Bug 406400

Summary:	Black artifacts when painting with brush on 32-bit image with Vector Optimizations enabled
Product:	[Applications] krita	Reporter:	Dmitry Kazakov <dimula73>
Component:	Brush engines	Assignee:	Krita Bugs <krita-bugs-null>
Status:	RESOLVED DUPLICATE
Severity:	normal	CC:	ghevan, tamtamy.tymona
Priority:	NOR	Keywords:	release_blocker
Version:	git master (please specify the git hash!)
Target Milestone:	---
Platform:	Other
OS:	All
Latest Commit:		Version Fixed In:
Attachments:	Screenshot of the problem Rendering error on 32bit float

Description Dmitry Kazakov 2019-04-10 09:46:23 UTC

Created attachment 119329 [details]
Screenshot of the problem

1) Enable Vector Optimizations (VC) in the performance tab
2) Create a 32-bit float image
3) Draw with Basic-5 Size brush

Observe random black tiles aligned by 32/16-byte level (8/4 pixels).

See the attached screenshot.

The bug appears on both Windows and Linux with Vc 1.3.3, with either AVX or SSE4 implementation used. It means that it is unrelated to bug 406209. It is somehow related to our implementation of AlphaDarkenCompositor128 and OverCompositor128.


PS:
Or a bug in Vc...

PPS:
Or a bug in GCC...

Comment 1 vanyossi 2019-04-10 16:42:58 UTC

Created attachment 119337 [details]
Rendering error on 32bit float

The behaviour is a little different on macOS compiled sources.

Vc 1.4.1
Clang Apple LLVM version 10.0.1 (clang-1001.0.46.3)

Comment 2 Tiar 2019-04-20 09:34:56 UTC

On Windows 10 and on Linux Mint with Qt 5.11 the artifacts are red, too. They seem to be multiplied with the stroke. To see the artifacts, instead of making the stroke, put one stamp on the canvas.

*** This bug has been marked as a duplicate of bug 404133 ***