feat: enhance PlainSlider to eliminate visual artifacts and improve boundary handling

hcie-iced-app/crates/hcie-iced-gui/src/widgets/plain_slider.rs

@@ -110,6 +110,25 @@ impl<Message> PlainSlider<Message> {
         self.snap(*self.range.start() + (*self.range.end() - *self.range.start()) * fraction)
     }
 
+    /// Computes the slider value for the current cursor position while dragging.
+    ///
+    /// **Purpose:** Allow an active drag to continue updating even when the cursor moves
+    /// slightly outside the widget bounds, so 0 % and 100 % can always be reached.
+    /// **Logic & Workflow:** If the cursor is inside the widget bounds, use its local X.
+    /// Otherwise fall back to the global cursor position and convert it to widget-local
+    /// X by subtracting `bounds.x`. Clamp the resulting X to the draggable track width.
+    /// **Arguments:** `cursor` is the current mouse cursor; `bounds` is the widget rectangle.
+    /// **Returns:** The stepped value at the clamped cursor position.
+    fn drag_value(&self, cursor: mouse::Cursor, bounds: Rectangle) -> f32 {
+        let track_width = (bounds.width - SPINNER_WIDTH).max(1.0);
+        let x = match cursor.position_in(bounds) {
+            Some(local) => local.x,
+            None => cursor.position().map_or(0.0, |p| p.x - bounds.x),
+        }
+        .clamp(0.0, track_width);
+        self.value_at(x, bounds.width)
+    }
+
     /// Returns the normalized fill fraction for the current value.
     fn fraction(&self) -> f32 {
         let span = *self.range.end() - *self.range.start();
@@ -170,22 +189,10 @@ impl<Message> canvas::Program<Message> for PlainSlider<Message> {
         let track_width = (bounds.width - SPINNER_WIDTH).max(0.0);
         let fill_width = track_width * self.fraction();
         if fill_width > 0.0 {
-            let bands = 4;
-            for band in 0..bands {
-                let t = band as f32 / (bands - 1) as f32;
-                let mut fill = mix_color(self.colors.accent, self.colors.accent_hover, t * 0.55);
-                fill.a = if self.colors.is_light { 0.30 } else { 0.25 };
-                frame.fill_rectangle(
-                    Point::new(0.0, bounds.height * band as f32 / bands as f32),
-                    Size::new(fill_width, bounds.height / bands as f32 + 0.5),
-                    fill,
-                );
-            }
-            frame.fill_rectangle(
-                Point::new((fill_width - 1.5).max(0.0), 1.0),
-                Size::new(3.0_f32.min(fill_width), (bounds.height - 2.0).max(0.0)),
-                self.colors.accent,
-            );
+            let mut fill = self.colors.accent;
+            fill.a = if self.colors.is_light { 0.30 } else { 0.25 };
+            let fill_rect = Path::rounded_rectangle(Point::new(0.0, 0.0), Size::new(fill_width, bounds.height), radius);
+            frame.fill(&fill_rect, fill);
         }
 
         frame.stroke(
@@ -298,14 +305,11 @@ impl<Message> canvas::Program<Message> for PlainSlider<Message> {
                 (canvas::event::Status::Ignored, None)
             }
             canvas::Event::Mouse(mouse::Event::CursorMoved { .. }) if state.dragging => {
-                if let Some(position) = local {
-                    let value = self.value_at(position.x, bounds.width);
-                    return (
-                        canvas::event::Status::Captured,
-                        Some((self.on_change)(value)),
-                    );
-                }
-                (canvas::event::Status::Captured, None)
+                let value = self.drag_value(cursor, bounds);
+                return (
+                    canvas::event::Status::Captured,
+                    Some((self.on_change)(value)),
+                );
             }
             canvas::Event::Mouse(mouse::Event::ButtonReleased(mouse::Button::Left)) => {
                 if state.dragging {
@@ -409,17 +413,6 @@ fn is_numeric_fragment(text: &str) -> bool {
             .all(|character| character.is_ascii_digit() || matches!(character, '.' | ',' | '-'))
 }
 
-/// Blends two theme colors while preserving alpha interpolation.
-fn mix_color(from: iced::Color, to: iced::Color, amount: f32) -> iced::Color {
-    let amount = amount.clamp(0.0, 1.0);
-    iced::Color::new(
-        from.r + (to.r - from.r) * amount,
-        from.g + (to.g - from.g) * amount,
-        from.b + (to.b - from.b) * amount,
-        from.a + (to.a - from.a) * amount,
-    )
-}
-
 #[cfg(test)]
 mod tests {
     use super::{is_numeric_fragment, PlainSlider, State};
@@ -463,4 +456,11 @@ mod tests {
         assert_eq!(slider.value_at(100.0, 124.0), 1.0);
         assert!((slider.value_at(33.0, 124.0) - 0.33).abs() < 1e-6);
     }
+
+    #[test]
+    fn pointer_mapping_clamps_outside_track() {
+        let slider = test_slider("");
+        assert_eq!(slider.value_at(-10.0, 124.0), 0.0);
+        assert_eq!(slider.value_at(120.0, 124.0), 1.0);
+    }
 }