SUMMARY Reposting from https://krita-artists.org/t/how-is-the-copy-blending-mode-practically-different-from-normal/10799 , artifacts start appearing on the canvas in some cases when using Copy paint layers and/or when using a brush preset set to Copy. This does not seem to happen with Filter layers. When Copy is applied to the brush preset, it does not seem to happen when using the Color Smudge, Hatching, Deform, or Filter brush engines. To reproduce using layers: 1. Have a white background layer and an empty layer 1 2. Set layer 1 to Copy 3. Draw, observe transparency artifacting 4. Move layer 1 around a bit, observe more artifacting 5. Set layer 1 back to Normal Observed result: Lots of artifacting leftover, can be wiped away by changing opacity of background layer To reproduce using a brush preset: 1. Have a white background layer and an empty layer 1 2, Set a Pixel engine brush to Copy 3. Draw two different circles overlapping each other, observe (intentional?) blocking of white around stroke area 4. Change opacity of background layer Observed result: The blocking in step 3 gets thickened for some reason EXPECTED RESULT I'm not totally sure how Copy works so I'm not totally sure what to expect, but at the very least it shouldn't leave leftover artifacts when switching a Copy layer back to Normal, SOFTWARE/OS VERSIONS Linux/KDE Plasma: Debian sid (available in About System) KDE Plasma Version: 5.17.5 KDE Frameworks Version: 5.70.0 Qt Version: 5.12.8 (Appimage) ADDITIONAL INFORMATION This happens regardless if it's the CPU canvas or the OpenGL canvas. The artifacting might become more apparent when spamming undo after these steps.
I can confirm this for the Aug13 4.3.1 alpha (git adcd40a) appimage and it happens for the 4.2.0 appimage onwards. The situation and the various effects that can be observed are many, varied and complicated. It has to be seen to be fully appreciated. For a layer set to Copy blending mode, if you paint on it with any brush engine, there are artifacts around the brush stroke. If you then toggle the Background layer, it won't come back to visible. If you then turn off the paint layer, you get a white rectangle that is larger than the bounding box of the painted stroke. If you then set the layer blending mode to normal, you get the painted stroke on the white rectangle. Then toggling the Background layer brings it back to visible. Then setting the layer blending mode to Copy gives a different set of behaviours as you toggle the visibility of the two layers in different ways. For a brush preset painting in Copy mode, there are artifacts around the stroke for the Pixel engine brushes and other brush engines but not the Colour Smudge, unless it is used close to the stroke from another brush engine, in which case there are hidden artifacts that are revealed by painting with the Colour Smudge brush preset. For a Filter layer, there are no artifacts when switching from Normal layer blending to Copy Blending. Panting on a filter layer with a brush preset set to Copy mode does give artifacts around the stroke. If the filter layer is then set to Copy blending mode, these artifacts become larger.
I'm not sure if bug reporters can edit the importance of their filed bugs, but if I could, I would bump this up to normal importance since it's pretty strange for a feature to be so visibly glitchy.
Yes, this should be marked normal, not minor.
Copy layers might have been fixed as a part of the fix to https://bugs.kde.org/show_bug.cgi?id=439729 (from what I perceive), however brushes with Copy blending mode are still visually buggy.