Htydjtk

How to draw a lemniscate in Asymptote? There is an answer here:
How to draw lemniscate with TikZ
However, if run asymptote after running pdflatex, I get the following error message:

Error: /undefined in .setopacityalpha

Operand stack:

   0.5

Execution stack:

   %interp_exit   .runexec2   --nostringval--   --nostringval--   --nostringval--   2   %stopped_push   --nostringval--   --nostringval--   --nostringval--   false   1   %stopped_push   2045   1   3   %oparray_pop   2044   1   3   %oparray_pop   --nostringval--   2025   1   3   %oparray_pop   1884   1   3   %oparray_pop   --nostringval--   %errorexec_pop   .runexec2   --nostringval--   --nostringval--   --nostringval--   2   %stopped_push   --nostringval--

Dictionary stack:

   --dict:967/1684(ro)(G)--   --dict:0/20(G)--   --dict:82/200(L)--

Current allocation mode is local

Current file position is 31005

GPL Ghostscript 9.26: Unrecoverable error, exit code 1                                                                                                                                                                                       

/opt/texlive/2018/texmf-dist/asymptote/plain_shipout.asy: 87.10: runtime: shipout failed                                                                                                                                                     

Error: /undefined in .setopacityalpha                                                                                                                                                                                                        

Operand stack:                                                                                                                                                                                                                               

   0.2                                                                                                                                                                                                                                       

Execution stack:                                                                                                                                                                                                                             

   %interp_exit   .runexec2   --nostringval--   --nostringval--   --nostringval--   2   %stopped_push   --nostringval--   --nostringval--   --nostringval--   false   1   %stopped_push   2045   1   3   %oparray_pop   2044   1   3   %oparray_pop   --nostringval--   2025   1   3   %oparray_pop   1884   1   3   %oparray_pop   --nostringval--   %errorexec_pop   .runexec2   --nostringval--   --nostringval--   --nostringval--   2   %stopped_push   --nostringval--              

Dictionary stack:                                                                                                                                                                                                                            

   --dict:967/1684(ro)(G)--   --dict:0/20(G)--   --dict:82/200(L)--                                                                                                                                                                          

Current allocation mode is local                                                                                                                                                                                                             

Current file position is 38506                                                                                                                                                                                                               

GPL Ghostscript 9.26: Unrecoverable error, exit code 1                                                                                                                                                                                       

/opt/texlive/2018/texmf-dist/asymptote/plain_shipout.asy: 87.10: runtime: shipout failed        

Wow.

After a lot of digging I found this bug report (which isn't actually a bug) which suggests that GhostScript (which is called by Asymptote) runs into problems when opacity is used along the the -dSAFER option. This option assures that no PostScript code which could be harmful to the system is executed. Enabling this option makes the opacity fail. If you change the line fpen=lightred+opacity(0.5); to fpen=lightred;//+opacity(0.5); and pen fpen=lightgreen+opacity(0.2); to pen fpen=lightgreen;//+opacity(0.2); (commenting out the opacity) the picture is generated:

but it's not what you'd expect. And if you enable the opacity the problem persists because Asymptote calls GhostScript with -dSAFER by default since 2008 (from the change log):

commit 407a627a5d18b773739a9535b486b8a177dd7c49

Author: John Bowman <bowman@ualberta.ca>

Date:   Mon Jun 23 11:00:40 2008 -0600



    By default run gs with -dSAFER.

After more digging through code and documentation looking for opacity without success, I searched for safe and voilà:

there is a -nosafe option which you can (when you trust the code your are executing) pass to asy so that the opacity will work.

So you can use the same code from the answer you linked (How to draw lemniscate with TikZ) and compile the document with:

pdflatex cassini.tex

asy -nosafe cassini-*asy

pdflatex cassini.tex

and it will work :)