Improve tessellation quality

crates/ecolor/src/color32.rs

@@ -72,6 +72,8 @@ impl Color32 {
     pub const BLUE: Self = Self::from_rgb(0, 0, 255);
     pub const LIGHT_BLUE: Self = Self::from_rgb(0xAD, 0xD8, 0xE6);
 
+    pub const PURPLE: Self = Self::from_rgb(0x80, 0, 0x80);
+
     pub const GOLD: Self = Self::from_rgb(255, 215, 0);
 
     pub const DEBUG_COLOR: Self = Self::from_rgba_premultiplied(0, 200, 0, 128);
@@ -233,6 +235,23 @@ impl Color32 {
         ])
     }
 
+    /// Multiply with 127 to make color half as opaque, perceptually.
+    ///
+    /// Fast multiplication in gamma-space.
+    ///
+    /// This is perceptually even, and faster that [`Self::linear_multiply`].
+    #[inline]
+    pub fn gamma_multiply_u8(self, factor: u8) -> Self {
+        let Self([r, g, b, a]) = self;
+        let factor = factor as u32;
+        Self([
+            ((r as u32 * factor + 127) / 255) as u8,
+            ((g as u32 * factor + 127) / 255) as u8,
+            ((b as u32 * factor + 127) / 255) as u8,
+            ((a as u32 * factor + 127) / 255) as u8,
+        ])
+    }
+
     /// Multiply with 0.5 to make color half as opaque in linear space.
     ///
     /// This is using linear space, which is not perceptually even.
@@ -271,6 +290,11 @@ impl Color32 {
             fast_round(lerp((self[3] as f32)..=(other[3] as f32), t)),
         )
     }
+
+    /// Blend two colors, so that `self` is behind the argument.
+    pub fn blend(self, on_top: Self) -> Self {
+        self.gamma_multiply_u8(255 - on_top.a()) + on_top
+    }
 }
 
 impl std::ops::Mul for Color32 {
@@ -287,3 +311,17 @@ impl std::ops::Mul for Color32 {
         ])
     }
 }
+
+impl std::ops::Add for Color32 {
+    type Output = Self;
+
+    #[inline]
+    fn add(self, other: Self) -> Self {
+        Self([
+            self[0].saturating_add(other[0]),
+            self[1].saturating_add(other[1]),
+            self[2].saturating_add(other[2]),
+            self[3].saturating_add(other[3]),
+        ])
+    }
+}

crates/egui/src/containers/frame.rs

@@ -115,7 +115,10 @@ pub struct Frame {
     #[doc(alias = "border")]
     pub stroke: Stroke,
 
-    /// The rounding of the corners of [`Self::stroke`] and [`Self::fill`].
+    /// The rounding of the _outer_ corner of the [`Self::stroke`]
+    /// (or, if there is no stroke, the outer corner of [`Self::fill`]).
+    ///
+    /// In other words, this is the corner radius of the _widget rect_.
     pub rounding: Rounding,
 
     /// Margin outside the painted frame.
@@ -269,7 +272,10 @@ impl Frame {
         self
     }
 
-    /// The rounding of the corners of [`Self::stroke`] and [`Self::fill`].
+    /// The rounding of the _outer_ corner of the [`Self::stroke`]
+    /// (or, if there is no stroke, the outer corner of [`Self::fill`]).
+    ///
+    /// In other words, this is the corner radius of the _widget rect_.
     #[inline]
     pub fn rounding(mut self, rounding: impl Into<Rounding>) -> Self {
         self.rounding = rounding.into();
@@ -423,15 +429,14 @@ impl Frame {
             shadow,
         } = *self;
 
-        let fill_rect = self.fill_rect(content_rect);
         let widget_rect = self.widget_rect(content_rect);
 
         let frame_shape = Shape::Rect(epaint::RectShape::new(
-            fill_rect,
+            widget_rect,
             rounding,
             fill,
             stroke,
-            epaint::StrokeKind::Outside,
+            epaint::StrokeKind::Inside,
         ));
 
         if shadow == Default::default() {

crates/egui/src/containers/window.rs

@@ -611,7 +611,8 @@ impl Window<'_> {
                         title_bar.inner_rect.round_to_pixels(ctx.pixels_per_point());
 
                     if on_top && area_content_ui.visuals().window_highlight_topmost {
-                        let mut round = window_frame.rounding;
+                        let mut round =
+                            window_frame.rounding - window_frame.stroke.width.round() as u8;
 
                         if !is_collapsed {
                             round.se = 0;

crates/egui/src/introspection.rs

@@ -160,7 +160,7 @@ impl Widget for &mut epaint::TessellationOptions {
                     .on_hover_text("Apply feathering to smooth out the edges of shapes. Turn off for small performance gain.");
 
                 if *feathering {
-                    ui.add(crate::DragValue::new(feathering_size_in_pixels).range(0.0..=10.0).speed(0.1).suffix(" px"));
+                    ui.add(crate::DragValue::new(feathering_size_in_pixels).range(0.0..=10.0).speed(0.025).suffix(" px"));
                 }
             });
 

crates/egui_demo_lib/src/demo/demo_app_windows.rs

@@ -100,6 +100,7 @@ impl Default for DemoGroups {
                 Box::<super::tests::InputTest>::default(),
                 Box::<super::tests::LayoutTest>::default(),
                 Box::<super::tests::ManualLayoutTest>::default(),
+                Box::<super::tests::TessellationTest>::default(),
                 Box::<super::tests::WindowResizeTest>::default(),
             ]),
         }

crates/egui_demo_lib/src/demo/misc_demo_window.rs

@@ -124,9 +124,9 @@ impl View for MiscDemoWindow {
                     )
                     .changed()
                 {
-                    self.checklist
-                        .iter_mut()
-                        .for_each(|checked| *checked = all_checked);
+                    for check in &mut self.checklist {
+                        *check = all_checked;
+                    }
                 }
                 for (i, checked) in self.checklist.iter_mut().enumerate() {
                     ui.checkbox(checked, format!("Item {}", i + 1));

crates/egui_demo_lib/src/demo/tests/mod.rs

@@ -6,6 +6,7 @@ mod input_event_history;
 mod input_test;
 mod layout_test;
 mod manual_layout_test;
+mod tessellation_test;
 mod window_resize_test;
 
 pub use clipboard_test::ClipboardTest;
@@ -16,4 +17,5 @@ pub use input_event_history::InputEventHistory;
 pub use input_test::InputTest;
 pub use layout_test::LayoutTest;
 pub use manual_layout_test::ManualLayoutTest;
+pub use tessellation_test::TessellationTest;
 pub use window_resize_test::WindowResizeTest;