term: fix coloring mess

Until now, the config file required manual adjustment for the output to
look bearable on terminals colored differently than {bgcolor: black,
fgcolor: white}. Also, it only detected RGB when COLORTERM was set, but
this is not done by most (any?) terminal emulators (sad).

To improve upon the situation, we now query the terminal for some
attributes on startup:

* OSC(10/11, ?) -> get the terminal's bg/fgcolor
* DCS(+, q, 524742) -> XTGETTCAP for the "RGB" capability (only
  supported by a few terminals, but better than nothing)
* Primary device attributes -> check if ANSI colors are supported, also
  make sure we don't block indefinitely even if the previous queries
  fail

If primary device attributes does not return anything, we hang until
the user types something, then notify the user that something went
wrong, and tell them how to fix it. Seems like an OK fallback.

(The DA1 idea comes from notcurses; since this is implemented by pretty
much every terminal emulator, we don't have to rely on slow timing hacks
to skip non-supported queries.)

1 files changed, 3 insertions, 2 deletions

diff --git a/src/config/config.nim b/src/config/config.nim
index c66e7883..678f7f7b 100644
--- a/src/config/config.nim
+++ b/src/config/config.nim
@@ -117,8 +117,9 @@ type
     minimum_contrast* {.jsgetset.}: int32
     force_clear* {.jsgetset.}: bool
     set_title* {.jsgetset.}: bool
-    default_background_color* {.jsgetset.}: RGBColor
-    default_foreground_color* {.jsgetset.}: RGBColor
+    default_background_color* {.jsgetset.}: Opt[RGBColor]
+    default_foreground_color* {.jsgetset.}: Opt[RGBColor]
+    query_da1* {.jsgetset.}: bool
 
   Config* = ref ConfigObj
   ConfigObj* = object