Let me try to explain if this doesn't make sense...

When you add a filter layer in Krita, if you happen to have an active selection then the filter will ONLY apply to the area of the selection. It is as if the filter layer is created with a transparency mask attached. However there is no transparency mask, at least not one I can see in the layers list.

So once this is done I can't find any way to change what area the filter applies to. So far I've been making a new filter layer then manually copying numbers over to the new one, then deleting the old one. Also, I've just been avoiding using them because of this.

So is there a way to edit this "hidden transparency mask"? (Even if there is, this behavoir seems pretty confusing. My suggested feature request would be to make a proper transparency mask in this case...)

Thanks for any help!

- K

version: krita-4.2.7-beta1-x86_64.appimage

The 'easy' answer would be to use a suitable group structure and put a filter mask on the group layer. Filter masks do have a mask that you can paint on, as you know.
When you make a selection and then add a filter layer, the filter effect only applies to the selected region but you can use the Move tool to move that region around after deselection. You can also transform that region, scale, rotate, etc. This suggests a bounding box around the filter layer 'content' and not a mask type of control method. Think of it as invisible 'filter paint'. You could try using the Transform tool to adjust the shape/extent of such a region.

You can use drawing and erasing on the filter layer to edit it. So, just press backspace(fill with background color) to completely fill the filterlayer area, or use del to clear it completely.