Bad performance in gallery view

[amymor]

Describe the bug
When you open a folder with a lot of images and want to show the gallery, the app tries to load the entire folder, which uses a lot of resources.

Expected behavior
It should be something like Explorer that only shows cached thumbnails, so the program should also use Windows thumbnails instead of loading the entire folder into memory.

Screenshots

[Ruben2776]

Some updates to this issue: The image gallery has been the most difficult thing to get right. I do feel the performance and stability for it has been lacking, but it is not because of a lack of trying.

Expected behavior
It should be something like Explorer that only shows cached thumbnails, so the program should also use Windows thumbnails instead of loading the entire folder into memory.

I think you want it to use Windows thumbnails for performance reasons? When PicView was a WPF application, it did use the old Windows API code pack though I was unable to carry that over to Avalonia. Now it uses Magick.NET and Avalonia for thumbnail generation. Getting thumbnails from Windows is a thing I want back though, and would love some help there.

The thumbs are actually loaded much faster than what is shown in the UI, however. That is because I need to call the Dispatcher with a Background priority in order to not make the UI laggy and unresponsive. Essentially, that means the thumbs are loaded very fast and then gradually added to the UI. That is the real issue/bottleneck that needs addressing.

I am using a WrapPanel for the container, which is required to expand the gallery, and then downsize it again into the docked status, as well for the item and line spacing logic. Currently, Avalonia does not have a VirtualizingWrapPanel which I believe could solve this issue. However, there is the VIrtualingWrappenel PR here AvaloniaUI/Avalonia.Labs#92 as well as the VirtualizingStackPanel: AvaloniaUI/Avalonia#20993 which might help this issue.