Unexpected behavior with MouseMultiCursor on empty columns

[Atemo-C]

Using MouseMultiCursor, the cursors are added/removed properly. However, it also activates when moving the mouse horizontally on an empty column.

For example, if I move my mouse ever so slightly horizontally on the ruler bar or at the end of a line, I do not want it to spam select/unselect i. It makes for a very poor multi-cursor selection experience.

2025-03-26.16-08-28.mp4

[dmaluka]

However, it also activates when moving the mouse horizontally on an empty column.

You mean, when moving mouse with the mouse button pressed?

Which version of micro are you using? In v2.0.14 the behavior of MouseMultiCursor was significantly changed: now it is only activated when pressing the mouse, not when moving with the mouse already pressed (see #2606), plus it now allows to unset an already set multicursor by clicking on it once again (see #3146).

[Atemo-C]

You mean, when moving mouse with the mouse button pressed?

Yes, with Ctrl too.

Which version of micro are you using?

2.0.14, as per https://search.nixos.org/packages?channel=unstable&show=micro

In my configuration, I have this as a binding:
"Ctrl-MouseLeftDrag": "MouseMultiCursor".

[dmaluka]

In my configuration, I have this as a binding:
"Ctrl-MouseLeftDrag": "MouseMultiCursor".

Ok, this explains it. This is intended behavior (since #3146): MouseMultiCursor not just adds a multicursor but toggles it, i.e. removes a multicursor if it as already there. So when you drag mouse to a line which already has a multicursor at the end, this multicursor is removed.

I didn't expect there would be any users that actually prefer the pre-#2606 behavior (adding multicursor not just on mouse press but also on mouse drag) and even bind Ctrl-MouseLeftDrag to MouseMultiCursor to bring this old behavior back. I thought this behavior was very annoying (it was so easy to accidentally add an unwanted cursor by moving the mouse, and before #3146 it wasn't even possible to remove this accidentally added cursor without removing all cursors).

...Ok, sorry, after reading your description of the issue once again, I see what you are complaining about is not that MouseMultiCursor removes a cursor if it's already there, but that it it does that also on an empty column. That is also an intended behavior. It is similar, for example, to simply clicking (without Ctrl) on a position to move the cursor there (the standard MousePress action): it is useful to be able to put the cursor at the end of a line without "aiming" exactly at the character at the end of this line, just by clicking somewhere to the right of it.

To work around this to address your use case, you can bind Ctrl-MouseLeftDrag to a lua function which calls MouseMultiCursor only if the mouse position is on an actual character within a line, like this:

function mouseMultiCursorExact(bp, e)
    local mx, my = e:Position()
    local bview = bp:BufView()
    if my < bview.Y or my >= bview.Y + bview.Height then
        return false
    end
    if mx < bview.X then
        return false
    end
    local loc = bp:LocFromVisual(buffer.Loc(mx, my))
    local vloc = bp:VLocFromLoc(loc)
    if mx ~= bview.X + vloc.VisualX then
        return false
    end

    return bp:MouseMultiCursor(e)
end

[Atemo-C]

you can bind Ctrl-MouseLeftDrag to a lua function which calls MouseMultiCursor only if the mouse position is on an actual character within a line

Huh, I did not even know one could bind to a Lua function. That being said, I have no idea how to actually do it, as in; Where do I put the function, and how do I invoke it in bindings.json?

[dmaluka]

Put it in ~/.config/micro/init.lua. Also before the function add this line:

local buffer = import("micro/buffer")

(since the function uses buffer.Loc)

Then bind Ctrl-MouseLeftDrag to lua:initlua.mouseMultiCursorExact in your bindings.json.

It is described in the tutorial: https://github.com/zyedidia/micro/blob/master/runtime/help/tutorial.md#configuration-with-lua

[Atemo-C]

Thank you. I followed your steps, but this seems to make it impossible to select multiple items in a single click when on an empty column, I have to click every single line individually — which is the opposite of what I want.

2025-03-27.00-36-52.mp4

[dmaluka]

I thought you said if was a problem for you that "it also activates when moving the mouse horizontally on an empty column."

Ok, I think now I get it: you don't want it to activate when moving horizontally, but you do want it to activate when moving vertically. So, you want something very tailored.

Well, that can be programmed in Lua too. Something like this?

local buffer = import("micro/buffer")

local lastMulticursorLoc = buffer.Loc(-1, -1)

function mouseMultiCursorNoHorizontal(bp, e)
    local mx, my = e:Position()
    local loc = bp:LocFromVisual(buffer.Loc(mx, my))
    if loc == lastMulticursorLoc then
        return false
    end

    lastMulticursorLoc = loc
    return bp:MouseMultiCursor(e)
end

[dmaluka]

[...] Something like this?

Actually this is probably not fully correct (though might be good enough for you). We should probably also reset lastMulticursorLoc back to buffer.Loc(-1, -1) when releasing the mouse, and so on.

[Atemo-C]

[…] Something like this?

This actually works exactly how I want it to! May I close this issue as solved?

[dmaluka]

May I close this issue as solved?

Sure.