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Fix: Scroll doesn't work or is inaccurate in ScrollArea #5307

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Fix: Scroll doesn't work or is inaccurate in ScrollArea #5307

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32 changes: 22 additions & 10 deletions crates/egui/src/containers/scroll_area.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,9 @@ pub struct State {
/// If set, quickly but smoothly scroll to this target offset.
offset_target: [Option<ScrollingToTarget>; 2],

/// The offset value when the `offset_target` is set.
offset_target_start: [Option<f32>; 2],

/// Were the scroll bars visible last frame?
show_scroll: Vec2b,

Expand Down Expand Up @@ -52,6 +55,7 @@ impl Default for State {
Self {
offset: Vec2::ZERO,
offset_target: Default::default(),
offset_target_start: Default::default(),
show_scroll: Vec2b::FALSE,
content_is_too_large: Vec2b::FALSE,
scroll_bar_interaction: Vec2b::FALSE,
Expand Down Expand Up @@ -825,22 +829,25 @@ impl Prepared {

let content_size = content_ui.min_size();

let scroll_delta = content_ui
.ctx()
.pass_state_mut(|state| std::mem::take(&mut state.scroll_delta));

for d in 0..2 {
// PassState::scroll_delta is inverted from the way we apply the delta, so we need to negate it.
let mut delta = -scroll_delta.0[d];
let mut animation = scroll_delta.1;

// 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()
.pass_state_mut(|state| state.scroll_target[d].take());

if scroll_enabled[d] {
let (scroll_delta_0, scroll_delta_1) = content_ui.ctx().pass_state_mut(|state| {
(
std::mem::take(&mut state.scroll_delta.0[d]),
std::mem::take(&mut state.scroll_delta.1),
)
});

// PassState::scroll_delta is inverted from the way we apply the delta, so we need to negate it.
let mut delta = -scroll_delta_0;
let mut animation = scroll_delta_1;

if let Some(target) = scroll_target {
let pass_state::ScrollTarget {
range,
Expand Down Expand Up @@ -883,10 +890,14 @@ impl Prepared {

if !animated {
state.offset[d] = target_offset;
} else if let Some(animation) = &mut state.offset_target[d] {
} else if let Some(scroll_to_target) = &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;
if let Some(offset_target_start) = state.offset_target_start[d].take() {
let new_target_offset = offset_target_start + delta;
scroll_to_target.target_offset +=
scroll_to_target.target_offset - new_target_offset;
}
} else {
// The further we scroll, the more time we take.
let now = ui.input(|i| i.time);
Expand All @@ -896,6 +907,7 @@ impl Prepared {
animation_time_span: (now, now + animation_duration as f64),
target_offset,
});
state.offset_target_start[d] = Some(state.offset[d]);
}
ui.ctx().request_repaint();
}
Expand Down
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