tabs: idle tabs you can actually read across the room

Seen next to the accent, the first plate was too polite to do the job it was
added for: a 30% lift off the background under labels in the same #45454a the
idle frames use. From another monitor the strip still read as one dark band
with a blue block in it.

Both ends move. tab_idle leaves the ambient chrome grey and becomes #8a8a95,
because a tab you are not in is a place to go and has to be legible at a
glance, where a dimmed pane border only has to be findable. The plate follows
it to 43%, which is not a taste constant but a contrast ratio: the same step
taken from a dark background upward and a light one downward lands at about
1.9:1 either way, so paper's #bdbebe on near-white and the default's #3b3b40
on black are the same amount of plate.

The six themes in contrib named their idle tab colour as their frame grey, so
each gets the same move in its own family -- 40% of the way from that grey to
the colour the theme writes text in -- and their plates follow by derivation:
amber #a67c26, mono #909090, paper #666a6e, phosphor #4a9c5d, slate #70789c,
sl0p the house #8a8a95. Nobody who named a colour loses it; the derivation
only ever fills in a theme's silence.

1 files changed, 17 insertions, 10 deletions

diff --git a/src/config.c b/src/config.c
index d729287..d2b89b7 100644
--- a/src/config.c
+++ b/src/config.c
@@ -1058,14 +1058,21 @@ void config_defaults(config_t *c) {
   c->tab_active_fg = ink;
   c->tab_active_bg = accent;
   c->tab_active_hover_fg = bright;
-  c->tab_idle = dim;
-  /* A plate under the tabs you are not in. Barely off the background and in
-   * the label's own grey: enough that a tab is a shape with edges, not enough
-   * to compete with the active tab's accent fill -- the strip has one
-   * highlight and this is not it. It also gives the active fill something to
-   * be brighter *than*, which on a strip of short labels is most of how the
-   * eye finds it. */
-  c->tab_idle_bg = blend(c->default_bg, dim, 30);
+  /* Brighter than the ambient chrome grey the rest of the idle furniture uses
+   * (`dim`, on frames and titles): a tab you are not in is a place to go, and
+   * has to be readable at a glance from across the screen, where a dimmed
+   * pane border only has to be findable. */
+  c->tab_idle = rgb(0x8a, 0x8a, 0x95);
+  /* A plate under the tabs you are not in, in the label's own grey. Enough
+   * that a tab is a shape with edges rather than a word on the background,
+   * and enough to give the active fill something to be brighter *than* --
+   * which on a strip of short labels is most of how the eye finds the tab it
+   * is in -- while staying a plate rather than a second highlight. The
+   * fraction is a contrast ratio in disguise: 43% of the way from the
+   * background to the label lands about 1.9:1 against that background whether
+   * the theme is black-on-dark or white-on-light, because the same step is
+   * being taken in opposite directions. */
+  c->tab_idle_bg = blend(c->default_bg, c->tab_idle, 43);
   c->tab_hover = accent;
   c->prefix_fg = ink;
   c->prefix_bg = accent;
@@ -2493,13 +2500,13 @@ static bool load_into(config_t *c, const char *path, int depth, char *err,
      * split apply_scrolled makes. */
     if (!kdl_child(theme, "tab_status_fg"))
       c->tab_status_fg = blend(c->tab_count, c->tab_hover, 40);
-    /* The idle tab plate, on the same terms: a third of the way from the
+    /* The idle tab plate, on the same terms: 43% of the way from the
      * theme's background to the grey it writes idle tab labels in. Every
      * theme defines both, so each gets a plate in its own family -- paper
      * lightens, phosphor greens -- and a theme that wants the bare strip back
      * says `tab_idle_bg` in its own default_bg rather than editing this. */
     if (!kdl_child(theme, "tab_idle_bg"))
-      c->tab_idle_bg = blend(c->default_bg, c->tab_idle, 30);
+      c->tab_idle_bg = blend(c->default_bg, c->tab_idle, 43);
     /* The alternate band, on the same terms. A tenth of the way from the
      * tab bar's own background toward the accent: enough to read as a
      * different row at a glance, not enough to read as a highlight. */