Bug 489548

Created attachment 171240 [details]
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.