[style] Fade out windows on close

epaint/src/color.rs

@@ -129,6 +129,14 @@ impl Color32 {
     pub fn to_tuple(&self) -> (u8, u8, u8, u8) {
         (self.r(), self.g(), self.b(), self.a())
     }
+
+    /// Multiply with 0.5 to make color half as opaque.
+    pub fn linear_multiply(self, factor: f32) -> Color32 {
+        debug_assert!(0.0 <= factor && factor <= 1.0);
+        // As an unfortunate side-effect of using premultiplied alpha
+        // we need a somewhat expensive conversion to linear space and back.
+        Rgba::from(self).multiply(factor).into()
+    }
 }
 
 // ----------------------------------------------------------------------------

epaint/src/shadow.rs

@@ -1,11 +1,15 @@
 use super::*;
 
-/// A rectangular shadow with a soft penumbra.
+/// The color and fuzziness of a fuzzy shape.
+/// Can be used for a rectangular shadow with a soft penumbra.
 #[derive(Clone, Copy, Debug, Default, PartialEq)]
 #[cfg_attr(feature = "persistence", derive(serde::Deserialize, serde::Serialize))]
 pub struct Shadow {
-    // The shadow extends this much outside the rect.
+    /// The shadow extends this much outside the rect.
+    /// The size of the fuzzy penumbra.
     pub extrusion: f32,
+
+    /// Color of the opaque center of the shadow.
     pub color: Color32,
 }
 

epaint/src/tessellator.rs

@@ -420,8 +420,9 @@ fn stroke_path(
 
 fn mul_color(color: Color32, factor: f32) -> Color32 {
     debug_assert!(0.0 <= factor && factor <= 1.0);
-    // sRGBA correct fading requires conversion to linear space and back again because of premultiplied alpha
-    Rgba::from(color).multiply(factor).into()
+    // As an unfortunate side-effect of using premultiplied alpha
+    // we need a somewhat expensive conversion to linear space and back.
+    color.linear_multiply(factor)
 }
 
 // ----------------------------------------------------------------------------