Rationalize dark/light mode heuristic

[krobelus]

I'm implementing dark/light mode detection (reusing only xterm-colors for now since I'm using a different querying implementation).

I'd like to understand what's the significance of the logic in theme_mode() as opposed to using if background.perceived_lightness() { Dark } else { Light }.
I haven't actually tried color values other than 000000/ffffff so maybe it's very obvious.

If I simplify the heuristics as follows, cargo test still passes.

diff --git a/crates/terminal-colorsaurus/src/lib.rs b/crates/terminal-colorsaurus/src/lib.rs
index 2aa77dd..88543fd 100644
--- a/crates/terminal-colorsaurus/src/lib.rs
+++ b/crates/terminal-colorsaurus/src/lib.rs
@@ -111,14 +111,10 @@ pub enum ThemeMode {
 impl ColorPalette {
     /// Determines if the terminal uses a dark or light background.
     pub fn theme_mode(&self) -> ThemeMode {
-        let fg = self.foreground.perceived_lightness();
-        let bg = self.background.perceived_lightness();
-        if bg < fg {
+        if self.background.perceived_lightness() < 0.5 {
             ThemeMode::Dark
-        } else if bg > fg || bg > 0.5 {
-            ThemeMode::Light
         } else {
-            ThemeMode::Dark
+            ThemeMode::Light
         }
     }
 }

[tautropfli]

I'm implementing dark/light mode detection.

That's really cool to see 😍

Huh, that's a good catch, the tests should definitely have a case for this 😅

I think I was mostly concerned with themes that have a very light foreground color and a darker (but still considered light) background color. I would consider such themes dark, although that is debatable. An example of such a theme is: rgb:aaff/aaff/aaff as background and white as foreground.

From a quick search, such themes don't seem to exist, so maybe your simplification is the right way to go :)

[krobelus]

I went with the simple version for now; if a user complains I'll follow up. I found that NeoVim also uses OSC 11 but Helix uses Contour's CSI 997. Using the latter might be reasonable, but the spec is a little bit [ambiguous](contour-terminal/contour#1659 (comment)), so I'm not sure if that's really better.

Huh, that's a good catch, the tests should definitely have a case for this 😅 I think I was mostly concerned with themes that have a very light foreground color and a darker (but still considered light) background color. I would consider such themes dark, although that is debatable. An example of such a theme is: `rgb:aaff/aaff/aaff` as background and white as foreground.

That case would be covered by if fg < bg { Light } else { Dark } which is still simpler than our existing heuristic. I'd prefer to get by with as little query traffic as possible, since this is sent on every prompt -- which is a minor argument for Contour protocol I guess