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Scroll based on the mouse start position (#84)

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Fixes #57
This commit is contained in:
lucaspoffo 2021-01-02 12:41:20 -03:00 committed by GitHub
parent 8fd58dc827
commit 212fd80b01
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GPG key ID: 4AEE18F83AFDEB23
1 changed files with 22 additions and 10 deletions
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32
egui/src/containers/scroll_area.rs
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@ -12,6 +12,8 @@ pub(crate) struct State {
/// Momentum, used for kinetic scrolling
#[cfg_attr(feature = "serde", serde(skip))]
pub vel: Vec2,
/// Mouse offset relative to the top of the handle when started moving the handle.
scroll_start_offset_from_top: Option<f32>,
}
impl Default for State {
@ -20,6 +22,7 @@ impl Default for State {
offset: Vec2::zero(),
show_scroll: false,
vel: Vec2::zero(),
scroll_start_offset_from_top: None,
}
}
}
@ -282,17 +285,26 @@ impl Prepared {
if response.active {
if let Some(mouse_pos) = ui.input().mouse.pos {
if handle_rect.contains(mouse_pos) {
if inner_rect.top() <= mouse_pos.y && mouse_pos.y <= inner_rect.bottom() {
state.offset.y +=
ui.input().mouse.delta.y * content_size.y / inner_rect.height();
}
} else {
// Center scroll at mouse pos:
let mpos_top = mouse_pos.y - handle_rect.height() / 2.0;
state.offset.y = remap(mpos_top, top..=bottom, 0.0..=content_size.y);
}
let scroll_start_offset_from_top =
state.scroll_start_offset_from_top.get_or_insert_with(|| {
if handle_rect.contains(mouse_pos) {
mouse_pos.y - handle_rect.top()
} else {
let handle_top_pos_at_bottom = bottom - handle_rect.height();
// Calculate the new handle top position, centering the handle on the mouse.
let new_handle_top_pos = clamp(
mouse_pos.y - handle_rect.height() / 2.0,
top..=handle_top_pos_at_bottom,
);
mouse_pos.y - new_handle_top_pos
}
});
let new_handle_top = mouse_pos.y - *scroll_start_offset_from_top;
state.offset.y = remap(new_handle_top, top..=bottom, 0.0..=content_size.y);
}
} else {
state.scroll_start_offset_from_top = None;
}
state.offset.y = state.offset.y.max(0.0);