Hi!
This is a stab in the dark but I hope it will at least point you in the
right direction. :)
Some function calls trigger things that will not be done and finished
right away, but are processing asynchronously in the background. It
sounds like this might be happening here. You are requesting a change to
the layer order but I guess(!) QGIS takes its time to do so in the
background. While it is doing that, you export the map image and that
happens immediately at whatever stage the layer reordering is currently at.
For those occasions, usually there are signals that communicate the
changed state at a later point in time. Those signals can be connected
to functions to be executed (so-called "slots").
In this case *maybe*
https://qgis.org/pyqgis/master/core/QgsLayerTree.html#qgis.core.QgsLayerTree.customLayerOrderChanged
is the right signal to use?
The logic would be e.g.:
def my_export_function():
...
my_project = QgsProject.instance()
...
exporter.exportToImage(png_name, settings=canvas_settings)
...
my_tree.customLayerOrderChanged.connect(my_export_function)
# ^ no parentheses here, you pass the function object! ^
my_tree.setCustomLayerOrder(my_layers)
my_tree.setHasCustomLayerOrder(True)
...
Now the my_export_function function would be called when the
QgsLayerTree says that its custom layer order has been changed.
As I said, this might be a wrong guess or it might be a different signal
that you need to connect to, but maybe this gets you going in the right
direction.
Cheers, Hannes
On 5/25/25 19:05, AFernandez via QGIS-Developer wrote:
Hello,
I'm reordering the map layers using
my_instance = QgsProject.instance()
my_tree = my_instance.layerTreeRoot()
...
my_tree.setCustomLayerOrder(my_layers)
my_tree.setHasCustomLayerOrder(True)
This works smoothly and the map canvas looks as targeted. However, the
problem arises when calling a function to export the image. The lines
to accomplish this task read:
def my_export_function(...):
my_project = QgsProject.instance()
manager = my_project.layoutManager()
layout = QgsPrintLayout(my_project)
layout.initializeDefaults()
... (lines to set up canvas size and others)
exporter = QgsLayoutExporter(layout)
canvas_settings = exporter.ImageExportSettings()
exporter.exportToImage(png_name, settings=canvas_settings)
When the image is exported for the first time, It completely ignores
the order of the layers previously set up with 'my_layers'. The
perplexing thing is that when the function is called to export the
image for a second time (without doing anything else), the new
exported image follows the new layer order. I've been going over this
issue for the last 2 weeks but cannot figure out what controls the
layer order of the exported image or how to fix the issue.
Thanks.
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