With round join, PLRM3 and PDF 1.4 requires to paint a full round, but PDF 1.5 requires to paint a "pieslice-shaped figure". IMO we should do the latter in any case to simplify the implementation - likely "full round" is now obsolete and gives either the same or a worse result. This problem is related to the bug 688126, but we consider it as an independent problem, because it's a difference between Postscript and PDF.
Note that Adobe Reader, Apple Preview and the cairo library use the new 'pie' style round join, even for PDF-1.4 input. PDF < 1.5 and PLRM specs all warn about the rendering issues with painting the full round. So direct spec compliance with Postscript is the only situation that warrants the full round join.
Reassigning to me, as I have a patch for this in testing.
Created attachment 5658 [details] jointest3.ps This file shows a variety of joins. In particular, it shows round joins between some very short strokes, both in stroked and strokepath modes. The "stroked" version shows up as full round in ghostscript, but as a pie join in every other renderer we've tried (adobe acrobat 9, CPSI, Jaws etc). The "stroked path" version appears to always show as a full round, in Acrobat and Jaws at least. Ghostscript was changed recently to always use CPSI_mode for strokepaths. This leaves us free to change the stroke code to use 'pie' shaped rounds and we should get exactly what we want.
Revision 10320 contains a patch to fix this.