Created attachment 126920 [details]
Screencap of issue

When more than 1 fish-eye rulers are on the canvas, parts of the canvas will turn black and stop rendering (or be blocked by something rendering in front of it) at certain zoom levels. This effect is more prominent the more the rulers overlap, and the larger they are.
Everything works as intended behind the 'black screen', other than the drawing will no longer be visible until either you zoom out, or delete the second ruler.





System info:
Krita
  Version: 4.3.0-prealpha (git 44d8e02)

Qt
  Version (compiled): 5.12.7
  Version (loaded): 5.12.7

OS Information
  Build ABI: x86_64-little_endian-llp64
  Build CPU: x86_64
  CPU: x86_64
  Kernel Type: winnt
  Kernel Version: 10.0.17134
  Pretty Productname: Windows 10 (10.0)
  Product Type: windows
  Product Version: 10


OpenGL Info
 
  Vendor:  "Google Inc." 
  Renderer:  "ANGLE (NVIDIA GeForce GTX 980 Ti Direct3D11 vs_5_0 ps_5_0)" 
  Version:  "OpenGL ES 3.0 (ANGLE 2.1.0.57ea533f79a7)" 
  Shading language:  "OpenGL ES GLSL ES 3.00 (ANGLE 2.1.0.57ea533f79a7)" 
  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 3.0, options QFlags<QSurfaceFormat::FormatOption>(), depthBufferSize 24, redBufferSize 8, greenBufferSize 8, blueBufferSize 8, alphaBufferSize 8, stencilBufferSize 8, samples 0, swapBehavior QSurfaceFormat::DefaultSwapBehavior, swapInterval 0, colorSpace QSurfaceFormat::DefaultColorSpace, profile  QSurfaceFormat::NoProfile) 
     Version: 3.0
     Supports deprecated functions false 
     is OpenGL ES: true 

QPA OpenGL Detection Info 
  supportsDesktopGL: true 
  supportsAngleD3D11: true 
  isQtPreferAngle: false 

Hardware Information
 Memory: 63 Gb
 Cores: 12
 Swap: C:/Windows/Temp