Qgis3 port is very slow and unresponsive

[Malauch]

Since qgis3 port verions 3.0 I noticed that it is very unresponsive. I even created the ticket in the past: #56169 However, official binaries works fast. Today I found the time to make some experiments and try to compile qgis3 port with qt59. Now I can confirm that this is a culprint for slowing down of qgis3 port. Additionaly qt59 fixes other problem with no option to resize modal windows: #56911. Naturally it also introduce some new bugs like huge mouse cursors (for addint new features and etc.).

For now running qgis3 port with qt59 is only workaround to make it usable for serious work. Therefore It would be nice to have convienient option to +qt59 variant. Please add this variant to the port.

To Install qgis3 port with qt59 I had to manually edited two ports definition:

1. Uninstall all ports and macports files.
2. To qgis3 port I added these lines: changeset:312eec49096c92819071c3e87bea0ef9a562eed8/macports-ports
3. I also had to Install older version of py-pyqt5 port. I installed 5.9.2 version. The recent version just install qt5 port which makes conflict with qt59.

[Veence (Vincent)]

I’m going to do this if you request it, but I’m a bit surprised, because the QGis3 I run on my computer has been linked with Qt 5.10 and seems to work normally. Well, I agree modal windows cannot be resized, but it hasn't really bugged me until now. However, what do you think work slow? Do you have any specific example to support this?

[Malauch]

It's easiest to spot the difference in speed when adding very quickly new points to point layer. With QT 5.9 all points shows immediately on canvas, with QT 5.10 it's shows with a lot of lag. Naturally it's just a test to show a problem, not a real task. However when editing medium or large project that lag is visible and very annoying when panning the canvas, zoom in, zoom out. Sometimes when panning, some part of map is blank for 1-2 seconds (all layers are local files with vectors).

I'm curious about how it works with QT 5.11 but it's not on a macports yet.

[Veence (Vincent)]

Ok. A qt59 is feasible, but some other packages need to be updated as well, such as qca-qt and most importantly py36-qt5 which currently has no option to build on a backward version of Qt.