ScrollArea override_scroll_delta()

crates/egui/src/containers/scroll_area.rs

@@ -106,6 +106,9 @@ pub struct ScrollArea {
     /// end position until user manually changes position. It will become true
     /// again once scroll handle makes contact with end.
     stick_to_end: [bool; 2],
+
+    /// Override for scroll delta. Normally taken from frame_state
+    override_scroll_delta: Option<Vec2>,
 }
 
 impl ScrollArea {
@@ -145,9 +148,11 @@ impl ScrollArea {
             scrolling_enabled: true,
             drag_to_scroll: true,
             stick_to_end: [false; 2],
+            override_scroll_delta: None,
         }
     }
 
+
     /// The maximum width of the outer frame of the scroll area.
     ///
     /// Use `f32::INFINITY` if you want the scroll area to expand to fit the surrounding [`Ui`] (default).
@@ -318,6 +323,11 @@ impl ScrollArea {
         self.stick_to_end[1] = stick;
         self
     }
+
+    pub fn override_scroll_delta(mut self, delta: Vec2) -> Self {
+        self.override_scroll_delta = Some(delta);
+        self
+    }
 }
 
 struct Prepared {
@@ -337,6 +347,7 @@ struct Prepared {
     viewport: Rect,
     scrolling_enabled: bool,
     stick_to_end: [bool; 2],
+    override_scroll_delta: Option<Vec2>,
 }
 
 impl ScrollArea {
@@ -353,6 +364,7 @@ impl ScrollArea {
             scrolling_enabled,
             drag_to_scroll,
             stick_to_end,
+            override_scroll_delta,
         } = self;
 
         let ctx = ui.ctx().clone();
@@ -507,6 +519,7 @@ impl ScrollArea {
             viewport,
             scrolling_enabled,
             stick_to_end,
+            override_scroll_delta,
         }
     }
 
@@ -617,6 +630,7 @@ impl Prepared {
             viewport: _,
             scrolling_enabled,
             stick_to_end,
+            override_scroll_delta,
         } = self;
 
         let content_size = content_ui.min_size();
@@ -691,7 +705,10 @@ impl Prepared {
         if scrolling_enabled && ui.rect_contains_pointer(outer_rect) {
             for d in 0..2 {
                 if has_bar[d] {
-                    let scroll_delta = ui.ctx().frame_state(|fs| fs.scroll_delta);
+                    let scroll_delta = match override_scroll_delta {
+                        Some(delta) => delta,
+                        None => ui.ctx().frame_state(|fs| fs.scroll_delta)
+                    };
 
                     let scrolling_up = state.offset[d] > 0.0 && scroll_delta[d] > 0.0;
                     let scrolling_down = state.offset[d] < max_offset[d] && scroll_delta[d] < 0.0;