[style] Fade out windows on close

egui/src/containers/area.rs

@@ -158,6 +158,34 @@ impl Area {
         add_contents(&mut content_ui);
         prepared.end(ctx, content_ui)
     }
+
+    pub fn show_open_close_animation(&self, ctx: &CtxRef, frame: &Frame, is_open: bool) {
+        // must be called first so animation managers know the latest state
+        let visibility_factor = ctx.animate_bool(self.id.with("close_animation"), is_open);
+
+        if is_open {
+            // we actually only show close animations.
+            // when opening a window we show it right away.
+            return;
+        }
+        if visibility_factor <= 0.0 {
+            return;
+        }
+
+        let layer_id = LayerId::new(self.order, self.id);
+        let area_rect = ctx.memory().areas.get(self.id).map(|area| area.rect());
+        if let Some(area_rect) = area_rect {
+            let clip_rect = ctx.available_rect();
+            let painter = Painter::new(ctx.clone(), layer_id, clip_rect);
+
+            // shrinkage: looks kinda a bad on its own
+            // let area_rect =
+            //     Rect::from_center_size(area_rect.center(), visibility_factor * area_rect.size());
+
+            let frame = frame.multiply_with_opacity(visibility_factor);
+            painter.add(frame.paint(area_rect));
+        }
+    }
 }
 
 impl Prepared {

egui/src/containers/frame.rs

@@ -90,6 +90,13 @@ impl Frame {
         self.stroke = stroke;
         self
     }
+
+    pub fn multiply_with_opacity(mut self, opacity: f32) -> Self {
+        self.fill = self.fill.linear_multiply(opacity);
+        self.stroke.color = self.stroke.color.linear_multiply(opacity);
+        self.shadow.color = self.shadow.color.linear_multiply(opacity);
+        self
+    }
 }
 
 pub struct Prepared {
@@ -122,6 +129,31 @@ impl Frame {
         prepared.end(ui);
         ret
     }
+
+    pub fn paint(&self, outer_rect: Rect) -> Shape {
+        let Self {
+            margin: _,
+            corner_radius,
+            shadow,
+            fill,
+            stroke,
+        } = *self;
+
+        let frame_shape = Shape::Rect {
+            rect: outer_rect,
+            corner_radius,
+            fill,
+            stroke,
+        };
+
+        if shadow == Default::default() {
+            frame_shape
+        } else {
+            let shadow = shadow.tessellate(outer_rect, corner_radius);
+            let shadow = Shape::Triangles(shadow);
+            Shape::Vec(vec![shadow, frame_shape])
+        }
+    }
 }
 
 impl Prepared {
@@ -141,26 +173,9 @@ impl Prepared {
             ..
         } = self;
 
-        let frame_shape = Shape::Rect {
-            rect: outer_rect,
-            corner_radius: frame.corner_radius,
-            fill: frame.fill,
-            stroke: frame.stroke,
-        };
-
-        if frame.shadow == Default::default() {
-            ui.painter().set(where_to_put_background, frame_shape);
-        } else {
-            let shadow = frame.shadow.tessellate(outer_rect, frame.corner_radius);
-            let shadow = Shape::Triangles(shadow);
-            ui.painter().set(
-                where_to_put_background,
-                Shape::Vec(vec![shadow, frame_shape]),
-            )
-        };
-
+        let shape = frame.paint(outer_rect);
+        ui.painter().set(where_to_put_background, shape);
         ui.advance_cursor_after_rect(outer_rect);
-
         outer_rect
     }
 }

egui/src/containers/window.rs

@@ -224,7 +224,12 @@ impl<'open> Window<'open> {
             with_title_bar,
         } = self;
 
-        if matches!(open, Some(false)) && !ctx.memory().everything_is_visible() {
+        let frame = frame.unwrap_or_else(|| Frame::window(&ctx.style()));
+
+        let is_open = !matches!(open, Some(false)) || ctx.memory().everything_is_visible();
+        area.show_open_close_animation(ctx, &frame, is_open);
+
+        if !is_open {
             return None;
         }
 
@@ -244,8 +249,6 @@ impl<'open> Window<'open> {
         let resize = resize.resizable(false); // We move it manually
         let mut resize = resize.id(resize_id);
 
-        let frame = frame.unwrap_or_else(|| Frame::window(&ctx.style()));
-
         let mut area = area.begin(ctx);
 
         let title_content_spacing = 2.0 * ctx.style().spacing.item_spacing.y;

egui_demo_lib/src/apps/demo/widget_gallery.rs

@@ -22,7 +22,7 @@ impl Default for WidgetGallery {
             radio: Enum::First,
             scalar: 42.0,
             string: "Hello World!".to_owned(),
-            color: (egui::Rgba::from(egui::Color32::LIGHT_BLUE) * 0.5).into(),
+            color: egui::Color32::LIGHT_BLUE.linear_multiply(0.5),
         }
     }
 }

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)
 }
 
 // ----------------------------------------------------------------------------