Issue Summary

Manipulating the imported frames will cause visual artefacts to the alpha channel transformed by the move tool in the area surrounded by the rectangular marquee causing a "black fill" (usual color representation for transparency / alpha values).

I've already tested this with all the other import options and only the movie video options does this.

There are three components that seem to be related to this:

1. The movie video import feature. It could be an FFMPEG incorrectly configurated flag or a specific problem with the exact format conversion.
2. The selection & move tools. Transforming the image is the only way to bring this issue forth.
3. Image cache. After doing some experiments I've also seen that the image cache for the produced artifact can be affected via deleting the "fill"

Note: it's also unexpected that I can undo the "glitch" all the time.

Expected Results

Having no visual glitch nor incorrect alpha channel information for any imported image either bitmap or vector.

Video or Image Reference

https://youtu.be/HAaUtoLCfLU

Steps to reproduce

1. Import a movie video
2. Create a selection that covers part of the image and part of the transparent canvas (the bg color of the canvas doesn't matter)
3. use the move tool to transform the image
4. Notice the transparent part became filled with black.

System Information

• Pencil2D Version:

Nightly Build May 11 2021

commit: 7ba6e71
date: 2021-05-11_07:39:53

Operating System: Windows 10 Version 2009
CPU Architecture: x86_64
Qt Version: 5.15.2