Created attachment 125670 [details]
Halftone filter problem stages

SUMMARY
This is seen with the 4.2.0 and onwards appimages and the Feb 03 4.3.0 prealpha appimage git 8e38e39
It does not happen with the krita 4.1.7 appimage.

If an object is painted on a transparent paint layer and then the Halftone filter is applied, there are minor artifacts around the edges of the resulting image and then major artifacts which are revealed after layer visibility is toggled.

The attached image, halftone-bugs.png, shows sub-images a,b,c,d which illustrate this.

STEPS TO REPRODUCE
1. Draw an object such as shown in a) on a transparent paint layer.
2. Apply Filter -> Artistic - Halftone and wait for the on-screen image to be processed.
3. Note that the result is as shown in b) with local artifacts around the edges.
4. Note that the layers docker thumbnail for the layer shows major artifacts as in c).
5. Toggle the layer visibility.
6. Note that the major artifacts are now part of the layer as shown in d) and seem to correspond to the right and lower edges of a content bounding box.

OBSERVED RESULT
This happens if the anti-aliasing option of the halftone filter is on or off.
It happens if graphics acceleration and/or instant preview are on or off.

It does not happen if the object is on a solid colour layer.

EXPECTED RESULT
No artifacts

SOFTWARE/OS VERSIONS
Krita

 Version: 4.3.0-prealpha (git 8e38e39)
 Languages: en_GB, en, en, en_GB, en
 Hidpi: true

Qt

  Version (compiled): 5.12.5
  Version (loaded): 5.12.5

OS Information

  Build ABI: x86_64-little_endian-lp64
  Build CPU: x86_64
  CPU: x86_64
  Kernel Type: linux
  Kernel Version: 4.19.0-6-amd64
  Pretty Productname: Debian GNU/Linux 10 (buster)
  Product Type: debian
  Product Version: 10

OpenGL Info
 
  Vendor:  "NVIDIA Corporation" 
  Renderer:  "GeForce GTX 750 Ti/PCIe/SSE2" 
  Version:  "4.6.0 NVIDIA 418.74" 
  Shading language:  "4.60 NVIDIA" 
  Requested format:  QSurfaceFormat(version 3.0, options QFlags<QSurfaceFormat::FormatOption>(DeprecatedFunctions), depthBufferSize 24, redBufferSize 8, greenBufferSize 8, blueBufferSize 8, alphaBufferSize 8, stencilBufferSize 8, samples -1, swapBehavior QSurfaceFormat::DoubleBuffer, swapInterval 0, colorSpace QSurfaceFormat::DefaultColorSpace, profile  QSurfaceFormat::CompatibilityProfile) 
  Current format:    QSurfaceFormat(version 4.6, options QFlags<QSurfaceFormat::FormatOption>(DeprecatedFunctions), depthBufferSize 24, redBufferSize 8, greenBufferSize 8, blueBufferSize 8, alphaBufferSize 8, stencilBufferSize 8, samples -1, swapBehavior QSurfaceFormat::DoubleBuffer, swapInterval 0, colorSpace QSurfaceFormat::DefaultColorSpace, profile  QSurfaceFormat::CompatibilityProfile) 
     Version: 4.6
     Supports deprecated functions true 
     is OpenGL ES: false 

QPA OpenGL Detection Info 
  supportsDesktopGL: true 
  supportsOpenGLES: true 
  isQtPreferOpenGLES: false 

Hardware Information

  GPU Acceleration: auto
  Memory: 16039 Mb
  Number of Cores: 8
  Swap Location: /tmp

Current Settings

  Current Swap Location: /tmp
  Undo Enabled: 1
  Undo Stack Limit: 18
  Use OpenGL: 1
  Use OpenGL Texture Buffer: 1
  Use AMD Vectorization Workaround: 0
  Canvas State: OPENGL_SUCCESS
  Autosave Interval: 360
  Use Backup Files: 1
  Number of Backups Kept: 1
  Backup File Suffix: ~
  Backup Location: Same Folder as the File
  Use Win8 Pointer Input: 0
  Use RightMiddleTabletButton Workaround: 0
  Levels of Detail Enabled: 1
  Use Zip64: 0

Display Information
Number of screens: 2
	Screen: 0
		Name: DVI-D-1
		Depth: 24
		Scale: 1
		Resolution in pixels: 1280x1024
		Manufacturer: Dell Inc.
		Model: DELL 1704FPV-
		Refresh Rate: 60
	Screen: 1
		Name: DVI-D-0
		Depth: 24
		Scale: 1
		Resolution in pixels: 1280x1024
		Manufacturer: Dell Inc.
		Model: DELL 1704FPV-
		Refresh Rate: 75