Expose methods to change viewport alignment

widget/src/scrollable.rs

@@ -554,7 +554,14 @@ pub fn update<Message>(
 
  state.scroll(delta, direction, bounds, content_bounds);
 
- notify_on_scroll(state, on_scroll, bounds, content_bounds, shell);
+ notify_on_scroll(
+ state,
+ on_scroll,
+ bounds,
+ content_bounds,
+ direction,
+ shell,
+ );
 
  return event::Status::Captured;
  }
@@ -592,6 +599,7 @@ pub fn update<Message>(
  on_scroll,
  bounds,
  content_bounds,
+ direction,
  shell,
  );
  }
@@ -637,6 +645,7 @@ pub fn update<Message>(
  on_scroll,
  bounds,
  content_bounds,
+ direction,
  shell,
  );
 
@@ -672,6 +681,7 @@ pub fn update<Message>(
  on_scroll,
  bounds,
  content_bounds,
+ direction,
  shell,
  );
  }
@@ -712,6 +722,7 @@ pub fn update<Message>(
  on_scroll,
  bounds,
  content_bounds,
+ direction,
  shell,
  );
  }
@@ -747,6 +758,7 @@ pub fn update<Message>(
  on_scroll,
  bounds,
  content_bounds,
+ direction,
  shell,
  );
 
@@ -962,6 +974,7 @@ fn notify_on_scroll<Message>(
  on_scroll: &Option<Box<dyn Fn(Viewport) -> Message + '_>>,
  bounds: Rectangle,
  content_bounds: Rectangle,
+ direction: Direction,
  shell: &mut Shell<'_, Message>,
 ) {
  if let Some(on_scroll) = on_scroll {
@@ -971,11 +984,23 @@ fn notify_on_scroll<Message>(
  return;
  }
 
+ let horizontal_alignment = direction
+ .horizontal()
+ .map(|p| p.alignment)
+ .unwrap_or_default();
+
+ let vertical_alignment = direction
+ .vertical()
+ .map(|p| p.alignment)
+ .unwrap_or_default();
+
  let viewport = Viewport {
  offset_x: state.offset_x,
  offset_y: state.offset_y,
  bounds,
  content_bounds,
+ vertical_alignment,
+ horizontal_alignment,
  };
 
  // Don't publish redundant viewports to shell
@@ -1080,6 +1105,8 @@ pub struct Viewport {
  offset_y: Offset,
  bounds: Rectangle,
  content_bounds: Rectangle,
+ vertical_alignment: Alignment,
+ horizontal_alignment: Alignment,
 }
 
 impl Viewport {
@@ -1104,6 +1131,36 @@ impl Viewport {
 
  RelativeOffset { x, y }
  }
+
+ /// Returns a new [`Viewport`] with the supplied vertical [`Alignment`].
+ pub fn with_vertical_alignment(self, alignment: Alignment) -> Self {
+ if self.vertical_alignment != alignment {
+ let relative = 1.0 - self.relative_offset().y;
+
+ Self {
+ offset_y: Offset::Relative(relative),
+ vertical_alignment: alignment,
+ ..self
+ }
+ } else {
+ self
+ }
+ }
+
+ /// Returns a new [`Viewport`] with the supplied horizontal [`Alignment`].
+ pub fn with_horizontal_alignment(self, alignment: Alignment) -> Self {
+ if self.horizontal_alignment != alignment {
+ let relative = 1.0 - self.relative_offset().x;
+
+ Self {
+ offset_x: Offset::Relative(relative),
+ horizontal_alignment: alignment,
+ ..self
+ }
+ } else {
+ self
+ }
+ }
 }
 
 impl State {