Desktop rendering issue with QGridLayout, Windows, Nvidia, PySide6

mliberty

I am stuck trying to troubleshoot a rendering issue where the QMainWindow background peeks through the central widget and its QGridLayout. The background should be solid black, but sometimes I see the red of the QMainWindow background like this:

The rendering issue only occurs if the QLabels are updated and the window resizes. Here is a GIF in action:

The platform is:

Windows 11 x64
Python x64 3.9.10
PySide 6.2.3 with Qt6
Renderer: NVIDIA GeForce RTX 2060/PCIe/SSE2
Version: 4.6.0 NVIDIA 511.79
Dual displays: 2194x1234+0+0 (native: 3840x2160+0+0) Available: 2194x1186+0+0

If I disable the QLabel updates using the "--noupdate" option in the script below, then this rendering issue does not occur, and the background remains solid black during window resizes.

I am posting here rather than the python group since this appears to be a Qt-related issue, not a python binding issue.

I appreciate any tips on what to investigate!

Here is the minimal example:

"""
Demonstrate PySide6 drawing artifacts
pip install -U PySide6
"""

from PySide6 import QtCore, QtGui, QtWidgets
import argparse
import sys
import time

INSTRUCTIONS = """\
Drag the bottom corner of the Window to resize it.
At some dimensions, red lines appear that remain.
The red comes from the main window's background-color
which should never peek through the central widget.
If you provide the --noupdate argument, then the
QLabels never update, and this error does not occur.
"""


TIMER_MS = 100

MAIN_WINDOW_STYLE = """\
QMainWindow {
    color: #00FF00; 
    background-color: #FF0000; 
}"""

CENTRAL_STYLE = """\
QWidget {
    padding: 0px; 
    color: #000000; 
    background-color: #000000; 
    border-width: 1px;
}"""

LABEL_STYLE = """\
QLabel {
    padding: 0px; 
    color: #FFFFFF; 
    background-color: #000000; 
    padding-left: 5px;
    padding-right: 5px;
    padding-top: 5px;
    padding-bottom: 5px; 
    border-width: 0px;
}"""


class MainWindow(QtWidgets.QMainWindow):

    def __init__(self, noupdate=False):
        super(MainWindow, self).__init__()
        self.setStyleSheet(MAIN_WINDOW_STYLE)
        self.central_widget = QtWidgets.QWidget(self)
        self.central_widget.setStyleSheet(CENTRAL_STYLE)
        self.setCentralWidget(self.central_widget)
        layout = QtWidgets.QGridLayout(self.central_widget)
        self._layout = layout
        layout.setContentsMargins(0, 0, 0, 0)
        layout.setHorizontalSpacing(0)
        layout.setVerticalSpacing(0)
        
        self._widgets = []
        widgets = self._widgets
        for row in range(4):
            for col in range(3):
                w = QtWidgets.QLabel("hi", self.central_widget)
                w.setStyleSheet(LABEL_STYLE)
                layout.addWidget(w, row * 4, col, 4, 1)
                widgets.append(w)
            for idx in range(4):
                w = QtWidgets.QLabel("hi", self.central_widget)
                w.setStyleSheet(LABEL_STYLE)
                layout.addWidget(w, row * 4 + idx, 3, 1, 1)
                widgets.append(w)
        self._timer = QtCore.QTimer()
        self._timer.setSingleShot(True)
        self._timer.timeout.connect(self._on_timer)
        if not noupdate:
            self._timer.start(TIMER_MS)
        
    @QtCore.Slot()
    def _on_timer(self):
        t = int(time.time() * 100)
        for idx, w in enumerate(self._widgets):
            w.setText(str(t + idx))
        self._timer.start(TIMER_MS)


def _parse_args():
    parser = argparse.ArgumentParser(description='Demostrate PySide6 rendering issue.')
    parser.add_argument('--noupdate', action='store_true', 
                        help='Disable QLabel updates.')
    return parser.parse_args()


if __name__ == '__main__':
    args = _parse_args()
    print(INSTRUCTIONS)
    #QtWidgets.QApplication.setAttribute(QtCore.Qt.AA_UseDesktopOpenGL)
    app = QtWidgets.QApplication()
    ui = MainWindow(noupdate=args.noupdate)
    ui.show()
    app.exec()

And here is the qtdiag output:

Qt 6.2.3 (x86_64-little_endian-llp64 shared (dynamic) release build; by MSVC 2019) on "windows" 
OS: Windows 11 Version 2009 [winnt version 10.0.22000]

Architecture: x86_64; features: SSE2 SSE3 SSSE3 SSE4.1 SSE4.2 AVX AVX2

Environment:

Features: QT_NO_EXCEPTIONS

Library info:
  PrefixPath: C:\bin\Python3_9_10\Lib\site-packages\PySide6
  DocumentationPath: C:\bin\Python3_9_10\Lib\site-packages\PySide6\doc
  HeadersPath: C:\bin\Python3_9_10\Lib\site-packages\PySide6\include
  LibrariesPath: C:\bin\Python3_9_10\Lib\site-packages\PySide6\lib
  LibraryExecutablesPath: C:\bin\Python3_9_10\Lib\site-packages\PySide6\bin
  BinariesPath: C:\bin\Python3_9_10\Lib\site-packages\PySide6\bin
  PluginsPath: C:\bin\Python3_9_10\Lib\site-packages\PySide6\plugins
  QmlImportsPath: C:\bin\Python3_9_10\Lib\site-packages\PySide6\qml
  ArchDataPath: C:\bin\Python3_9_10\Lib\site-packages\PySide6
  DataPath: C:\bin\Python3_9_10\Lib\site-packages\PySide6
  TranslationsPath: C:\bin\Python3_9_10\Lib\site-packages\PySide6\translations
  ExamplesPath: C:\bin\Python3_9_10\Lib\site-packages\PySide6\examples
  TestsPath: C:\bin\Python3_9_10\Lib\site-packages\PySide6\tests
  SettingsPath: 

Standard paths [*...* denote writable entry]:
  DesktopLocation: "Desktop" *C:\Users\Matth\Desktop*
  DocumentsLocation: "Documents" *C:\Users\Matth\Documents*
  FontsLocation: "Fonts" *C:\WINDOWS\Fonts*
  ApplicationsLocation: "Applications" *C:\Users\Matth\AppData\Roaming\Microsoft\Windows\Start Menu\Programs*
  MusicLocation: "Music" *C:\Users\Matth\Music*
  MoviesLocation: "Movies" *C:\Users\Matth\Videos*
  PicturesLocation: "Pictures" *C:\Users\Matth\Pictures*
  TempLocation: "Temporary Directory" *C:\Users\Matth\AppData\Local\Temp*
  HomeLocation: "Home" *C:\Users\Matth*
  AppLocalDataLocation: "Application Data" *C:\Users\Matth\AppData\Local\QtProject\qtdiag* C:\ProgramData\QtProject\qtdiag C:\bin\Python3_9_10\Lib\site-packages\PySide6 C:\bin\Python3_9_10\Lib\site-packages\PySide6\data C:\bin\Python3_9_10\Lib\site-packages\PySide6\data\QtProject\qtdiag
  CacheLocation: "Cache" *C:\Users\Matth\AppData\Local\QtProject\qtdiag\cache*
  GenericDataLocation: "Shared Data" *C:\Users\Matth\AppData\Local* C:\ProgramData C:\bin\Python3_9_10\Lib\site-packages\PySide6 C:\bin\Python3_9_10\Lib\site-packages\PySide6\data
  RuntimeLocation: "Runtime" *C:\Users\Matth*
  ConfigLocation: "Configuration" *C:\Users\Matth\AppData\Local\QtProject\qtdiag* C:\ProgramData\QtProject\qtdiag C:\bin\Python3_9_10\Lib\site-packages\PySide6 C:\bin\Python3_9_10\Lib\site-packages\PySide6\data C:\bin\Python3_9_10\Lib\site-packages\PySide6\data\QtProject\qtdiag
  DownloadLocation: "Download" *C:\Users\Matth\Downloads*
  GenericCacheLocation: "Shared Cache" *C:\Users\Matth\AppData\Local\cache*
  GenericConfigLocation: "Shared Configuration" *C:\Users\Matth\AppData\Local* C:\ProgramData C:\bin\Python3_9_10\Lib\site-packages\PySide6 C:\bin\Python3_9_10\Lib\site-packages\PySide6\data
  AppDataLocation: "Application Configuration" *C:\Users\Matth\AppData\Roaming\QtProject\qtdiag* C:\ProgramData\QtProject\qtdiag C:\bin\Python3_9_10\Lib\site-packages\PySide6 C:\bin\Python3_9_10\Lib\site-packages\PySide6\data C:\bin\Python3_9_10\Lib\site-packages\PySide6\data\QtProject\qtdiag
  AppConfigLocation: "Application Configuration" *C:\Users\Matth\AppData\Local\QtProject\qtdiag* C:\ProgramData\QtProject\qtdiag C:\bin\Python3_9_10\Lib\site-packages\PySide6 C:\bin\Python3_9_10\Lib\site-packages\PySide6\data C:\bin\Python3_9_10\Lib\site-packages\PySide6\data\QtProject\qtdiag

File selectors (increasing order of precedence):
  en_US windows winnt

Network:
  Using "Secure Channel, Windows 10.0.22000", version: 0xa0055f0

Platform capabilities: ThreadedPixmaps OpenGL ThreadedOpenGL WindowMasks MultipleWindows ForeignWindows NonFullScreenWindows NativeWidgets WindowManagement RasterGLSurface AllGLFunctionsQueryable

Style hints:
  mouseDoubleClickInterval: 550
  mousePressAndHoldInterval: 800
  startDragDistance: 10
  startDragTime: 500
  startDragVelocity: 0
  keyboardInputInterval: 400
  keyboardAutoRepeatRate: 32
  cursorFlashTime: 1060
  showIsFullScreen: 0
  showIsMaximized: 0
  passwordMaskDelay: 0
  passwordMaskCharacter: U+25CF
  fontSmoothingGamma: 1.2
  useRtlExtensions: 0
  setFocusOnTouchRelease: 0
  tabFocusBehavior: Qt::TabFocusAllControls 
  singleClickActivation: 0

Additional style hints (QPlatformIntegration):
  ReplayMousePressOutsidePopup: 1

Theme:
  Platforms requested : windows
            available : 
  Styles requested    : WindowsVista,Windows
         available    : windowsvista,Windows,Fusion
  System font         : "Segoe UI" 9
  Native file dialog

Fonts:
  General font : "Segoe UI" 9
  Fixed font   : "Courier New" 9
  Title font   : "Segoe UI" 9
  Smallest font: "Segoe UI" 9

Palette:
  QPalette::WindowText: #ff000000
  QPalette::Button: #fff0f0f0
  QPalette::Light: #ffffffff
  QPalette::Midlight: #ffe3e3e3
  QPalette::Dark: #ffa0a0a0
  QPalette::Mid: #ffa0a0a0
  QPalette::Text: #ff000000
  QPalette::BrightText: #ffffffff
  QPalette::ButtonText: #ff000000
  QPalette::Base: #ffffffff
  QPalette::Window: #fff0f0f0
  QPalette::Shadow: #ff696969
  QPalette::Highlight: #ff0078d7
  QPalette::HighlightedText: #ffffffff
  QPalette::Link: #ff0000ff
  QPalette::LinkVisited: #ffff00ff
  QPalette::AlternateBase: #ffe9e7e3
  QPalette::NoRole: #ff000000
  QPalette::ToolTipBase: #ffffffdc
  QPalette::ToolTipText: #ff000000
  QPalette::PlaceholderText: #80000000

Screens: 2, High DPI scaling: active
# 0 "\\.\DISPLAY1" Depth: 32 Primary: yes
  Manufacturer: 
  Model: 
  Serial number: 
  Geometry: 2194x1234+0+0 (native: 3840x2160+0+0) Available: 2194x1186+0+0
  Virtual geometry: 6034x1234-3840+0 Available: 6034x1186-3840+0
  2 virtual siblings
  Physical size: 597x336 mm  Refresh: 59.997 Hz Power state: 0
  Physical DPI: 93.3461,93.2845 Logical DPI: 96,96 (native: 168,168) Subpixel_None
  High DPI scaling factor: 1.75 DevicePixelRatio: 1.75
  Primary orientation: 2 Orientation: 2 Native orientation: 0

# 1 "\\.\DISPLAY5" Depth: 32 Primary: no
  Manufacturer: 
  Model: 
  Serial number: 
  Geometry: 2194x1234-3840+0 (native: 3840x2160-3840+0) Available: 2194x1186-3840+0
  Virtual geometry: 6034x1234-3840+0 Available: 6034x1186-3840+0
  2 virtual siblings
  Physical size: 597x336 mm  Refresh: 59.9367 Hz Power state: 0
  Physical DPI: 93.3461,93.2845 Logical DPI: 96,96 (native: 168,168) Subpixel_None
  High DPI scaling factor: 1.75 DevicePixelRatio: 1.75
  Primary orientation: 2 Orientation: 2 Native orientation: 0

Dynamic GL LibGL Vendor: NVIDIA Corporation
Renderer: NVIDIA GeForce RTX 2060/PCIe/SSE2
Version: 4.6.0 NVIDIA 511.79
Shading language: 4.60 NVIDIA
Format: Version: 4.6 Profile: 2 Swap behavior: 2 Buffer size (RGBA): 8,8,8,8 Depth buffer: 24 Stencil buffer: 8
Profile: None (QOpenGLFunctions_4_6)

Vulkan instance available
Supported instance extensions:
  VK_KHR_surface, version 25
  VK_KHR_win32_surface, version 5
  VK_KHR_external_memory_capabilities, version 1
  VK_KHR_external_semaphore_capabilities, version 1
  VK_KHR_external_fence_capabilities, version 1
  VK_KHR_get_physical_device_properties2, version 2
  VK_KHR_get_surface_capabilities2, version 1
  VK_KHR_device_group_creation, version 1
  VK_EXT_swapchain_colorspace, version 3
  VK_KHR_display, version 23
  VK_KHR_get_display_properties2, version 1
  VK_KHR_surface_protected_capabilities, version 1
  VK_EXT_debug_report, version 10
  VK_EXT_debug_utils, version 2
  VK_EXT_direct_mode_display, version 1
  VK_NV_external_memory_capabilities, version 1
Supported layers:
  VK_LAYER_NV_optimus, version 1, spec version 1.3.194, NVIDIA Optimus layer
  VK_LAYER_OBS_HOOK, version 1, spec version 1.2.131, Open Broadcaster Software hook
  VK_LAYER_VALVE_steam_overlay, version 1, spec version 1.2.136, Steam Overlay Layer
  VK_LAYER_VALVE_steam_fossilize, version 1, spec version 1.2.136, Steam Pipeline Caching Layer
Available physical devices:
  API version 1.3.194, vendor 0x10DE, device 0x1F08, NVIDIA GeForce RTX 2060, type 2, driver version 511.316.0  API version 1.2.177, vendor 0x8086, device 0x3E98, Intel(R) UHD Graphics 630, type 1, driver version 0.402.1472


GPU #1:
         Card name         : NVIDIA GeForce RTX 2060
       Driver Name         : nvldumdx.dll
    Driver Version         : 30.0.15.1179
         Vendor ID         : 0x10DE
         Device ID         : 0x1F08
         SubSys ID         : 0x37591028
       Revision ID         : 0x00A1

GPU #2:
         Card name         : Intel(R) UHD Graphics 630
       Driver Name         : igdumdim64.dll
    Driver Version         : 27.20.100.9664
         Vendor ID         : 0x8086
         Device ID         : 0x3E98
         SubSys ID         : 0x08591028
       Revision ID         : 0x0002

Qt Rendering Hardware Interface supported backends:
OpenGL (with default QSurfaceFormat):
  Driver Info: Device: NVIDIA Corporation NVIDIA GeForce RTX 2060/PCIe/SSE2 4.6.0 NVIDIA 511.79 Device ID: 0x0 Vendor ID: 0x0 Device type: Unknown
  Min Texture Size: 1
  Max Texture Size: 32768
  Max Color Attachments: 8
  Frames in Flight: 1
  Async Readback Limit: 1
  MaxThreadGroupsPerDimension: 65535
  MaxThreadsPerThreadGroup: 1024
  MaxThreadGroupX: 1024
  MaxThreadGroupY: 1024
  MaxThreadGroupZ: 64
  Uniform Buffer Alignment: 1
  Supported MSAA sample counts: 1,2,4,8,16,32
  Features:
    v MultisampleTexture
    v MultisampleRenderBuffer
    - DebugMarkers
    - Timestamps
    v Instancing
    - CustomInstanceStepRate
    v PrimitiveRestart
    v NonDynamicUniformBuffers
    v NonFourAlignedEffectiveIndexBufferOffset
    v NPOTTextureRepeat
    - RedOrAlpha8IsRed
    v ElementIndexUint
    v Compute
    v WideLines
    v VertexShaderPointSize
    v BaseVertex
    - BaseInstance
    v TriangleFanTopology
    v ReadBackNonUniformBuffer
    v ReadBackNonBaseMipLevel
    v TexelFetch
    v RenderToNonBaseMipLevel
    v IntAttributes
    v ScreenSpaceDerivatives
    - ReadBackAnyTextureFormat
  Texture formats: RGBA8 BGRA8 R8 R16 RG8 RED_OR_ALPHA8 RGBA16F RGBA32F R16F R32F D16 D32F BC1 BC2 BC3 ETC2_RGB8 ETC2_RGB8A1 ETC2_RGBA8 ASTC_4x4 ASTC_5x4 ASTC_5x5 ASTC_6x5 ASTC_6x6 ASTC_8x5 ASTC_8x6 ASTC_8x8 ASTC_10x5 ASTC_10x6 ASTC_10x8 ASTC_10x10 ASTC_12x10 ASTC_12x12
Vulkan:
  Driver Info: Device: NVIDIA GeForce RTX 2060 Device ID: 0x1F08 Vendor ID: 0x10DE Device type: Discrete
  Min Texture Size: 1
  Max Texture Size: 32768
  Max Color Attachments: 8
  Frames in Flight: 2
  Async Readback Limit: 2
  MaxThreadGroupsPerDimension: 65535
  MaxThreadsPerThreadGroup: 1024
  MaxThreadGroupX: 1024
  MaxThreadGroupY: 1024
  MaxThreadGroupZ: 64
  Uniform Buffer Alignment: 64
  Supported MSAA sample counts: 1,2,4,8
  Features:
    v MultisampleTexture
    v MultisampleRenderBuffer
    - DebugMarkers
    v Timestamps
    v Instancing
    - CustomInstanceStepRate
    v PrimitiveRestart
    v NonDynamicUniformBuffers
    v NonFourAlignedEffectiveIndexBufferOffset
    v NPOTTextureRepeat
    v RedOrAlpha8IsRed
    v ElementIndexUint
    v Compute
    v WideLines
    v VertexShaderPointSize
    v BaseVertex
    v BaseInstance
    v TriangleFanTopology
    v ReadBackNonUniformBuffer
    v ReadBackNonBaseMipLevel
    v TexelFetch
    v RenderToNonBaseMipLevel
    v IntAttributes
    v ScreenSpaceDerivatives
    v ReadBackAnyTextureFormat
  Texture formats: RGBA8 BGRA8 R8 R16 RG8 RED_OR_ALPHA8 RGBA16F RGBA32F R16F R32F D16 D32F BC1 BC2 BC3 BC4 BC5 BC6H BC7
Direct3D 11:
  Driver Info: Device: NVIDIA GeForce RTX 2060 Device ID: 0x1F08 Vendor ID: 0x10DE Device type: Unknown
  Min Texture Size: 1
  Max Texture Size: 16384
  Max Color Attachments: 8
  Frames in Flight: 1
  Async Readback Limit: 1
  MaxThreadGroupsPerDimension: 65535
  MaxThreadsPerThreadGroup: 1024
  MaxThreadGroupX: 1024
  MaxThreadGroupY: 1024
  MaxThreadGroupZ: 64
  Uniform Buffer Alignment: 256
  Supported MSAA sample counts: 1,2,4,8
  Features:
    v MultisampleTexture
    v MultisampleRenderBuffer
    v DebugMarkers
    v Timestamps
    v Instancing
    v CustomInstanceStepRate
    v PrimitiveRestart
    - NonDynamicUniformBuffers
    v NonFourAlignedEffectiveIndexBufferOffset
    v NPOTTextureRepeat
    v RedOrAlpha8IsRed
    v ElementIndexUint
    v Compute
    - WideLines
    - VertexShaderPointSize
    v BaseVertex
    v BaseInstance
    - TriangleFanTopology
    v ReadBackNonUniformBuffer
    v ReadBackNonBaseMipLevel
    v TexelFetch
    v RenderToNonBaseMipLevel
    v IntAttributes
    v ScreenSpaceDerivatives
    v ReadBackAnyTextureFormat
  Texture formats: RGBA8 BGRA8 R8 R16 RG8 RED_OR_ALPHA8 RGBA16F RGBA32F R16F R32F D16 D32F BC1 BC2 BC3 BC4 BC5 BC6H BC7

mliberty

I tried the example on two other machines. One has the same behavior, the other works fine without any rendering artifacts.

The other bad computer is a laptop with a 1920x1080 display and an Nvidia graphics card.

The good computer is a desktop with a 1920x1080 display and just Intel graphics.

SGaist

Hi and welcome to devnet,

Are you using the same NVIDIA driver version on both machines ?

If so, is it the latest ? If not, can you update ? If so, can you downgrade ?

mliberty

Yes, both machines with Nvidia graphics cards are running the latest and greatest Nvidia driver 511.79 released 2/14/2022. That also matches the version reported in qtdiag:

Version: 4.6.0 NVIDIA 511.79

Using Windows device manager, I disabled my Nvidia graphics card, which should force it to use the built-in Intel UHD Graphics 630. I still see the same rendering issues. I will try to reboot and also then reinstall and older Nvidia driver, say from a year ago.

mliberty

Rebooting to cleanly use the Intel graphics had no effect. The rendering issues were still the same.

I then re-enabled my nvidia card using Device Manager, and then downgraded to 471.41 from 2021.7.9. It appears to be the oldest driver that supports Win 11. Same rendering issue.

So, while there is certainly some computer-to-computer variability, it seems pretty repeatable on 2 out of my 3 computers.

@SGaist - anything else that you would recommend? I know that my example is python, but does it look right to you? Am I missing any Qt calls? Note that storing the widgets to a member is the Python-way of ensuring they aren't garbage collected...

SGaist

Nothing stands out as wrong in your code.

I am wondering whether it's related to the 0px borders that you are using.

mliberty

Interesting thought. I updated padding, padding-*, border-width, setContentsMargins, setHoriztonalSpacing, and setVerticalSpacing to all be 1 rather than zero. Same problem :(

I then completely removed all the padding, padding-*, border-width QSS specs, along with the calls to setContentsMargins, setHoriztonalSpacing, and setVerticalSpacing. Same problem :(

I have just asked Selmen d on Upwork to investigate this issue. Thanks for your help @SGaist, and I don't want to take more of your time. I will follow up here with whatever Selmen finds!

mliberty

After further investigation, we believe that this is an issue with Qt's pixel rendering on Windows. We submitted a bug:
https://bugreports.qt.io/browse/QTBUG-101047

SGaist

Thanks for the detailed analysis !