Bug report #20104: GDAL data provider cache is not cleared after triggerRepaint - QGIS Application - QGIS Issue Tracking

Bug report #20104

GDAL data provider cache is not cleared after triggerRepaint

Added by Radek Pasiok about 6 years ago. Updated about 6 years ago.

Status:	Closed
Priority:	Normal
Assignee:	Even Rouault
Category:	Data Provider
Affected QGIS version:	3.3(master)	Regression?:	No
Operating System:	Observed on Windows 7 and Ubuntu 18	Easy fix?:	No
Pull Request or Patch supplied:	No	Resolution:
Crashes QGIS or corrupts data:	No	Copied to github as #:	27926

Description

While porting Serval plugin [1] to QGIS 3.2 I have discovered that after a raster datasource is modified and triggerRepaint() is called [2] the provider cache is not cleared properly. As a consequence, map canvas will display old and new raster cells values at different zoom levels.

When the provider cache is not used, i.e. when QgsGdalProvider::getCachedGdalHandles would be set to only return false, then canvas properly display new cell values at all zoom levels.

Steps to reproduce:

1. Add a raster to QGIS project, for example band1_byte_ct_epsg4326.tif from QGIS test data.
2. In the Python console run:

rlyr = iface.activeLayer()
rdp = rlyr.dataProvider()
dtype = rdp.dataType(1)

rdp.setEditable(True)
rblock = QgsRasterBlock(dtype, 1, 1)
rblock.setValue(0, 0, 255)
rdp.writeBlock(rblock, 1, 0, 0)
rdp.setEditable(False)

rlyr.triggerRepaint()

3. Zoom in and out a bit to left upper raster corner to see different values of the first cell at different zoom levels.

[1] https://github.com/erpas/serval/tree/QGIS_3_port
[2] https://github.com/erpas/serval/blob/a7ebbaf7653715ebdcaf7b59ee9d069ce895a91b/serval.py#L366