Foreground function for Container Widget and WidgetExt

druid/src/widget/container.rs

@@ -30,6 +30,7 @@ struct BorderStyle {
 /// A widget that provides simple visual styling options to a child.
 pub struct Container<T> {
     background: Option<BackgroundBrush<T>>,
+    foreground: Option<BackgroundBrush<T>>,
     border: Option<BorderStyle>,
     corner_radius: KeyOrValue<RoundedRectRadii>,
 
@@ -41,6 +42,7 @@ impl<T: Data> Container<T> {
     pub fn new(child: impl Widget<T> + 'static) -> Self {
         Self {
             background: None,
+            foreground: None,
             border: None,
             corner_radius: 0.0.into(),
             child: WidgetPod::new(child).boxed(),
@@ -77,6 +79,36 @@ impl<T: Data> Container<T> {
         self.background = None;
     }
 
+    /// Builder-style method for setting the foreground for this widget.
+    ///
+    /// This can be passed anything which can be represented by a [`BackgroundBrush`];
+    /// notably, it can be any [`Color`], a [`Key<Color>`] resolvable in the [`Env`],
+    /// any gradient, or a fully custom [`Painter`] widget.
+    ///
+    /// [`Key<Color>`]: crate::Key
+    /// [`Painter`]: super::Painter
+    pub fn foreground(mut self, brush: impl Into<BackgroundBrush<T>>) -> Self {
+        self.set_foreground(brush);
+        self
+    }
+
+    /// Set the foreground for this widget.
+    ///
+    /// This can be passed anything which can be represented by a [`BackgroundBrush`];
+    /// notably, it can be any [`Color`], a [`Key<Color>`] resolvable in the [`Env`],
+    /// any gradient, or a fully custom [`Painter`] widget.
+    ///
+    /// [`Key<Color>`]: crate::Key
+    /// [`Painter`]: super::Painter
+    pub fn set_foreground(&mut self, brush: impl Into<BackgroundBrush<T>>) {
+        self.foreground = Some(brush.into());
+    }
+
+    /// Clears foreground.
+    pub fn clear_foreground(&mut self) {
+        self.foreground = None;
+    }
+
     /// Builder-style method for painting a border around the widget with a color and width.
     ///
     /// Arguments can be either concrete values, or a [`Key`] of the respective
@@ -130,6 +162,11 @@ impl<T: Data> Container<T> {
         self.background.is_some()
     }
 
+    #[cfg(test)]
+    pub(crate) fn foreground_is_some(&self) -> bool {
+        self.foreground.is_some()
+    }
+
     #[cfg(test)]
     pub(crate) fn border_is_some(&self) -> bool {
         self.border.is_some()
@@ -158,6 +195,11 @@ impl<T: Data> Widget<T> for Container<T> {
                 brush.update(ctx, old_data, data, env);
             });
         }
+        if let Some(brush) = self.foreground.as_mut() {
+            trace_span!("update foreground").in_scope(|| {
+                brush.update(ctx, old_data, data, env);
+            });
+        }
         if let Some(border) = &self.border {
             if ctx.env_key_changed(&border.width) {
                 ctx.request_layout();
@@ -228,6 +270,17 @@ impl<T: Data> Widget<T> for Container<T> {
         };
 
         self.child.paint(ctx, data, env);
+
+        if let Some(foreground) = self.foreground.as_mut() {
+            let panel = ctx.size().to_rounded_rect(corner_radius);
+
+            trace_span!("paint foreground").in_scope(|| {
+                ctx.with_save(|ctx| {
+                    ctx.clip(panel);
+                    foreground.paint(ctx, data, env);
+                });
+            });
+        }
     }
 
     fn debug_state(&self, data: &T) -> DebugState {

druid/src/widget/widget_ext.rs

@@ -115,6 +115,13 @@ pub trait WidgetExt<T: Data>: Widget<T> + Sized + 'static {
         Container::new(self).background(brush)
     }
 
+    /// Wrap this widget in a [`Container`] with the provided foreground `brush`.
+    ///
+    /// See [`Container::foreground`] for more information.
+    fn foreground(self, brush: impl Into<BackgroundBrush<T>>) -> Container<T> {
+        Container::new(self).foreground(brush)
+    }
+
     /// Wrap this widget in a [`Container`] with the given border.
     ///
     /// Arguments can be either concrete values, or a [`Key`] of the respective
@@ -302,17 +309,21 @@ mod tests {
         // this should be Container<Align<Container<Slider>>>
         let widget = Slider::new()
             .background(Color::BLACK)
+            .foreground(Color::WHITE)
             .align_left()
             .border(Color::BLACK, 1.0);
         assert!(widget.border_is_some());
         assert!(!widget.background_is_some());
+        assert!(!widget.foreground_is_some());
 
         // this should be Container<Slider>
         let widget = Slider::new()
             .background(Color::BLACK)
-            .border(Color::BLACK, 1.0);
+            .border(Color::BLACK, 1.0)
+            .foreground(Color::WHITE);
         assert!(widget.background_is_some());
         assert!(widget.border_is_some());
+        assert!(widget.foreground_is_some());
     }
 
     #[test]