always enable 8bpc RGB for kitty, alacritty, and foot #1641

NEWS.md

@@ -9,6 +9,9 @@ rearrangements of Notcurses.
     that they will be reported by `ncplane_at_yx()`). Since no method currently
     exists to destroy a sprixel without destroying its plane, I don't think
     this will impact anyone.
+  * 8bpc RGB is unconditionally enabled if the terminal emulator is determined
+    to be Kitty, Alacritty, or foot; there is no longer any need to export
+    `COLORTERM` on these terminals.
   * Add `NCSCALE_INFLATE`.
 
 * 2.3.0 (2021-05-09) **"Triumph"**

README.md

@@ -193,6 +193,8 @@ exporting the `COLORTERM` environment variable as `truecolor` or `24bit`.
 Note that some terminals accept a 24-bit specification, but map it down to
 fewer colors.
 
+Since 2.3.1, 8bpc RGB is always enabled for Kitty, Alacritty, and foot.
+
 ### Fonts
 
 Fonts end up being a whole thing, little of which is pleasant. I'll write this

TERMINALS.md

@@ -172,6 +172,8 @@ implementing `rgb` use the 3x8bpc model; XTerm for instance:
 Thus emitting `setaf` with an RGB value close to black can result, when
 using `xterm-direct`'s `setaf` and `rgb` definitions, in a bright ANSI color.
 
+Since 2.3.1, DirectColor is always enabled for Kitty, Alacritty, and foot.
+
 ## Problematic characters
 
 Some characters seem to cause problems with one terminal or another. These

src/lib/terminfo.c

@@ -92,17 +92,20 @@ apply_term_heuristics(tinfo* ti, const char* termname, int fd){
     ti->quadrants = true;
     ti->pixel_query_done = true;
     ti->bitmap_supported = true;
+    ti->RGBflag = true;
     setup_kitty_bitmaps(ti, fd);
   }else if(strstr(termname, "alacritty")){
     ti->alacritty_sixel_hack = true;
     ti->quadrants = true;
     // ti->sextants = true; // alacritty https://github.com/alacritty/alacritty/issues/4409 */
+    ti->RGBflag = true;
   }else if(strstr(termname, "vte") || strstr(termname, "gnome") || strstr(termname, "xfce")){
     ti->sextants = true; // VTE has long enjoyed good sextant support
     ti->quadrants = true;
   }else if(strncmp(termname, "foot", 4) == 0){
     ti->sextants = true;
     ti->quadrants = true;
+    ti->RGBflag = true;
   }else if(strncmp(termname, "st", 2) == 0){
     // st had neithersextants nor quadrants last i checked (0.8.4)
   }else if(strstr(termname, "mlterm")){
@@ -140,6 +143,9 @@ void free_terminfo_cache(tinfo* ti){
 int interrogate_terminfo(tinfo* ti, int fd, const char* termname, unsigned utf8){
   memset(ti, 0, sizeof(*ti));
   ti->utf8 = utf8;
+  // allow the "rgb" boolean terminfo capability, a COLORTERM environment
+  // variable of either "truecolor" or "24bit", or unconditionally enable it
+  // for several terminals known to always support 8bpc rgb setaf/setab.
   ti->RGBflag = query_rgb();
   int colors = tigetnum("colors");
   if(colors <= 0){