For proofing metafonts, gray.mf (and black.mf) need to be compiled (I think). Otherwise the font proof dvi file will show only the control dots and not the actual shape of a glyph.
I will attach an example metafont file (from 21st page of the tutorial at http://metafont.tutorial.free.fr/).
If you compile that (mf beta.mf && gftodvi beta.2602gf) you get a beta.dvi file that you can view. It should show a curly beta glyph in halftone. However if the gray font is not compiled and in the right place you will only see the control points.
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what it looks like here
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what it should look like
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how okular-4.2 fails to show it properly. xdvi DOES show it properly, so this seems to be an okular problem.
Marijn - please assign your own bugs and describe the category/package or eclass or whatever in the Summary.
okular-4.2 fails to display dvi file correctly
As we spoke on #-kde please open upstream bug describing the issue. Give them some nice screenshot (note they require them as attachments in their bugzie and dont like links to our attachments). Add URL here containing the link to the upstream bug and close this one as upstream.
Upstream bug report: https://bugs.kde.org/show_bug.cgi?id=203559