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I'd like to find all occurrences of == in a buffer and overlay them with Unicode ≡, keeping width of two chars and centered in the space.

I know about replacing text visual representation:

(put-text-property 1 10 'display "replacement")

about keeping known width

(put-text-property 1 10 'display '(space :width (119)))

I do not know how to put this together and keep it centered.

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  • I don't have an answer to your question, but one option would be to create a custom XPM image that is the width of two characters and center that image when designing it. You can have a function that calculates and adds/removes pixels / columns as needed based upon the frame character width, and frame character height.
    – lawlist
    Commented Mar 14, 2015 at 3:33

1 Answer 1

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While my solution doesn't really center, it comes close enough I hope. There is a display property that adjusts the width of all spaces, if I use the string ≡ and make its spaces half the width, it will look centered and two characters wide. The only downside I could find so far is that putting the cursor on the propertized string highlights its first space.

Here's a demonstration that should produce two lines of code lining up perfectly upon evaluating it with C-x C-e and point after the end of the expression:

(insert "\na == b\n"
        "a " (propertize "=" 'display
                         (propertize " ≡ " 'display '(space-width 0.5)))
        " b\n")
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  • By judicious use of the cursor text-property, you should be able to make Emacs draw the cursor over the ≡ sign instead of drawing it over the preceding space.
    – Stefan
    Commented Mar 14, 2015 at 13:25
  • @Stefan I doubt it's worth it though.
    – wasamasa
    Commented Mar 14, 2015 at 15:24

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