[digikam] [Bug 373839] New: Continuously face thumbnails flicker/update

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https://bugs.kde.org/show_bug.cgi?id=373839

            Bug ID: 373839
           Summary: Continuously face thumbnails flicker/update
           Product: digikam
           Version: unspecified
          Platform: Other
                OS: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: NOR
         Component: Thumbnails
          Assignee: [hidden email]
          Reporter: [hidden email]
  Target Milestone: ---

When opening the people view in a large window allowing for many faces, the
thumbnails will flicker continuously.

Steps to reproduce
==================
1) Use the faces images from http://cswww.essex.ac.uk/mv/allfaces/faces94.html
   http://cswww.essex.ac.uk/mv/allfaces/faces94.zip
2) Create test folder and put the images there.
3) Create a new test database, and use the images above
5) Open the People view, and scan all images for faces using the default
options.
5) Look for Unknown, and set the size of the face thumbnails to smallest
(124px)
6) Make the window size for Digikam large enough until the flicker starts. I
usually get it with > ~210 faces (thumbnails).

Expected result
================
People view displays the thumbnails without flicker.

Actual result
===============
People view displays the thumbnails constant flickering

Additional info
===============
See video of flickering at https://youtu.be/AwmapnWNDBw
I get this on my laptop and desktop.

I was using digikam built from sources
(d72b486b7109fd80f6071fd78af2b9509de56044)

Observation
===========
It seems that applying following patch makes the flicker go away. But I'm not
sure  what the downside of the patch is...

krikar@krikar-desktop:~/dev/kde/digikam/core$ git diff
diff --git a/app/items/imagecategorizedview.cpp
b/app/items/imagecategorizedview.cpp
index d5847c7..ba6dd47 100644
--- a/app/items/imagecategorizedview.cpp
+++ b/app/items/imagecategorizedview.cpp
@@ -737,14 +737,14 @@ ImageInfoList ImageCategorizedView::resolveGrouping(const
QModelIndexList indexe
 void ImageCategorizedView::paintEvent(QPaintEvent* e)
 {
     // We want the thumbnails to be loaded in order.
-    ImageThumbnailModel* const thumbModel = imageThumbnailModel();
+/*    ImageThumbnailModel* const thumbModel = imageThumbnailModel();

     if (thumbModel)
     {
         QModelIndexList indexesToThumbnail =
imageFilterModel()->mapListToSource(categorizedIndexesIn(viewport()->rect()));
         d->delegate->prepareThumbnails(thumbModel, indexesToThumbnail);
     }
-
+*/
     ItemViewCategorized::paintEvent(e);
 }

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--- Comment #1 from Kristian Karl <[hidden email]> ---
I noticed this first, when using a maximized Digikam window on a 4K monitor,
where enough faces/thumbnails were rendered to cause the flickering.

Reducing the size of the Digikam window will make the flickering go away.

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                 CC|                            |[hidden email]
            Version|unspecified                 |5.3.0

--- Comment #2 from [hidden email] ---
Can you reproduce the problem with pre-release 5.4.0 AppImage univerdal bundle
for Linux available here :

https://drive.google.com/drive/folders/0BzeiVr-byqt5Y0tIRWVWelRJenM

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--- Comment #3 from Kristian Karl <[hidden email]> ---
Yes, I could reproduce the problem on the pre-release 5.4.0 AppImage.

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            Version|5.3.0                       |5.4.0

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--- Comment #4 from Kristian Karl <[hidden email]> ---
The flickering still exists digikam 5.7.0, installed from neon CI repository:
aptitude show digikam                                                          
Package: digikam                                                                
State: installed                                                                
Automatically installed: no                                                    
Version: 4:5.5.0+p16.04+git20170621.0646-0                                      
Priority: optional                                                              
Section: graphics                                                              
Maintainer: Neon CI <[hidden email]>                                              
Architecture: amd64                                                            
Uncompressed Size: 26,6 M                                                      
Depends: digikam-data (= 4:5.5.0+p16.04+git20170621.0646-0), libqt5sql5-sqlite,
perl, libc6 (>= 2.14),        
         libexiv2-14 (>= 0.25), libexpat1 (>= 2.0.1), libgcc1 (>= 1:3.0),
libgl1-mesa-glx | libgl1, libgomp1  
         (>= 4.9), libgphoto2-6 (>= 2.5.9), libgphoto2-port12 (>= 2.5.9),
libjasper1, libjpeg8 (>= 8c),      
         libkf5akonadicontact5, libkf5calendarcore5, libkf5configcore5,
libkf5configgui5,                    
         libkf5configwidgets5, libkf5contacts5, libkf5coreaddons5,
libkf5filemetadata3, libkf5i18n5,          
         libkf5iconthemes5, libkf5kdelibs4support5, libkf5kiowidgets5,
libkf5kipi32.0.0, libkf5notifications5,
         libkf5notifyconfig5, libkf5sane5, libkf5service5, libkf5solid5,
libkf5threadweaver5,                
         libkf5widgetsaddons5, libkf5windowsystem5, libkf5xmlgui5, liblcms2-2
(>= 2.2+git20110628),          
         liblensfun0 (>= 0.2.8), liblqr-1-0 (>= 0.4.0), libmarblewidget-qt5-28,
libopencv-contrib2.4v5,      
         libopencv-core2.4v5, libopencv-imgproc2.4v5, libopencv-objdetect2.4v5,
libpng12-0 (>= 1.2.13-4),    
         libqt5concurrent5 (>= 5.9.0), libqt5core5a (>= 5.9.0), libqt5dbus5 (>=
5.9.0), libqt5gui5 (>= 5.9.0),
         libqt5network5 (>= 5.9.0), libqt5opengl5 (>= 5.9.0),
libqt5printsupport5 (>= 5.9.0), libqt5sql5 (>=  
         5.9.0), libqt5webkit5, libqt5widgets5 (>= 5.9.0), libqt5x11extras5,
libqt5xml5 (>= 5.9.0), libstdc++6
         (>= 5.2), libtiff5 (>= 4.0.3), libx11-6

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--- Comment #5 from [hidden email] ---
Here, i tried with digiKam 5.7.0 + Qt 5.9. + KF5 5.35, and OpenCV 3.1.0 with a
4K monitor under Mageia6. I cannot reproduce the problem.

Which screen resolution do you use exactly ?

Gilles Caulier

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--- Comment #6 from Kristian Karl <[hidden email]> ---
I have seen this problem on 2 different 4K screens. One connected to my
midtower machine.
And last, my laptop Lenovo Thinkpad X240 connected using Display Port to a BenQ
BL3201PT 32-inch Ultra HD, running 3840x2160 30 FPS

It does not matter what size I have on the thumbnails, 128 or 256 px.

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