Beta #4 - Thumbnail problem in browser mode with png files (HQ webp caching)

[masterjp]

I used the browser viewer in XnvIewMP 1.0 Beta #3 and scroll through my directory with jpg und png files.
There are some new files at the end of the window, which I wanted to see.
Some png files show a wrong thumbnail preview, because I scrolled the right slider to the bottom.

Here is a preview:



If I refresh the thumbnails with the function the view menu, everything looks correct.

[xnview]

do you have same problem in previous version?

[masterjp]

The problem exists since XnViewMP 1.00 beta #1. I tried every beta version to get closer to the reason of the problem.
XnViewMP 0.99.7 works fine! The Plugin folder files do not produce the error

I tried different scenarios:

1. XnViewMP 0.99.7 works fine! No problems.

2. XnViewMP 1.00 beta #4 with ZIP or JPEG compression for thumbnail cache WORKS FINE!!!

3. I copied all files and folders from the 'plugin' folder from XnViewMP 1.00 beta #4 to the older version 0.99.7.
No problems with thumbnails!

4. I copied the plugin folder from version 0.99.7 to XnViewMP 1.00 beta #1, 2, 3 and 4. => Problem exists!
I get the problem with different png files (32 bit true color pictures - maybe an alpha channel problem?!?)
24 bit color pictures look fine!

I will only see the wrong thumbnails of special png files, if I create the thumbnails with the XnViewMP 1.00 beta version.
At the first time I start the browser viewer window, all thumbnails are displayed correctly.
If I close XnViewMP and open the same folder in browser mode again,
I will see the wrong black and white line thumbnails from my screenshot.

So something in the viewing or loading sourcecode for thumbnails have been changed.
I use the thumbnail caching mode with WEBP quality.
Here is a sample file for testing.

[xnview]

ok, i can reproduce. WebP library remove alpha channel when empty

[masterjp]

Great