QgsLayoutExporter export png file failed.

[hjcook]

What is the bug or the crash?

env: Ubuntu 20 64bit,qgis 3.26

When I export layout to png file with qgis python ,it's can export png file successful,but png file did not draw layer from postgis,it's only draw the layer from shp file,and reported a error :

"ERROR 6: The PNG driver does not support update access to existing datasets."

export code:
exporter = QgsLayoutExporter(layout)
imageSettings=QgsLayoutExporter.ImageExportSettings()
exporter.exportToImage(os.path.join(PROJECT_PATH,outFile), imageSettings)

Steps to reproduce the issue

Versions

QGIS 3.26

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

[nicogodet]

Could you please try on 3.28.3 ?
Share a sample project to reproduce ?

See also: https://gis.stackexchange.com/questions/360254/pyqgis-exporting-print-layout-error-6-the-png-driver-does-not-support-update

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[github-actions]

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[tsmcgrath]

Re-opening. I am exporting 400 maps in an interactive Python console loop and I'm now getting this error.
ERROR 6: The PNG driver does not support update access to existing datasets.

On MacOS, Mac M1, Sequoia 15.11, QGIS 3.40
It's not failing and the exported PNG's look fine. I'll work on getting a repro in place.

[agiudiceandrea]

@tsmcgrath, the "The PNG driver does not support update access to existing datasets." error message is thrown by the GDAL/OGR library because QgsLayoutExporter.exportToImage

QGIS/src/core/layout/qgslayoutexporter.cpp

Line 1746 in 6f4df5d

gdal::dataset_unique_ptr outputDS( GDALOpen( file.toUtf8().constData(), GA_Update ) );

tries to "update" the already exported image file in order to add the georeferencing information inside it, while this is not possibile for the "PNG" GDAL driver.
Since the error doesn't actually affects the exporting functionality, you can avoid it to be displayed just following the advice at https://gis.stackexchange.com/questions/360254/pyqgis-exporting-print-layout-error-6-the-png-driver-does-not-support-update as already suggested in a previous comment.

Anyway, it looks like the error message doesn't show up using QGIS 3.40.2 with GDAL/OGR 3.9.3 on my Windows 10 system. Where exactly is the error message displayed on your system?

[tsmcgrath]

I am using the 3.40.1 build from the conda builder releases because it runs natively on a Mac ARM:
https://github.com/opengisch/qgis-conda-builder/releases

But, I have to launch QGIS from a command line and it is in that command terminal window that I see the errors scroll by when I'm running map image exports. I will see if it recurs with 3.40.2.

[agiudiceandrea]

Hi @rouault, do you think it would be useful and worth to wrap gdal::dataset_unique_ptr outputDS( GDALOpen( file.toUtf8().constData(), GA_Update ) );

QGIS/src/core/layout/qgslayoutexporter.cpp

Line 1746 in 6f4df5d

gdal::dataset_unique_ptr outputDS( GDALOpen( file.toUtf8().constData(), GA_Update ) );

inside

  CPLPushErrorHandler( CPLQuietErrorHandler );
  CPLErrorReset();

  CPLPopErrorHandler();

since it tries to open indiscriminately any file format in "update mode", while it is not possible for many of them?