RGBtoANSI: fixup lower grey onversions, looks reasonable now #4

src/lib/internal.h

@@ -180,7 +180,9 @@ rgb_to_ansi256(unsigned r, unsigned g, unsigned b){
   g &= GREYMASK;
   b &= GREYMASK;
   if(r == g && g == b){ // 5 MSBs match, return grey
-    return 224 + (r >> 3u);
+    r >>= 3u;
+    r += 232;
+    return r > 255 ? 255: r;
   }
   r /= 43;
   g /= 43;

src/poc/rgbbg.c

@@ -0,0 +1,49 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <locale.h>
+#include <notcurses.h>
+
+int main(void){
+  if(!setlocale(LC_ALL, "")){
+    fprintf(stderr, "Couldn't set locale\n");
+    return EXIT_FAILURE;
+  }
+  struct notcurses_options opts;
+  memset(&opts, 0, sizeof(opts));
+  opts.inhibit_alternate_screen = true;
+  struct notcurses* nc = notcurses_init(&opts, stdout);
+  if(nc == NULL){
+    return EXIT_FAILURE;
+  }
+  int y, x, dimy, dimx;
+  struct ncplane* n = notcurses_stdplane(nc);
+  ncplane_dim_yx(n, &dimy, &dimx);
+  int r , g, b;
+  r = 0;
+  g = 0x80;
+  b = 0;
+  ncplane_set_fg_rgb(n, 0x80, 0x80, 0x80);
+  for(y = 0 ; y < dimy ; ++y){
+    for(x = 0 ; x < dimx ; ++x){
+      ncplane_set_bg_rgb(n, r, g, b);
+      ncplane_putsimple(n, 'x');
+      if(g % 2){
+        if(b-- == 0){
+          ++g;
+          b = 0;
+        }
+      }else{
+        if(b++ >= 256){
+          ++g;
+          b = 256;
+        }
+      }
+    }
+  }
+  if(notcurses_render(nc)){
+    notcurses_stop(nc);
+    return EXIT_FAILURE;
+  }
+  notcurses_stop(nc);
+  return EXIT_SUCCESS;
+}

tests/internal.cpp

@@ -16,3 +16,9 @@ TEST_F(InternalsTest, RGBtoANSIWhite) {
   r = g = b = 0xff;
   EXPECT_EQ(255, rgb_to_ansi256(r, g, b));
 }
+
+TEST_F(InternalsTest, RGBtoANSIBlack) {
+  unsigned r, g, b;
+  r = g = b = 0x0;
+  EXPECT_EQ(232, rgb_to_ansi256(r, g, b));
+}