Automatically switch into a "light mode" on light backgrounds

src/styles.rs

@@ -27,10 +27,19 @@ use Subtype::*;
 
 impl Theme {
 	pub fn from_palette(palette: Palette) -> Self {
+		let base_color = img_color_to_iced(palette.dominant_color());
+		let luma = relative_lum(base_color);
+		let text_color = if luma > 0.2 {
+			Color {
+				a: 0.8,
+				..Color::BLACK
+			}
+		} else {
+			Color::WHITE
+		};
 		Theme {
-			base_color: img_color_to_iced(palette.dominant_color()),
-			text_color: Color::WHITE,
 			subtype: Base,
+			base_color, text_color,
 		}
 	}
 
@@ -119,3 +128,17 @@ fn img_color_to_iced(color: &Rgb<u8>) -> Color {
 		a: 1.
 	}
 }
+
+pub fn relative_lum(color: Color) -> f32 {
+	let mut t = [color.r, color.g, color.b]
+		.into_iter()
+		.map(|val| {
+			if val < 0.03928 {
+				val / 12.92
+			} else {
+				((val+0.055)/1.055).powf(2.4)
+			}
+		});
+
+	0.2126 * t.next().unwrap() + 0.7152 * t.next().unwrap() + 0.0722 * t.next().unwrap()
+}