First of all, clone the repository with submodules:

$ cd package
$ git clone --recurse-submodules git@github.com:nextgis/nextgisweb_qgis.git

Then install qgis_headless which is included as git submodule and requires QGIS 3.22+ and some additional libraries (see qgis_headeless/README.md for details).

$ cd nextgisweb_qgis
$ pip install -e qgis_headless

Finally, install nextgisweb_qgis into virtualenv:

$ pip install -e ./

Since original QGIS libraries do render layers in this extension, most styling and rendering options work well. However, there is a big difference between QGIS and NextGIS Web in how they compose layers. QGIS renders layers together and places labels on top of all layers. On the other hand, NextGIS Web renders layers one-by-one (or even tile-by-tile) and stacks them together on a client side. That's why, NextGIS Web rendering of QGIS styles may differ in the following ways:

• Blending options don't work;
• Labels from diffenent layers may overlap;
• Expression-driven SVG markers don't work;
• Masking doesn't work at all, as it part of a project, not of a layer.

Some rendering features require special handling on QGIS Headless library side and aren't implemented yet:

• Variables, like @mascale
• Gradients-based fills
• Labels with external SVG markers