With a master build (git commit 34c8d01), I cannot use the Halftone (Filters/Artistic) filter, it renders a whole white image layer. This filter is known to work in all 4.x DMG versions.
Created attachment 114179 [details] Top: master, Bottom: 4.0.x I can confirm this bug on OSX. You can eventually make some dots appear. it seems something on how the values are interpreted has changed. Attachment shows the two renderings. on the top is compiled master sources after forcing values to get some big circles (Default settings show a white canvas). On the bottom the default result on 4.0.x
Created attachment 114192 [details] [^ screenshot of the bug, reproductible git~master@GNU/Linux] I can confirm the bug on git~master on GNU/Linux.
As of 2d24e9a09f796466e3001510ce24944785192c95 it is working again.