just resizing the frame. Try also killing the buffer and re-creating it (at least to see whether that helps).
    – Drew
    Jan 12, 2016 at 16:01

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