I have created grayscale piecharts in QGIS 3.14 Pi on Win10 with geometry generator. So the piecharts are vectors, created with the expression editor, using the
wedge_buffer expression. I created a print layout and exported it to a pdf. I opened this pdf in a vector graphic software (Affinity Designer). All elements are separately saved, can be selected and changed accordingly. When I zoom in, most elements behave as expected: as vectors, they don't show a pixel structure, even small dots are shown as perfect circles. A few lines, however, are shown with a pixel structure, see on the left of this screenshot:
I have also tried to export the layout as SVG, but it seems the structure is too complex and the exported image is full of errors. So I have to export as pdf. The problem is not related to Affinity Designer as I have the same effect when opening the exported pdf with InkScape or with a pdf-Viewer. This is strange as I created this pattern with the geometry generator and a line fill pattern, see the next screenshot:
It seems that only lines created with the line fill pattern behave in this way, regardless of the angle. Other straight lines (e.g. borders of the piechart's slices) are rendered correctly and can be zoomed in without showing a pixel pattern.
So the question is: is there a way to avoid this pixelation of vector layers in an exported pdf?