Add scroll_delta to FrameState

crates/egui/src/containers/scroll_area.rs

@@ -768,12 +768,12 @@ impl Prepared {
         for d in 0..2 {
             // We always take both scroll targets regardless of which scroll axes are enabled. This
             // is to avoid them leaking to other scroll areas.
-            let scroll_target = content_ui
-                .ctx()
-                .frame_state_mut(|state| state.scroll_target[d].take());
+            let (scroll_target, scroll_delta) = content_ui.ctx().frame_state_mut(|state| {
+                (state.scroll_target[d].take(), state.scroll_delta[d].take())
+            });
 
             if scroll_enabled[d] {
-                if let Some((target_range, align)) = scroll_target {
+                let mut delta = if let Some((target_range, align)) = scroll_target {
                     let min = content_ui.min_rect().min[d];
                     let clip_rect = content_ui.clip_rect();
                     let visible_range = min..=min + clip_rect.size()[d];
@@ -782,7 +782,7 @@ impl Prepared {
                     let clip_end = clip_rect.max[d];
                     let mut spacing = ui.spacing().item_spacing[d];
 
-                    let delta = if let Some(align) = align {
+                    if let Some(align) = align {
                         let center_factor = align.to_factor();
 
                         let offset =
@@ -799,29 +799,34 @@ impl Prepared {
                     } else {
                         // Ui is already in view, no need to adjust scroll.
                         0.0
-                    };
+                    }
+                } else {
+                    0.0
+                };
 
-                    if delta != 0.0 {
-                        let target_offset = state.offset[d] + delta;
+                if let Some(scroll_delta) = scroll_delta {
+                    delta += scroll_delta;
+                }
 
-                        if let Some(animation) = &mut state.offset_target[d] {
-                            // For instance: the user is continuously calling `ui.scroll_to_cursor`,
-                            // so we don't want to reset the animation, but perhaps update the target:
-                            animation.target_offset = target_offset;
-                        } else {
-                            // The further we scroll, the more time we take.
-                            // TODO(emilk): let users configure this in `Style`.
-                            let now = ui.input(|i| i.time);
-                            let points_per_second = 1000.0;
-                            let animation_duration =
-                                (delta.abs() / points_per_second).clamp(0.1, 0.3);
-                            state.offset_target[d] = Some(ScrollTarget {
-                                animation_time_span: (now, now + animation_duration as f64),
-                                target_offset,
-                            });
-                        }
-                        ui.ctx().request_repaint();
+                if delta != 0.0 {
+                    let target_offset = state.offset[d] + delta;
+
+                    if let Some(animation) = &mut state.offset_target[d] {
+                        // For instance: the user is continuously calling `ui.scroll_to_cursor`,
+                        // so we don't want to reset the animation, but perhaps update the target:
+                        animation.target_offset = target_offset;
+                    } else {
+                        // The further we scroll, the more time we take.
+                        // TODO(emilk): let users configure this in `Style`.
+                        let now = ui.input(|i| i.time);
+                        let points_per_second = 1000.0;
+                        let animation_duration = (delta.abs() / points_per_second).clamp(0.1, 0.3);
+                        state.offset_target[d] = Some(ScrollTarget {
+                            animation_time_span: (now, now + animation_duration as f64),
+                            target_offset,
+                        });
                     }
+                    ui.ctx().request_repaint();
                 }
             }
         }
@@ -851,8 +856,7 @@ impl Prepared {
 
         let max_offset = content_size - inner_rect.size();
         let is_hovering_outer_rect = ui.rect_contains_pointer(outer_rect);
-        let force_current_scroll_area = ui.input(|i| i.force_current_scroll_area);
-        if scrolling_enabled && is_hovering_outer_rect || force_current_scroll_area {
+        if scrolling_enabled && is_hovering_outer_rect {
             let always_scroll_enabled_direction = ui.style().always_scroll_the_only_direction
                 && scroll_enabled[0] != scroll_enabled[1];
             for d in 0..2 {
@@ -880,7 +884,6 @@ impl Prepared {
                             } else {
                                 input.smooth_scroll_delta[d] = 0.0;
                             }
-                            input.force_current_scroll_area = false;
                         });
 
                         state.scroll_stuck_to_end[d] = false;

crates/egui/src/frame_state.rs

@@ -38,9 +38,12 @@ pub(crate) struct FrameState {
     /// Initialized to `None` at the start of each frame.
     pub(crate) tooltip_state: Option<TooltipFrameState>,
 
-    /// horizontal, vertical
+    /// The current scroll area should scroll to this range (horizontal, vertical).
     pub(crate) scroll_target: [Option<(Rangef, Option<Align>)>; 2],
 
+    /// The current scroll area should scroll by this much (horizontal, vertical).
+    pub(crate) scroll_delta: [Option<f32>; 2],
+
     #[cfg(feature = "accesskit")]
     pub(crate) accesskit_state: Option<AccessKitFrameState>,
 
@@ -63,6 +66,7 @@ impl Default for FrameState {
             used_by_panels: Rect::NAN,
             tooltip_state: None,
             scroll_target: [None, None],
+            scroll_delta: [None, None],
             #[cfg(feature = "accesskit")]
             accesskit_state: None,
             highlight_this_frame: Default::default(),
@@ -84,6 +88,7 @@ impl FrameState {
             used_by_panels,
             tooltip_state,
             scroll_target,
+            scroll_delta,
             #[cfg(feature = "accesskit")]
             accesskit_state,
             highlight_this_frame,
@@ -99,6 +104,7 @@ impl FrameState {
         *used_by_panels = Rect::NOTHING;
         *tooltip_state = None;
         *scroll_target = [None, None];
+        *scroll_delta = [None, None];
 
         #[cfg(debug_assertions)]
         {

crates/egui/src/input_state.rs

@@ -70,10 +70,6 @@ pub struct InputState {
     /// at the end of the frame this will be zero if a scroll-area consumed the delta.
     pub smooth_scroll_delta: Vec2,
 
-    /// Force the current scroll area to consume the [Self::smooth_scroll_delta], independent of the focus / mouse position.
-    /// This is used when using [crate::Ui::scroll_with_delta] to scroll the current scroll area.
-    pub(crate) force_current_scroll_area: bool,
-
     /// Zoom scale factor this frame (e.g. from ctrl-scroll or pinch gesture).
     ///
     /// * `zoom = 1`: no change.
@@ -158,7 +154,6 @@ impl Default for InputState {
             unprocessed_scroll_delta: Vec2::ZERO,
             raw_scroll_delta: Vec2::ZERO,
             smooth_scroll_delta: Vec2::ZERO,
-            force_current_scroll_area: false,
             zoom_factor_delta: 1.0,
             screen_rect: Rect::from_min_size(Default::default(), vec2(10_000.0, 10_000.0)),
             pixels_per_point: 1.0,
@@ -260,7 +255,6 @@ impl InputState {
             unprocessed_scroll_delta,
             raw_scroll_delta,
             smooth_scroll_delta,
-            force_current_scroll_area: false,
             zoom_factor_delta,
             screen_rect,
             pixels_per_point,
@@ -1119,7 +1113,6 @@ impl InputState {
             unprocessed_scroll_delta,
             raw_scroll_delta,
             smooth_scroll_delta,
-            force_current_scroll_area,
 
             zoom_factor_delta,
             screen_rect,
@@ -1164,9 +1157,6 @@ impl InputState {
         ui.label(format!(
             "smooth_scroll_delta: {smooth_scroll_delta:?} points"
         ));
-        ui.label(format!(
-            "force_current_scroll_area: {force_current_scroll_area}"
-        ));
         ui.label(format!("zoom_factor_delta: {zoom_factor_delta:4.2}x"));
         ui.label(format!("screen_rect: {screen_rect:?} points"));
         ui.label(format!(

crates/egui/src/ui.rs

@@ -1091,9 +1091,8 @@ impl Ui {
     /// # });
     /// ```
     pub fn scroll_with_delta(&self, delta: Vec2) {
-        self.ctx().input_mut(|input| {
-            input.smooth_scroll_delta += delta;
-            input.force_current_scroll_area = true;
+        self.ctx().frame_state_mut(|state| {
+            state.scroll_delta = [Some(delta.x), Some(delta.y)];
         });
     }
 }

crates/egui_demo_lib/src/demo/scrolling.rs

@@ -294,7 +294,7 @@ impl super::View for ScrollTo {
             scroll_top |= ui.button("Scroll to top").clicked();
             scroll_bottom |= ui.button("Scroll to bottom").clicked();
             if ui.button("Scroll down by 64px").clicked() {
-                scroll_delta = Some(Vec2::new(0.0, -64.0));
+                scroll_delta = Some(Vec2::new(0.0, 64.0));
             }
         });