bug#22873: Can we support multiple Cursors?

[Keith David Bershatsky]

I see this feature request as having two (2) distinct, yet related components.  
The fake cursors being the first component that will operate similar to 
overlays, and are thus fairly innocuous as they won't have any real affect on 
where point is located after redisplay finishes.  The second component, 
however, is the functionality that can be found in Magnar Sveen's library and 
also is present in a popular commercial editor known as Sublime Text.

I enjoy using the multiple cursors library written by Magnar Sveen, but often 
find myself taking advantage of the wait times to pour myself a cup of coffee 
while making edits with a few hundred fake cursors in a large buffer.  E.g., I 
will type the word I want inserted or tap the arrow key a few times in a 
particular direction and then walk away from the computer or surf the web while 
Emacs does its thing.  I often have to use `M-x replace-string` when dealing 
with large numbers of edits instead of using my preferred choice of multiple 
cursors.  Admittedly, I am using a slightly older customized version of Mr. 
Sveen's library -- but I don't think the basic functionality has changed all 
that much since I first started using it.

I am not a programmer by trade, but I assume there could be some significant 
speed increases by having multiple cursor abilities baked into the C code base 
of the Emacs internals.

I don't think (based on my limited programming knowledge) that all of the 
cursor-types are presently available as overlays.  I need the left bar cursor 
so that I can draw my solid vertical line that tracks the cursor position, and 
so that is what motivated me to write a sample draft patch to the C internals.  
My draft is progressing nicely, but it is slow to perfect because I am learning 
a few of the basics to the C language as I go.  I'll post to #22873 a revised 
draft of the first component (i.e., just fake cursors) in the next few days 
depending upon how many road blocks I encounter.  I've set up a simple cache of 
x/y/hpos/vpos so that recalculation is not necessary when the list of fake 
cursors doesn't change -- cursors are redrawn more than once per command loop 
depending upon what happens, e.g., with the mouse, etc.  And a user may not 
wish to change the positions of fake cursors every command loop, so the cache 
is helpful.

It may be a very long time, however, before I have enough basic skills to be 
able to implement some of the functionality of the second component.  I 
understand the implementation of feature 22873 is only a discussion at this 
point in time.  The beauty of Emacs, however, is that it's open source and I 
can make modifications to a custom build for my in-house use.  :)

Keith

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At Thu, 03 Mar 2016 07:54:17 +0100,
Marcin Borkowski wrote:
> 
> 
> * * *
> 
> What would be the added value of having that built-in vs. having it on
> M?elpa?
> 
> Best,
> 
> -- 
> Marcin Borkowski