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Re: Pixel scrolling support

From: Po Lu
Subject: Re: Pixel scrolling support
Date: Fri, 26 Nov 2021 17:29:25 +0800
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/28.0.60 (gnu/linux)

Eli Zaretskii <eliz@gnu.org> writes:

> pixel-scroll-precision-mode sounds better to me.

Hmm, I don't think that's quite right, but I can't explain how it's not.
I think it would be best to keep it as `pixel-scroll-precise-mode'.

>> -** New minor mode 'better-pixel-scroll-mode'.
>> +** New minor mode 'pixel-scroll-precise-mode'.
>>  When enabled, using this mode with a capable scroll wheel will result
>>  in the display being scrolled precisely according to the turning of
>>  that wheel.

> This text doesn't really describe what the mode does.  It basically
> says something like "pixel-scroll-precise-mode scrolls precisely".
> the main part that was left unexplained is "according to the turning of
> that wheel", and specifically the "according" part.

How about this: "When enabled, you can scroll the display up or down by
individual pixels in a way that corresponds with the movement of your
mouse wheel, if supported by the mouse wheel."?

> What is the problem with scrolling by more than the window's height?

Basically, we use `posn-at-x-y' to find the window start and the vscroll
that's wanted, which doesn't work when y is outside the window.

> I think you should detect the EOB condition early on and simply not
> scroll at all in that case.

I couldn't find a way to know if scrolling will result in EOB before it
actually happens.

>> +(defun pixel-scroll-precise (event &optional arg)
>> +  "Scroll the display according to EVENT.

> This sentence should include something to indicate the "precise"
> feature.  Otherwise it is too general, indistinguishable from any
> other scroll command.

Hmm, how about "Scroll the display by pixels according to EVENT"?

>> +Take into account any pixel deltas in EVENT to scroll the display
>> +according to the user's turning the mouse wheel.  If EVENT does
>> +not have precise scrolling deltas, call `mwheel-scroll' instead.

> This describes what the code does, not what the user should expect in
> terms of the effect on the screen.

  "Scroll the display vertically by pixels according to EVENT.
Move the display up or down by the pixel deltas in EVENT to
scroll the display according to the user's turning the mouse

How's this instead?

>> +ARG is passed to `mwheel-scroll', should that be called."

> Likewise: the description of ARG should be similar to how we describe
> the effect of prefix arg in other similar commands.

Actually, this command doesn't handle hscroll, so ARG seems to be
pointless.  Removed, thanks.

> Shouldn't this say something about "setting the variable doesn't have
> any effect"?

Yes, my bad.

> And what about horizontal scrolling?

It doesn't handle horizontal scrolling, so I changed the doc strings to
specify that the display is scrolled vertically by these commands.


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