Add scrollable `Viewport`

2 files changed, 56 insertions, 47 deletions

diff --git a/native/src/widget/operation/scrollable.rs b/native/src/widget/operation/scrollable.rs
index 62f4c91e..f947344d 100644
--- a/native/src/widget/operation/scrollable.rs
+++ b/native/src/widget/operation/scrollable.rs
@@ -64,15 +64,6 @@ pub fn scroll_to<T>(target: Id, offset: AbsoluteOffset) -> impl Operation<T> {
     ScrollTo { target, offset }
 }
 
-/// The current absolute & relative offset of a [`Scrollable`]
-#[derive(Debug, Clone, Copy, PartialEq, Default)]
-pub struct CurrentOffset {
-    /// The [`AbsoluteOffset`] of a [`Scrollable`]
-    pub absolute: AbsoluteOffset,
-    /// The [`RelativeOffset`] of a [`Scrollable`]
-    pub relative: RelativeOffset,
-}
-
 /// The amount of absolute offset in each direction of a [`Scrollable`].
 #[derive(Debug, Clone, Copy, PartialEq, Default)]
 pub struct AbsoluteOffset {
diff --git a/native/src/widget/scrollable.rs b/native/src/widget/scrollable.rs
index eedddfd0..c66a166b 100644
--- a/native/src/widget/scrollable.rs
+++ b/native/src/widget/scrollable.rs
@@ -15,9 +15,7 @@ use crate::{
 };
 
 pub use iced_style::scrollable::StyleSheet;
-pub use operation::scrollable::{
-    AbsoluteOffset, CurrentOffset, RelativeOffset,
-};
+pub use operation::scrollable::{AbsoluteOffset, RelativeOffset};
 
 pub mod style {
     //! The styles of a [`Scrollable`].
@@ -40,7 +38,7 @@ where
     vertical: Properties,
     horizontal: Option<Properties>,
     content: Element<'a, Message, Renderer>,
-    on_scroll: Option<Box<dyn Fn(CurrentOffset) -> Message + 'a>>,
+    on_scroll: Option<Box<dyn Fn(Viewport) -> Message + 'a>>,
     style: <Renderer::Theme as StyleSheet>::Style,
 }
 
@@ -95,11 +93,8 @@ where
 
     /// Sets a function to call when the [`Scrollable`] is scrolled.
     ///
-    /// The function takes the [`CurrentOffset`] of the [`Scrollable`]
-    pub fn on_scroll(
-        mut self,
-        f: impl Fn(CurrentOffset) -> Message + 'a,
-    ) -> Self {
+    /// The function takes the [`Viewport`] of the [`Scrollable`]
+    pub fn on_scroll(mut self, f: impl Fn(Viewport) -> Message + 'a) -> Self {
         self.on_scroll = Some(Box::new(f));
         self
     }
@@ -437,7 +432,7 @@ pub fn update<Message>(
     shell: &mut Shell<'_, Message>,
     vertical: &Properties,
     horizontal: Option<&Properties>,
-    on_scroll: &Option<Box<dyn Fn(CurrentOffset) -> Message + '_>>,
+    on_scroll: &Option<Box<dyn Fn(Viewport) -> Message + '_>>,
     update_content: impl FnOnce(
         Event,
         Layout<'_>,
@@ -897,7 +892,7 @@ pub fn draw<Renderer>(
 
 fn notify_on_scroll<Message>(
     state: &mut State,
-    on_scroll: &Option<Box<dyn Fn(CurrentOffset) -> Message + '_>>,
+    on_scroll: &Option<Box<dyn Fn(Viewport) -> Message + '_>>,
     bounds: Rectangle,
     content_bounds: Rectangle,
     shell: &mut Shell<'_, Message>,
@@ -909,39 +904,29 @@ fn notify_on_scroll<Message>(
             return;
         }
 
-        let absolute_x =
-            state.offset_x.absolute(bounds.width, content_bounds.width);
-        let relative_x = absolute_x / (content_bounds.width - bounds.width);
-
-        let absolute_y = state
-            .offset_y
-            .absolute(bounds.height, content_bounds.height);
-        let relative_y = absolute_y / (content_bounds.height - bounds.height);
-
-        let absolute = AbsoluteOffset {
-            x: absolute_x,
-            y: absolute_y,
-        };
-        let relative = RelativeOffset {
-            x: relative_x,
-            y: relative_y,
+        let viewport = Viewport {
+            offset_x: state.offset_x,
+            offset_y: state.offset_y,
+            bounds,
+            content_bounds,
         };
 
-        // Don't publish redundant offsets to shell
-        if let Some(prev_relative) = state.last_notified {
+        // Don't publish redundant viewports to shell
+        if let Some(last_notified) = state.last_notified {
+            let prev = last_notified.relative_offset();
+            let curr = viewport.relative_offset();
+
             let unchanged = |a: f32, b: f32| {
                 (a - b).abs() <= f32::EPSILON || (a.is_nan() && b.is_nan())
             };
 
-            if unchanged(prev_relative.x, relative.x)
-                && unchanged(prev_relative.y, relative.y)
-            {
+            if unchanged(prev.x, curr.x) && unchanged(prev.y, curr.y) {
                 return;
             }
         }
 
-        shell.publish(on_scroll(CurrentOffset { absolute, relative }));
-        state.last_notified = Some(relative);
+        shell.publish(on_scroll(viewport));
+        state.last_notified = Some(viewport);
     }
 }
 
@@ -954,7 +939,7 @@ pub struct State {
     offset_x: Offset,
     x_scroller_grabbed_at: Option<f32>,
     keyboard_modifiers: keyboard::Modifiers,
-    last_notified: Option<RelativeOffset>,
+    last_notified: Option<Viewport>,
 }
 
 impl Default for State {
@@ -988,18 +973,51 @@ enum Offset {
 }
 
 impl Offset {
-    fn absolute(self, window: f32, content: f32) -> f32 {
+    fn absolute(self, viewport: f32, content: f32) -> f32 {
         match self {
             Offset::Absolute(absolute) => {
-                absolute.min((content - window).max(0.0))
+                absolute.min((content - viewport).max(0.0))
             }
             Offset::Relative(percentage) => {
-                ((content - window) * percentage).max(0.0)
+                ((content - viewport) * percentage).max(0.0)
             }
         }
     }
 }
 
+/// The current [`Viewport`] of the [`Scrollable`].
+#[derive(Debug, Clone, Copy)]
+pub struct Viewport {
+    offset_x: Offset,
+    offset_y: Offset,
+    bounds: Rectangle,
+    content_bounds: Rectangle,
+}
+
+impl Viewport {
+    /// Returns the [`AbsoluteOffset`] of the current [`Viewport`].
+    pub fn absolute_offset(&self) -> AbsoluteOffset {
+        let x = self
+            .offset_x
+            .absolute(self.bounds.width, self.content_bounds.width);
+        let y = self
+            .offset_y
+            .absolute(self.bounds.height, self.content_bounds.height);
+
+        AbsoluteOffset { x, y }
+    }
+
+    /// Returns the [`RelativeOffset`] of the current [`Viewport`].
+    pub fn relative_offset(&self) -> RelativeOffset {
+        let AbsoluteOffset { x, y } = self.absolute_offset();
+
+        let x = x / (self.content_bounds.width - self.bounds.width);
+        let y = y / (self.content_bounds.height - self.bounds.height);
+
+        RelativeOffset { x, y }
+    }
+}
+
 impl State {
     /// Creates a new [`State`] with the scrollbar(s) at the beginning.
     pub fn new() -> Self {