Ncurses: better color approximation

On terminals with only 8 colors (like with `TERM=screen`)

src/backend/curses/mod.rs

@@ -5,7 +5,7 @@
 
 use event::{Event, Key};
 use std::collections::HashMap;
-use theme::{BaseColor, Color};
+use theme::{BaseColor, Color, ColorPair};
 
 #[cfg(feature = "ncurses")]
 pub mod n;
@@ -61,7 +61,14 @@ where
     }
 }
 
-fn find_closest(color: &Color) -> i16 {
+fn find_closest_pair(pair: &ColorPair, max_colors: i16) -> (i16, i16) {
+    (
+        find_closest(&pair.front,max_colors),
+        find_closest(&pair.back, max_colors),
+    )
+}
+
+fn find_closest(color: &Color, max_colors: i16) -> i16 {
     match *color {
         Color::TerminalDefault => -1,
         Color::Dark(BaseColor::Black) => 0,
@@ -72,29 +79,45 @@ fn find_closest(color: &Color) -> i16 {
         Color::Dark(BaseColor::Magenta) => 5,
         Color::Dark(BaseColor::Cyan) => 6,
         Color::Dark(BaseColor::White) => 7,
-        Color::Light(BaseColor::Black) => 8,
-        Color::Light(BaseColor::Red) => 9,
-        Color::Light(BaseColor::Green) => 10,
-        Color::Light(BaseColor::Yellow) => 11,
-        Color::Light(BaseColor::Blue) => 12,
-        Color::Light(BaseColor::Magenta) => 13,
-        Color::Light(BaseColor::Cyan) => 14,
-        Color::Light(BaseColor::White) => 15,
-        Color::Rgb(r, g, b) => {
+        Color::Light(BaseColor::Black) => 8 % max_colors,
+        Color::Light(BaseColor::Red) => 9 % max_colors,
+        Color::Light(BaseColor::Green) => 10 % max_colors,
+        Color::Light(BaseColor::Yellow) => 11 % max_colors,
+        Color::Light(BaseColor::Blue) => 12 % max_colors,
+        Color::Light(BaseColor::Magenta) => 13 % max_colors,
+        Color::Light(BaseColor::Cyan) => 14 % max_colors,
+        Color::Light(BaseColor::White) => 15 % max_colors,
+        Color::Rgb(r, g, b) if max_colors >= 256 => {
             // If r = g = b, it may be a grayscale value!
             if r == g && g == b && r != 0 && r < 250 {
+                // Grayscale
                 // (r = g = b) = 8 + 10 * n
                 // (r - 8) / 10 = n
                 //
                 let n = (r - 8) / 10;
                 (232 + n) as i16
             } else {
+                // Generic RGB
                 let r = 6 * u16::from(r) / 256;
                 let g = 6 * u16::from(g) / 256;
                 let b = 6 * u16::from(b) / 256;
                 (16 + 36 * r + 6 * g + b) as i16
             }
         }
-        Color::RgbLowRes(r, g, b) => i16::from(16 + 36 * r + 6 * g + b),
+        Color::Rgb(r, g, b) => {
+            let r = if r > 127 { 1 } else { 0 };
+            let g = if g > 127 { 1 } else { 0 };
+            let b = if b > 127 { 1 } else { 0 };
+            (r + 2 * g + 4 * b) as i16
+        }
+        Color::RgbLowRes(r, g, b) if max_colors >= 256 => {
+            i16::from(16 + 36 * r + 6 * g + b)
+        }
+        Color::RgbLowRes(r, g, b) => {
+            let r = if r > 2 { 1 } else { 0 };
+            let g = if g > 2 { 1 } else { 0 };
+            let b = if b > 2 { 1 } else { 0 };
+            (r + 2 * g + 4 * b) as i16
+        }
     }
 }

src/backend/curses/n.rs

@@ -1,7 +1,7 @@
 extern crate ncurses;
 
 use self::ncurses::mmask_t;
-use self::super::{find_closest, split_i32};
+use self::super::split_i32;
 use backend;
 use event::{Event, Key, MouseButton, MouseEvent};
 use libc;
@@ -17,7 +17,9 @@ use vec::Vec2;
 
 pub struct Backend {
     current_style: Cell<ColorPair>,
-    pairs: RefCell<HashMap<ColorPair, i16>>,
+
+    // Maps (front, back) ncurses colors to ncurses pairs
+    pairs: RefCell<HashMap<(i16, i16), i16>>,
 
     key_codes: HashMap<i32, Event>,
 
@@ -25,6 +27,10 @@ pub struct Backend {
     event_queue: Vec<Event>,
 }
 
+fn find_closest_pair(pair: &ColorPair) -> (i16, i16) {
+    super::find_closest_pair(pair, ncurses::COLORS() as i16)
+}
+
 /// Writes some bytes directly to `/dev/tty`
 ///
 /// Since this is not going to be used often, we can afford to re-open the
@@ -89,11 +95,13 @@ impl Backend {
         Box::new(c)
     }
 
+
     /// Save a new color pair.
     fn insert_color(
-        &self, pairs: &mut HashMap<ColorPair, i16>, pair: ColorPair
+        &self, pairs: &mut HashMap<(i16, i16), i16>, (front, back): (i16, i16)
     ) -> i16 {
         let n = 1 + pairs.len() as i16;
+
         let target = if ncurses::COLOR_PAIRS() > i32::from(n) {
             // We still have plenty of space for everyone.
             n
@@ -104,12 +112,8 @@ impl Backend {
             pairs.retain(|_, &mut v| v != target);
             target
         };
-        pairs.insert(pair, target);
-        ncurses::init_pair(
-            target,
-            find_closest(&pair.front),
-            find_closest(&pair.back),
-        );
+        pairs.insert((front, back), target);
+        ncurses::init_pair(target, front, back);
         target
     }
 
@@ -118,11 +122,12 @@ impl Backend {
         let mut pairs = self.pairs.borrow_mut();
 
         // Find if we have this color in stock
-        if pairs.contains_key(&pair) {
+        let (front, back) = find_closest_pair(&pair);
+        if pairs.contains_key(&(front, back)) {
             // We got it!
-            pairs[&pair]
+            pairs[&(front, back)]
         } else {
-            self.insert_color(&mut *pairs, pair)
+            self.insert_color(&mut *pairs, (front, back))
         }
     }
 

src/backend/curses/pan.rs

@@ -1,7 +1,7 @@
 extern crate pancurses;
 
 use self::pancurses::mmask_t;
-use self::super::{find_closest, split_i32};
+use self::super::split_i32;
 use backend;
 use event::{Event, Key, MouseButton, MouseEvent};
 use std::cell::{Cell, RefCell};
@@ -13,7 +13,7 @@ use vec::Vec2;
 pub struct Backend {
     // Used
     current_style: Cell<ColorPair>,
-    pairs: RefCell<HashMap<ColorPair, i32>>,
+    pairs: RefCell<HashMap<(i16, i16), i32>>,
 
     key_codes: HashMap<i32, Event>,
 
@@ -24,6 +24,10 @@ pub struct Backend {
     window: pancurses::Window,
 }
 
+fn find_closest_pair(pair: &ColorPair) -> (i16, i16) {
+    super::find_closest_pair(pair, pancurses::COLORS() as i16)
+}
+
 impl Backend {
     pub fn init() -> Box<Self> {
         ::std::env::set_var("ESCDELAY", "25");
@@ -62,8 +66,8 @@ impl Backend {
     /// Save a new color pair.
     fn insert_color(
         &self,
-        pairs: &mut HashMap<ColorPair, i32>,
-        pair: ColorPair,
+        pairs: &mut HashMap<(i16,i16), i32>,
+        (front, back): (i16, i16),
     ) -> i32 {
         let n = 1 + pairs.len() as i32;
 
@@ -78,18 +82,15 @@ impl Backend {
             pairs.retain(|_, &mut v| v != target);
             target
         };
-        pairs.insert(pair, target);
-        pancurses::init_pair(
-            target as i16,
-            find_closest(&pair.front),
-            find_closest(&pair.back),
-        );
+        pairs.insert((front, back), target);
+        pancurses::init_pair(target as i16, front, back);
         target
     }
 
     /// Checks the pair in the cache, or re-define a color if needed.
     fn get_or_create(&self, pair: ColorPair) -> i32 {
         let mut pairs = self.pairs.borrow_mut();
+        let pair = find_closest_pair(&pair);
 
         // Find if we have this color in stock
         if pairs.contains_key(&pair) {