QGIS » QGIS Application

This is not a bug, it's a feature :) ... map canvas is recentered on mouse position when using scroll wheel. I think this has been discussed some time ago on mailing list that some users think it's good and some users think it's bad.

I guess only way to satisfy both groups is to make this customizable.

Hi wonder,

also I consider this as a but. It's rendering the
mouse wheel zoom useless (with 1 "roll" back and forth
I no longer see my map but only a white area).
For me it would be fairly intuitive if mouse-scroll
zoom in/out once keeps me where I am.

Related question: how can I disable mouse wheel zoom
to avoid that I regularly get off-map just by
accidentially touching the mouse wheel?

thanks,
markus

Hi Markus,

actually we could have 3 options in global settings for what to do on scroll wheel event:
1. zoom
1. zoom and recenter
1. nothing

And first option can be default...

Martin

The behavior is pretty standard and used by other applications. I think making it a user setting with 3 options is the best solution.

Replying to [comment:1 wonder]:

This is not a bug, it's a feature :)

You missed the point of the bug report.

map canvas is recentered on mouse position when using scroll wheel.

I'm not complaining it is doing it. I'm complaining it is not doing it properly, as the title reads. Again, to reproduce:

1. add some vector

2. mouse-scroll zoom in once

3. mouse-scroll zoom out once

4. goto 2 until you see how your map wanders to one side of the Map View

Don't move your mouse between steps 2 and 3. Note the map wanders in the Map View at each iteration, while it shoudn't.

Was I clear this time?

Maciek

Replying to [comment:5 [email protected]]:

map canvas is recentered on mouse position when using scroll wheel.

I'm not complaining it is doing it. I'm complaining it is not doing it properly, as the title reads. Again, to reproduce:

1. add some vector

2. mouse-scroll zoom in once

3. mouse-scroll zoom out once

4. goto 2 until you see how your map wanders to one side of the Map View

Don't move your mouse between steps 2 and 3. Note the map wanders in the Map View at each iteration, while it shoudn't.

Then I really don't understand what do you think. At my opinion, it's done correctly (recenter and zoom). Take in account that although mouse pointer is on the same poisition, its map coordinates change on every zoom in/out. Thus it's natural that your map moves away quicky if you have your pointer off the center of map view.

What is your expectation how should it work?

Martin

The behaviour of qgis on mouse scroll is working as intended (zoom and recenter on mouse position), but that behavour is not what everyone expects with a mouse scroll, and there appear to be 3 ways in which it could work.

With our desire to get 0.8 released as soon as possible, we are not terribly keen on adding new features to qgis until after 0.8 has been released. We are focussing on fixing things that cause crashes or are clearly not working as intended.

The suggestion has been made that the behaviour of qgis to a mouse zoom be made customisable to match the expectations of various users. This is sensible and is what I think we should do. However, it is an enhancement to qgis and as such should be marked against the 0.9 release.

The issue is about 'recenter'. Why is that needed? If I zoom in/out, the
center should remain the same. Maybe I am wrong on this...

Markus

Now I start to understand what happens: zoom and recenter on mouse position. So far the mouse position was random in my case and I got confused. So I would have to keep it precisely in the middle of the map to reach what I feel how it should work.
OK, confirmed.

But: For a human it's rather hard to estimate where the center of the map window is. So in most cases it will wander off (quickly).

Above Martin said:

actually we could have 3 options in global settings for what to do on scroll wheel event:

   1. zoom
   2. zoom and recenter
   3. nothing 

And first option can be default...

This sounds like a perfect solution for Maciek and me (and maybe others): make the first option the default (please).

thanks,
markus

Replying to [comment:6 wonder]:

Replying to [comment:5 [email protected]]:

Don't move your mouse between steps 2 and 3. Note the map wanders in the Map View at each
iteration, while it shoudn't.

Then I really don't understand what do you think. At my opinion, it's done correctly (recenter and zoom).

That's right. And I don't mind it.

Take in account that although mouse pointer is on the same poisition, its map coordinates change on every zoom in/out.

I don't agree. What I'm doing is zooming in and back, once, without moving my mouse. Given this, why should the map coordinates under the mouse cursor change?

Thus it's natural that your map moves away quicky if you have your pointer off the center of map view.

But I'm not moving my mouse pointer at all...

P.S.

A note regarding Markus's wish about changing the tool not to recenter, or letting the user choose his prefered behavior: that's a feature request, and although related, a separate issue. Please don't discuss it here, as it hampers the discussion clarity. Thanks.

Maciek wrote:

A note regarding Markus's wish about changing the tool not to recenter, or
letting the user choose his prefered behavior: that's a feature request,
and although related, a separate issue. Please don't discuss it here, as
it hampers the discussion clarity. Thanks.

... I disagree. If you keep the mouse in the middle of the map, it works
as expected by you (and me). So it's not a separate issue but exactly explaining
your problem (so also mine).

Anyway, I think it's clear now. I'll stop contributing to this discussion
since there is nothing else to say from my part. Will just watch what happens.

Best,
Markus

Replying to [comment:11 [email protected]]:

... I disagree. If you keep the mouse in the middle of the map, it works
as expected by you (and me). So it's not a separate issue but exactly explaining
your problem (so also mine).

Markus is correct. The reason of the fuss is that I assumed, in error, that the mouse pointer is centered in the display too, when the map is centered after a mouse-scroll zoom.

My wrong assumption came from the fact that I intuitevely moved the pointer to the map center myself, when I wanted to zoom out back. But, "For a human it's rather hard to estimate where the center of the map window is" (as Markus wrote on 12/02/06 21:26:10).

Of course I was not able to aim at the map center precisely, so I thought there was a bug, that the map is drifting because the mouse pointer is not centered properly for me (anybody still following; me hardly). Why I failed to notice that it is me trying to move the mouse pointer to the center I don't know.

Now, hoping that I know how the mouse scroll zoom works actually: could my assumption be implemented? So that when the map is centered after a mouse-scroll zoom, the mouse pointer moves along with the map, thus it is placed in the display center, but relative to the map - it remains at the same location. This would prevent the map from drifting further on at each subsequent mouse-scroll zoom.

I agree with Martin and Garry that it would be best to make this configurable, but I also agree with g_j_m that such a modification would be too intrusive for 0.8, and should be left for 0.9. But I guess that my suggestion wouldn't trigger a big modification, yet would improve usability. What do others think?

Best,
Maciek

In general, moving the mouse pointer independently of the user is 'bad' in user interface terms. The mouse pointer belongs to the user and they expect to have full control over it. Having the mouse cursor jump around when zooming would be quite confusing to me (more so than having the map drift when zooming :)

Gavin

OK then. Re-assing the bug as you wish. Thanks.

Maciek

Martin,

Thanks a lot! I will try it out soon (too late today; you don't want me to "discover" another bug half sleeping, do you? ;) ).

Cheers,

Maciek

Martin,

another happy user! I compiled it and enjoy again the mouse wheel scrolling.
Thanks so much :)

Markus

Milestone Version 0.8 deleted