True color colon syntax

[mintty]

About Querying the Terminal: the response should actually look like ...;48:2::1:2:3m - note the double colon which allows a position for the optional color space value.

[SlySven]

Yeah, for reference the documentation is in https://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-T.416-199303-I!!PDF-E&type=items take a look at page 49 of 77 (confusingly numbered 41!) - unfortunately many interpretations forget about the second sub-parameter after the first one of 2 (or 3 or 4) and it isn't optional unless one is specifying a black which has all of the red, green and blue components as zero! Using a semi-colon as the sub-parameter separator is just so broken as it makes it so very hard to interpret an incoming code sequence...!

[kurahaupo]

(edited; sorry, the first semicolon was a typo)
@SlySven Generally one gets eitherCSI 48 : 2 : colourspace : red : green : blue m or CSI 48 ; 2 ; red ; green ; blue m . That is, the colourspace slot depends on which separator is used. The terminals that use : tend to stick more closely to the IEC spec, while those that use ; omit the colourspace but cannot omit "default" trailing values.

In practice, one can read a semicolon-separated sequence simply by looking at each element to determine how many additional elements to consume:

• If you receive 38 or 48, then take then next element as a type indicator.
  Then if that type indicator is:
  • 2 or 3, take 3 more element (for R,G,B or C,M,Y);
  • 4, take 4 more elements (for C,M,Y,K);
  • 5, take one more element (for the palette index).

I grant you that this isn't particularly robust, as it will fail if a new colourspace code is introduced. But if I had to guess, I'd speculate that the next colourspace to be added would be RGBA, so it's probably reasonable to assume that an unknown colourspace takes 4 elements.

[mintty]

There is no hybrid syntax (neither specified nor legacy) where the first separator would be ; and the others :
Standard syntax is colon-only, and you would need to swallow as many sub-parameters as are separated with colons, whether their number fits the type or not. Heuristics would apply to legacy semicolon syntax only.