noDataValues aren't correctly rendered when using a custom QgsRasterDataProvider

[janzandr]

What is the bug or the crash?

I want to implement a custom QgsRasterDataProvider to do some on-the-fly raster processing/manipulation. It seams that the noDataValues aren't rendered correctly. NoDataValues should be transparent, instead they are rendered as normal values.

I prepared a minimalistic example reproducing the bug. The provider simply delivers data with values 0, 1, 2, and the value 1 is set as the noDataValue.

In QGIS the layer is wrongly rendered. The gray area in the middle should be transparent:

In the Layer Properties, the noDataValue is correctly displayed:

When using the Custom Transparency Options to manually mask out values of 1, it looks correct:

Steps to reproduce the issue

The minimalistic example can be executed in the QGIS Python Console:

import numpy as np

from qgis.core import QgsRasterDataProvider, QgsProviderRegistry, QgsProviderMetadata, QgsMessageLog, Qgis, \
    QgsDataProvider, QgsRasterLayer, QgsRectangle, QgsRasterBlock, QgsCoordinateReferenceSystem


class MyRasterDataProvider(QgsRasterDataProvider):
    REFS = list()

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

    @classmethod
    def description(cls):
        return 'My raster data provider'

    @classmethod
    def providerKey(cls):
        return 'MyRasterDataProvider'

    @classmethod
    def createProvider(cls, uri, providerOptions, *args):
        flags = QgsDataProvider.ReadFlags()
        return MyRasterDataProvider(uri, providerOptions, flags)

    def bandCount(self):
        return 1

    def block(self, bandNo, boundingBox, width, height, feedback=None):
        block = QgsRasterBlock(self.dataType(bandNo), width, height)
        array = np.zeros((width, height), np.uint8)
        for x in range(width):
            for y in range(height):
                array[x, y] = int(x / width * 3)
        block.setData(array.tobytes())
        return block

    def clone(self):
        layer = QgsRasterLayer(self.dataSourceUri(), self.name(), self.providerKey())
        provider = layer.dataProvider()
        self.REFS.append((layer, provider))
        return provider

    def crs(self):
        return QgsCoordinateReferenceSystem.fromEpsgId(3857)

    def dataType(self, bandNo):
        return Qgis.DataType.Byte

    def extent(self):
        return QgsRectangle(700000, 6000000, 1700000, 7300000)  # roughly the extent of Germany

    def generateBandName(self, bandNo):
        return 'Band ' + str(bandNo)

    def isValid(self):
        return True

    def name(self):
        return self.providerKey()

    def xSize(self):
        return 100

    def ySize(self):
        return 130

    def sourceHasNoDataValue(self, bandNo):
        return True

    def sourceNoDataValue(self, bandNo):
        return 1

    def useSourceNoDataValue(self, bandNo):
        return True

    def htmlMetadata(self) -> str:
        return ''

    def sourceDataType(self, bandNo: int):
        return self.dataType(bandNo)


def register_data_provider():
    metadata = QgsProviderMetadata(
        MyRasterDataProvider.providerKey(),
        MyRasterDataProvider.description(),
        MyRasterDataProvider.createProvider)
    registry = QgsProviderRegistry.instance()
    registry.registerProvider(metadata)
    QgsMessageLog.logMessage(
        f'{MyRasterDataProvider.providerKey()} raster data provider registered', level=Qgis.MessageLevel.Info
    )

register_data_provider()
layer = QgsRasterLayer('dummy', 'my layer', MyRasterDataProvider.providerKey())
QgsProject.instance().addMapLayer(layer)

Versions

QGIS version
3.28.7-Firenze
QGIS code revision
fedae0e
Qt version
5.15.3
Python version
3.9.5
GDAL/OGR version
3.7.0
PROJ version
9.2.0
EPSG Registry database version
v10.082 (2023-02-06)
GEOS version
3.11.2-CAPI-1.17.2
SQLite version
3.41.1
PDAL version
2.5.3
PostgreSQL client version
unknown
SpatiaLite version
5.0.1
QWT version
6.1.6
QScintilla2 version
2.13.1
OS version
Windows 10 Version 2009

Active Python plugins
Coregistration
22.5.19
DataPlotly
3.9.2
ee_plugin
0.0.6
enmapboxplugin
3.13.0-alpha-0
IPyConsole
version 2.0
magnetic_bearing_measurement
0.5
nominatim_locator_filter
0.2.4
openlayers_plugin
2.0.0
qgis_stac
1.1.1
quick_map_services
0.19.33
rasterdataplotting
1.7
rastertimeseriesmanager
1.8
timeseriesviewerplugin
1.17.20210312T143004.master
vrtbuilderplugin
0.9.20210222T174536.master
zoomview
1.1.2
db_manager
0.1.20
grassprovider
2.12.99
MetaSearch
0.3.6
processing
2.12.99
sagaprovider
2.12.99

Supported QGIS version

• I'm running a supported QGIS version according to the roadmap.

New profile

• I tried with a new QGIS profile

Additional context

No response