https://bugs.kde.org/show_bug.cgi?id=489548
Bug ID: 489548
Summary: Large Blur Filter LAYER (not mask) on Blurs Alpha
Transparency Incorrectly (Sharp Boundaries / Tiles)
Classification: Applications
Product: krita
Version: 5.2.2
Platform: Microsoft Windows
OS: Microsoft Windows
Status: REPORTED
Severity: normal
Priority: NOR
Component: Filter Layers
Assignee: krita-bugs-n...@kde.org
Reporter: leod...@outlook.com
Target Milestone: ---
Created attachment 171240
--> https://bugs.kde.org/attachment.cgi?id=171240&action=edit
Comparison of filter mask and filter layer effect on a circle.
SUMMARY
Using a large blur filter LAYER doesn't produce the same results as a mask or a
destructive filter when there are fully transparent pixels on the edges of the
target.
STEPS TO REPRODUCE
1: Create a 1024x1024px document, RGB/Alpha, 8-bit.
2: Hide the white background layer, so the background becomes transparent.
3: Create a new paint layer, and draw a small circle in the middle of it.
4: Create a new filter layer with 99x99px blur or 100x100px gaussian blur.
OBSERVED RESULT
The paint layer is blurred, but there are "edges" where the blur abruptly
stops. Liked because the rendering is segmented into tiles, and the tile
boundary wasn't sufficiently expanded in this case.
In some cases, the filter is applied correctly because it fits within the
boundaries. If it appears to render correctly, try moving the paint layer
around a bit. This will create artifacts (but that's another bug, I guess).
Hiding and displaying the paint layer again gets rid of the artifacts,
refreshing the effect. Sometimes the blur will appear "clipped" at the edges.
EXPECTED RESULT
The non-destructive blur effect should be the same as if I applied the blur
directly on the paint layer.
SOFTWARE/OS VERSIONS
Windows: 11
ORIGINAL SUMMARY
This bug was originally written this way, but I managed to narrow the issue to
the problem above. I'll leave here the original bug I encountered here as well.
Using a large blur filter LAYER on a cloned layer doesn't produce the same
results as using filter mask on the cloned layer, or using the filter layer on
the original (non-clone) layer. (note: this was because when I tried it, the
original was in front of an opaque background)
ORIGINAL STEPS TO REPRODUCE
1. Create a 1024x1024px document.
2. Create a new transparent paint layer.
3. Draw a rectangle in the middle of it.
4. Create a new layer group.
5. Create a clone of the rectangle paint layer and place it into the layer
group.
6. Create a filter layer with 99x99px blur or 100x100px gaussian blur above the
paint layer.
ADDITIONAL DETAILS
I have attached the a screenshot that demonstrates the problem.
As it occurs due to transparent pixels getting automatically cropped somehow,
it's more likely to occur when you have a layer group, since the layer group's
projection will be transparent by default.
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