[QGIS-Developer] QGis rendering anti-aliasing, subpixel

[lars lingner]

Hello QGis developers,

In one of my QGis projects the mapstyle is using map units (meter,
epsg:3857) to style roads. But the lines are looking somehow blurred. On
nearly horizontal or vertical lines, you can also see hachures. I
collected some images [1].

The results are consistent, whether I view it in QGis desktop, the
result as an WMS request from QGis Server or as output from QGis composer.

In a discussion on German FOSSGIS list [2] there was a hint that using a
other unit in mapstyle e.g. millimeters, the result should look better.
And indeed, if the lines are at least 1 pixel, the rendered image is
looking much better.

How does the QGis rendering engine compare to MapServer or Mapnik in
regards of smooth rendering, anti-aliasing, sub-pixel-rendering?

I know MapServer and Mapnik are using AGG [3] for rendering. QGis is
using QT. Are there any options, either in QGis or QT, I can play with
to influence the render quality? Would QGis in general be able to render
objects with tiny pixel width?

Should I prefer millimeter over mapunits is my map styles from now on?

I'm using QGis 2.18.13 on linux/ubuntu, but also latest QGis3 is showing
the same result.


Thanks for listening,

Lars


[1] https://imgur.com/a/QINrq
[2]
https://lists.fossgis.de/pipermail/fossgis-talk-liste/2017-October/008843.html
[3] http://www.antigrain.com/