Replace hard-coded params with struct members

graphics/src/widget/scrollable.rs

@@ -15,9 +15,6 @@ pub use iced_style::scrollable::{Scrollbar, Scroller, StyleSheet};
 pub type Scrollable<'a, Message, Backend> =
     iced_native::Scrollable<'a, Message, Renderer<Backend>>;
 
-const SCROLLBAR_WIDTH: u16 = 10;
-const SCROLLBAR_MARGIN: u16 = 2;
-
 impl<B> scrollable::Renderer for Renderer<B>
 where
     B: Backend,
@@ -29,13 +26,16 @@ where
         bounds: Rectangle,
         content_bounds: Rectangle,
         offset: u32,
+        scrollbar_width: u16,
+        scrollbar_margin: u16,
+        _scroller_width: u16,
     ) -> Option<scrollable::Scrollbar> {
         if content_bounds.height > bounds.height {
             let scrollbar_bounds = Rectangle {
                 x: bounds.x + bounds.width
-                    - f32::from(SCROLLBAR_WIDTH + 2 * SCROLLBAR_MARGIN),
+                    - f32::from(scrollbar_width + 2 * scrollbar_margin),
                 y: bounds.y,
-                width: f32::from(SCROLLBAR_WIDTH + 2 * SCROLLBAR_MARGIN),
+                width: f32::from(scrollbar_width + 2 * scrollbar_margin),
                 height: bounds.height,
             };
 
@@ -44,14 +44,15 @@ where
             let y_offset = offset as f32 * ratio;
 
             let scroller_bounds = Rectangle {
-                x: scrollbar_bounds.x + f32::from(SCROLLBAR_MARGIN),
+                x: scrollbar_bounds.x + f32::from(scrollbar_margin),
                 y: scrollbar_bounds.y + y_offset,
-                width: scrollbar_bounds.width - f32::from(2 * SCROLLBAR_MARGIN),
+                width: scrollbar_bounds.width - f32::from(2 * scrollbar_margin),
                 height: scrollbar_height,
             };
 
             Some(scrollable::Scrollbar {
                 bounds: scrollbar_bounds,
+                margin: scrollbar_margin,
                 scroller: scrollable::Scroller {
                     bounds: scroller_bounds,
                 },
@@ -110,9 +111,9 @@ where
                 let scrollbar = if is_scrollbar_visible {
                     Primitive::Quad {
                         bounds: Rectangle {
-                            x: scrollbar.bounds.x + f32::from(SCROLLBAR_MARGIN),
+                            x: scrollbar.bounds.x + f32::from(scrollbar.margin),
                             width: scrollbar.bounds.width
-                                - f32::from(2 * SCROLLBAR_MARGIN),
+                                - f32::from(2 * scrollbar.margin),
                             ..scrollbar.bounds
                         },
                         background: style

native/src/renderer/null.rs

@@ -89,6 +89,9 @@ impl scrollable::Renderer for Null {
         _bounds: Rectangle,
         _content_bounds: Rectangle,
         _offset: u32,
+        _scrollbar_width: u16,
+        _scrollbar_margin: u16,
+        _scroller_width: u16,
     ) -> Option<scrollable::Scrollbar> {
         None
     }

native/src/widget/scrollable.rs

@@ -13,6 +13,9 @@ pub struct Scrollable<'a, Message, Renderer: self::Renderer> {
     state: &'a mut State,
     height: Length,
     max_height: u32,
+    scrollbar_width: u16,
+    scrollbar_margin: u16,
+    scroller_width: u16,
     content: Column<'a, Message, Renderer>,
     style: Renderer::Style,
 }
@@ -27,6 +30,9 @@ impl<'a, Message, Renderer: self::Renderer> Scrollable<'a, Message, Renderer> {
             state,
             height: Length::Shrink,
             max_height: u32::MAX,
+            scrollbar_width: 10,
+            scrollbar_margin: 2,
+            scroller_width: 10,
             content: Column::new(),
             style: Renderer::Style::default(),
         }
@@ -90,6 +96,32 @@ impl<'a, Message, Renderer: self::Renderer> Scrollable<'a, Message, Renderer> {
         self
     }
 
+    /// Sets the scrollbar width of the [`Scrollable`] .
+    /// Silently enforces a minimum value of 1.
+    ///
+    /// [`Scrollable`]: struct.Scrollable.html
+    pub fn scrollbar_width(mut self, scrollbar_width: u16) -> Self {
+        self.scrollbar_width = scrollbar_width.max(1);
+        self
+    }
+
+    /// Sets the scrollbar margin of the [`Scrollable`] .
+    ///
+    /// [`Scrollable`]: struct.Scrollable.html
+    pub fn scrollbar_margin(mut self, scrollbar_margin: u16) -> Self {
+        self.scrollbar_margin = scrollbar_margin;
+        self
+    }
+
+    /// Sets the scroller width of the [`Scrollable`] .
+    /// Silently enforces a minimum value of 1.
+    ///
+    /// [`Scrollable`]: struct.Scrollable.html
+    pub fn scroller_width(mut self, scroller_width: u16) -> Self {
+        self.scroller_width = scroller_width.max(1);
+        self
+    }
+
     /// Sets the style of the [`Scrollable`] .
     ///
     /// [`Scrollable`]: struct.Scrollable.html
@@ -178,7 +210,14 @@ where
         }
 
         let offset = self.state.offset(bounds, content_bounds);
-        let scrollbar = renderer.scrollbar(bounds, content_bounds, offset);
+        let scrollbar = renderer.scrollbar(
+            bounds,
+            content_bounds,
+            offset,
+            self.scrollbar_width,
+            self.scrollbar_margin,
+            self.scroller_width,
+        );
         let is_mouse_over_scrollbar = scrollbar
             .as_ref()
             .map(|scrollbar| scrollbar.is_mouse_over(cursor_position))
@@ -269,7 +308,14 @@ where
         let content_layout = layout.children().next().unwrap();
         let content_bounds = content_layout.bounds();
         let offset = self.state.offset(bounds, content_bounds);
-        let scrollbar = renderer.scrollbar(bounds, content_bounds, offset);
+        let scrollbar = renderer.scrollbar(
+            bounds,
+            content_bounds,
+            offset,
+            self.scrollbar_width,
+            self.scrollbar_margin,
+            self.scroller_width,
+        );
 
         let is_mouse_over = bounds.contains(cursor_position);
         let is_mouse_over_scrollbar = scrollbar
@@ -418,6 +464,11 @@ pub struct Scrollbar {
     /// [`Scrollbar`]: struct.Scrollbar.html
     pub bounds: Rectangle,
 
+    /// The margin within the [`Scrollbar`].
+    ///
+    /// [`Scrollbar`]: struct.Scrollbar.html
+    pub margin: u16,
+
     /// The bounds of the [`Scroller`].
     ///
     /// [`Scroller`]: struct.Scroller.html
@@ -486,6 +537,9 @@ pub trait Renderer: column::Renderer + Sized {
         bounds: Rectangle,
         content_bounds: Rectangle,
         offset: u32,
+        scrollbar_width: u16,
+        scrollbar_margin: u16,
+        scroller_width: u16,
     ) -> Option<Scrollbar>;
 
     /// Draws the [`Scrollable`].