Add `Color32::mul` (#5437)

Multiply two `Color32` together quickly, in gamma-space

crates/ecolor/src/color32.rs

@@ -269,3 +269,18 @@ impl Color32 {
         )
     }
 }
+
+impl std::ops::Mul for Color32 {
+    type Output = Self;
+
+    /// Fast gamma-space multiplication.
+    #[inline]
+    fn mul(self, other: Self) -> Self {
+        Self([
+            fast_round(self[0] as f32 * other[0] as f32 / 255.0),
+            fast_round(self[1] as f32 * other[1] as f32 / 255.0),
+            fast_round(self[2] as f32 * other[2] as f32 / 255.0),
+            fast_round(self[3] as f32 * other[3] as f32 / 255.0),
+        ])
+    }
+}

crates/egui/src/widgets/button.rs

@@ -158,7 +158,7 @@ impl<'a> Button<'a> {
         self
     }
 
-    /// If true, the tint of the image is the same as the text color.
+    /// If true, the tint of the image is multiplied by the widget text color.
     ///
     /// This makes sense for images that are white, that should have the same color as the text color.
     /// This will also make the icon color depend on hover state.
@@ -336,7 +336,7 @@ impl Widget for Button<'_> {
                 let tlr = image.load_for_size(ui.ctx(), image_size);
                 let mut image_options = image.image_options().clone();
                 if image_tint_follows_text_color {
-                    image_options.tint = visuals.text_color();
+                    image_options.tint = image_options.tint * visuals.text_color();
                 }
                 widgets::image::paint_texture_load_result(
                     ui,