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#25592
Feature request: sorting overlays
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Message #38 received at 25592 <at> debbugs.gnu.org (full text, mbox):
> Cc: 25592 <at> debbugs.gnu.org
> From: Clément Pit--Claudel <clement.pitclaudel <at> live.com>
> Date: Sun, 5 Feb 2017 11:21:04 -0500
>
> > Why would you need to keep track of overlays, if you always process
> > each one just once?
>
> To avoid applying the same overlay twice. But I think I understand your suggestion better now, and you meant that I would apply each overlay's properties not to the entire overlay's range (overlay-start .. overlay-end), but instead just to the current range (as determined by next-overlay-change). Correct?
Yes, of course. That's how the display engine handles overlays.
> > But the "simpler" solution has a problem, whereby the order of the
> > overlays might depend on buffer position for which you evaluate the
> > order, because overlays could begin at the same position, but end at
> > different ones, or vice versa. IOW, the overlaps between portions
> > of the buffer text "covered" by different overlays could be partial.
> > How do you handle this situation in your algorithm? The correct
> > solution would require having different values of the corresponding
> > text property for different locations, according to the
> > highest-priority overlay at each location. Am I missing something?
>
> I think I'm probably the one missing something :) I'm not sure I understand the problem. Here's my current algorithm:
> [...]
> (defun esh--commit-overlays (buf)
> "Copy overlays of BUF into current buffer's text properties."
> (let ((pt-min-diff (- (with-current-buffer buf (point-min)) (point-min))))
> (dolist (ov (esh--buffer-overlays buf))
> (let* ((start (max (point-min) (- (overlay-start ov) pt-min-diff)))
> (end (min (point-max) (- (overlay-end ov) pt-min-diff)))
> (ov-props (overlay-properties ov))
> (cat-props (let ((symbol (plist-get ov-props 'category)))
> (and symbol (symbol-plist symbol))))
> (face (let ((mem (plist-member ov-props 'face)))
> (if mem (cadr mem) (plist-get cat-props 'face))))
> (props (esh--filter-plist (append cat-props ov-props)
> (cons 'face esh--overlay-specific-props))))
> (when face
> (font-lock-prepend-text-property start end 'face face))
> (add-text-properties start end props)))))
What will happen if you have 2 overlays like this:
+------------- OV2 -------+
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
+------- OV1 ---------+
and OV2 has a higher priority than OV1?
> >>>>> How did you implement in Lisp the "last resort" of
> >>>>> comparison, which compares addresses of the C structs?
> >>>>
> >>>> I didn't :)
> >>>
> >>> So it isn't really a solution ;-)
> >>
> >> It's not a full reimplementation, but it's enough of a solution for
> >> me :) The docs say “If SORTED is non-‘nil’, the list is in
> >> decreasing order of priority”, and that's what my implementation
> >> does.
> >
> > Then there will be use cases where your solution will give a wrong
> > value to the text property that replaces the overlays.
>
> Snap. Do you have a concrete example? I imagine this would happen if two overlays are added to the same range of text, with no explicit priority?
Or with explicitly equal priority.
This bug report was last modified 8 years and 104 days ago.
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