[Therion] Include additional symbols in the legend

[Tarquin Wilton-Jones]

On 22/10/2020 12:00, Tarquin Wilton-Jones via Therion wrote:
> On 22/10/2020 11:44, Martin Sluka via Therion wrote:
>> Sorry, invisible symbols are not included in legend.
> 
> you might be able to include a custom symbol that looks the same, which
> chooses to draw nothing when not in the legend. that's quite a hack though.

Should be this easy, I think (not that I have tested it):

text en "point u:placeholder1" "the title you want"
code metapost
  def p_u_placeholder1 (expr P,R,S,A)=
    T:=identity shifted P;
  enddef;
  initsymbol("p_u_placeholder1");
  def p_u_placeholder1_legend (expr P,R,S,A)=
    p_therealsymbolyouwanted_SKBB(P,R,S,A);
  enddef;
endcode

Now on your plan, add a point "u" -subtype placeholder1