[Bug 178540] New: zoom in previewwidget has poor behaviour

http://bugs.kde.org/show_bug.cgi?id=178540

           Summary: zoom in previewwidget has poor behaviour
           Product: digikam
           Version: unspecified
          Platform: Compiled Sources
        OS/Version: MS Windows
            Status: UNCONFIRMED
          Severity: normal
          Priority: NOR
         Component: general
        AssignedTo: [hidden email]
        ReportedBy: [hidden email]


Version:            (using KDE 4.1.3)
Compiler:          N/A N/A
OS:                MS Windows
Installed from:    Compiled From Sources

source file: graphics/digikam/libs/widgets/common/previewwidget.cpp

previewwidget is used in a few places, imagepreviewview.cpp being one.

The zoom in out functionality has a few undesired behaviours.

Some to do with the use of:

QFrame::contentsRect().width()/.height()
instead of
QScrollView::visibleHeight()/visibleWidth()

or

conflicts between centering the image in extra vertical/horz. space and
centering the contents scrolling within the viewport

also accounting for the appearance/disappearance of the scroll bars changing
the visible area.

(Note: I have a patch that fixes all of these things, I just have to learn how
to get it approved.)


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Gilles Caulier caulier gilles gmail com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|general                     |Preview
            Version|unspecified                 |0.10.0-svn




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--- Comment #1 from Gilles Caulier <caulier gilles gmail com>  2008-12-23 22:14:10 ---
brandon,

just attach the patch to this bugzilla file. That all... We will review
later...

Gilles Caulier


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--- Comment #2 from brandon <brandon sharpideas ca>  2008-12-24 02:00:27 ---
Created an attachment (id=29594)
 --> (http://bugs.kde.org/attachment.cgi?id=29594)
Patch to improve scroll zooming.

Here is the code I am playing around with so far. It will be less verbose after
I test it a little more.

Basically to re-state the problem:

You should be able to put the mouse over a point on an image and use the scroll
wheel to zoom all the way to max zoom right to that point without having to
move the mouse.

As previewwidget.cpp works now you have to keep re-centering the mouse on the
point you are trying to zoom in on.

This is because there are limitations to Q3ScrollView. It can't for example
scroll negatively or, scroll so far that the right edge of an image is in the
center of the viewport.

To overcome this you need to either 'bump' the mouse cursor, to keep it
centered on the zoomCenterPoint, or adjust the pixmap x/y co-ordinates.

Right now I am only, 'bumping' the cursor, so you can smoothly zoom right in to
any point on the image even the edges without having to reposition the mouse.

In the future it might be worth adjusting the pixmap location as well,
especially for the right and bottom edges. However the problem with adjusting
the pixmap location is, it is once it has been adjusted it's impossible to know
when the user would want the image be re-centered.

Anyway hope somebody likes using scroll-zoom and finds this useful.

I'm new to Qt/Kde so don't be shy about pointing out things I could have done
better.


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brandon brandon sharpideas ca changed:

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--- Comment #3 from brandon <brandon sharpideas ca>  2008-12-24 02:02:32 ---
I forgot to mention, this patch was created from the
<svn-workspace>/graphics/digikam directory.

Is this the correct location to create patches from?


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--- Comment #4 from Gilles Caulier <caulier gilles gmail com>  2008-12-24 13:08:17 ---
<svn-workspace>/graphics/digikam directory sound fine... if you use trunk not
branches :

http://websvn.kde.org/trunk/extragear/graphics/digikam/

Gilles Caulier


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--- Comment #5 from Marcel Wiesweg <marcel wiesweg gmx de>  2008-12-29 22:46:28 ---
Brandon, I think we are positive about applying your patch, if you have it well
tested and give us a version that you call final we will commit it.

(There is a comment in your code calling for configurability of the Ctrl
modifier.  I think this was chosen due to being KDE standard, and we cannot
endlessly add options)


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--- Comment #6 from Gilles Caulier <caulier gilles gmail com>  2009-01-01 14:30:00 ---
Andi,

Are you tested this patch ?

Gilles


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--- Comment #7 from Andi Clemens <andi clemens gmx net>  2009-01-01 14:37:47 ---
Not now, I will test it soon, just fixing something with the menu entries in
digiKam. After that I will do it.

Andi


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--- Comment #8 from Andi Clemens <andi clemens gmx net>  2009-01-01 15:27:03 ---
The patch seems to work quite well, but sometimes the point I'm focusing is not
centered when zooming in, although it should be possible to center the image.
When I select a point I want to zoom to, it can happen that this point moves
out of the visible area.
In general I would say the patch is fine, maybe Q3ScrollView is not capable of
doing it better?

Andi


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--- Comment #9 from Marcel Wiesweg <marcel wiesweg gmx de>  2009-01-08 22:59:39 ---
Well I'm afraid but I have to say that the current implementation works much
better for me than with the patch applied.
With the patch there is a tendency of the cursor to move top-left. E.g. if I
start in the bottom-right corner and zoom in and out ten or fifteen times, the
cursor finally ends up in the top-left corner. This does not happen with the
current implementation. Maybe there's a difference between Linux and Windows?

Apart from this, I get these compilation warnings:
/home/marcel/freshmeat/multimedia/kde4/src/extragear/graphics/digikam/libs/widgets/common/previewwidget.cpp:
In member function ‘void Digikam::PreviewWidget::setZoomFactor(double,
bool)’:                                                                      
/home/marcel/freshmeat/multimedia/kde4/src/extragear/graphics/digikam/libs/widgets/common/previewwidget.cpp:252:
warning: unused variable ‘oldZoom’  
/home/marcel/freshmeat/multimedia/kde4/src/extragear/graphics/digikam/libs/widgets/common/previewwidget.cpp:
In member function ‘virtual void
Digikam::PreviewWidget::contentsWheelEvent(QWheelEvent*)’:                    
/home/marcel/freshmeat/multimedia/kde4/src/extragear/graphics/digikam/libs/widgets/common/previewwidget.cpp:680:
warning: comparison between signed and unsigned integer expressions            
/home/marcel/freshmeat/multimedia/kde4/src/extragear/graphics/digikam/libs/widgets/common/previewwidget.cpp:
In member function ‘void Digikam::PreviewWidget::setZoomFactor(double,
bool)’:                                                                      
/home/marcel/freshmeat/multimedia/kde4/src/extragear/graphics/digikam/libs/widgets/common/previewwidget.cpp:253:
warning: ‘cpy’ may be used uninitialized in this function                  
/home/marcel/freshmeat/multimedia/kde4/src/extragear/graphics/digikam/libs/widgets/common/previewwidget.cpp:253:
warning: ‘cpx’ may be used uninitial


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--- Comment #10 from Gilles Caulier <caulier gilles gmail com>  2009-07-22 15:15:28 ---
Well, closed as won't fix ???

Gilles Caulier

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           What    |Removed                     |Added
----------------------------------------------------------------------------
            Version|0.10.0-svn                  |0.10.0




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--- Comment #11 from Andi Clemens <andi clemens gmx net>  2009-10-08 01:37:07 ---
Push.... :)

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           What    |Removed                     |Added
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             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |WONTFIX




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           Platform|Compiled Sources            |MS Windows

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