SUMMARY
This happens with the Apr-13 5.0.0 prealpha git bf6f43c appimage
It does not happen with the Apr-13 4.3.0 'Plus' git ae2e6e5 appimage

The Advanced Colour Selector has a very slow response to dragging the hue around the outer ring and also a very slow response to dragging the selected colour around inside the SV triangle.

If you quickly click-drag around a circular path, within the triangle, and then relase the click, the selected colour will spend five seconds following the path of that drag.

The selected colour sample square updates in a 'stuttered' manner while this is happening.

The Specific Colour Selector has a small amount of lag with slider darg that is not bad but is noticeable compared the the 4.3.0 'Plus' version.

STEPS TO REPRODUCE
See Sumamry

OBSERVED RESULT
See Sumamry

EXPECTED RESULT
It should be very fast to follow the cursor.

SOFTWARE/OS VERSIONS
Krita

 Version: 5.0.0-prealpha (git bf6f43c)
 Languages: en_GB, en, en, en_GB, en
 Hidpi: true

Qt

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

OS Information

  Build ABI: x86_64-little_endian-lp64
  Build CPU: x86_64
  CPU: x86_64
  Kernel Type: linux
  Kernel Version: 4.19.0-8-amd64
  Pretty Productname: Debian GNU/Linux 10 (buster)
  Product Type: debian
  Product Version: 10
  Desktop: MATE

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
  Current Swap Location writable: true
  Undo Enabled: true
  Undo Stack Limit: 18
  Use OpenGL: true
  Use OpenGL Texture Buffer: true
  Use AMD Vectorization Workaround: false
  Canvas State: OPENGL_SUCCESS
  Autosave Interval: 60
  Use Backup Files: true
  Number of Backups Kept: 1
  Backup File Suffix: ~
  Backup Location: Same Folder as the File
  Backup Location writable: false
  Use Win8 Pointer Input: false
  Use RightMiddleTabletButton Workaround: false
  Levels of Detail Enabled: false
  Use Zip64: false


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