QGIS » QGIS Application

Hi Leyan, I can reproduce this behavior in QGIS 2.0 Dufour and master before simplification was merged.

When user changes the visibility of layer while it is being rendered and repeatedly user changes the zoom with mouse wheel, then the layer disappears or it is rendered even with visibility disabled.

I had already seen before before simplification was merged. Can you confirm it please ?
Recently I tested the multi-thread rendering branch of Martin Dobias and these issue work fine.

Yes, while a raster layer is being rendered I can not check in legend (the application is locked), but while a vector layer is drawing I can edit the legend, and then sometimes QGIS goes crazy :-)

Alvaro

OK, I can actually reproduce the issue in QGis 2.0.1, so I guess it is not strictly speaking a regression. However, I do think it happens much more frequently with master, I don't remember having so many issues before. What led me to think it is a regression is that by disabling the geometry simplification, the issue disappears.

I currently have a project where I can reliably trigger this bug each time I toggle the visibility of a layer, which means I have to keep the "Layer order" panel open to manage the visibility of my layers. It is maybe due to my small config, I am doing this on an average laptop with reasonably big layers (around 30 000 elements).

Alvaro: I think we are not talking about the same issue. I learned a long time ago not to touch anything while a layer was rendered, but here it fails just as if the click was not taken into account. No need to zoom in/out, pan or do anything, the map is simply not redrawn and the "Layer order" state is not changed. This never happens two times in a row, which means that I can always change the state by clicking three times: first change (ignored), revert to initial state, then change again, but still, not very nice to explain to the users ... It also never happened while using the "Layer order" panel to change the visibility.

Anyway, maybe not a blocker, but I still think it is an important usability issue as changing the layer visibility is a very basic and common operation. I will try multithreading and check if it improves things, I haven't pulled the branch yet.

Giovanni: I don't use raster data, so I don't know if they would be affected as well. I will check.

Martin Dobias wrote:

This should have nothing to do with geometry simplification. This is mainly about having those "qApp->processEvents()" calls in the rendering code which disrupt the code path to something like that.

Since the multi-threaded rendering should fix this by design and it is not a regression, changing the priority to low.

Thanks Martin, I think so, I tested your branch with multi-threaded rendering and this issue disappears.
Would be good to change the title of the issue to avoid confusions ?