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

[Kristian Karl]

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: digikam-devel at kde.org
          Reporter: kristian.hermann.karl at gmail.com
  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 at 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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