use std::cmp::Ordering;
use crate::{ScrollAxes, ScrollState, UiNodeId, UiPoint, UiRect, UiSize};
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum ScrollAxis {
Horizontal,
Vertical,
}
impl ScrollAxis {
pub const fn value(self, point: UiPoint) -> f32 {
match self {
Self::Horizontal => point.x,
Self::Vertical => point.y,
}
}
pub const fn size_value(self, size: UiSize) -> f32 {
match self {
Self::Horizontal => size.width,
Self::Vertical => size.height,
}
}
pub const fn rect_start(self, rect: UiRect) -> f32 {
match self {
Self::Horizontal => rect.x,
Self::Vertical => rect.y,
}
}
pub fn rect_end(self, rect: UiRect) -> f32 {
match self {
Self::Horizontal => rect.right(),
Self::Vertical => rect.bottom(),
}
}
pub const fn with_value(self, point: UiPoint, value: f32) -> UiPoint {
match self {
Self::Horizontal => UiPoint::new(value, point.y),
Self::Vertical => UiPoint::new(point.x, value),
}
}
pub const fn enabled_by(self, axes: ScrollAxes) -> bool {
match self {
Self::Horizontal => axes.horizontal,
Self::Vertical => axes.vertical,
}
}
}
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct ScrollInsets {
pub top: f32,
pub right: f32,
pub bottom: f32,
pub left: f32,
}
impl ScrollInsets {
pub const ZERO: Self = Self::uniform(0.0);
pub const fn uniform(value: f32) -> Self {
Self {
top: value,
right: value,
bottom: value,
left: value,
}
}
pub const fn new(top: f32, right: f32, bottom: f32, left: f32) -> Self {
Self {
top,
right,
bottom,
left,
}
}
pub fn expand_rect(self, rect: UiRect) -> UiRect {
UiRect::new(
rect.x - self.left.max(0.0),
rect.y - self.top.max(0.0),
rect.width + self.left.max(0.0) + self.right.max(0.0),
rect.height + self.top.max(0.0) + self.bottom.max(0.0),
)
}
}
impl Default for ScrollInsets {
fn default() -> Self {
Self::ZERO
}
}
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum OverscrollBehavior {
Auto,
Contain,
None,
}
impl OverscrollBehavior {
pub const fn allows_chain(self) -> bool {
matches!(self, Self::Auto)
}
}
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub struct OverscrollPolicy {
pub horizontal: OverscrollBehavior,
pub vertical: OverscrollBehavior,
}
impl OverscrollPolicy {
pub const AUTO: Self = Self {
horizontal: OverscrollBehavior::Auto,
vertical: OverscrollBehavior::Auto,
};
pub const CONTAIN: Self = Self {
horizontal: OverscrollBehavior::Contain,
vertical: OverscrollBehavior::Contain,
};
pub const NONE: Self = Self {
horizontal: OverscrollBehavior::None,
vertical: OverscrollBehavior::None,
};
pub const fn new(horizontal: OverscrollBehavior, vertical: OverscrollBehavior) -> Self {
Self {
horizontal,
vertical,
}
}
pub const fn behavior(self, axis: ScrollAxis) -> OverscrollBehavior {
match axis {
ScrollAxis::Horizontal => self.horizontal,
ScrollAxis::Vertical => self.vertical,
}
}
}
impl Default for OverscrollPolicy {
fn default() -> Self {
Self::AUTO
}
}
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct ScrollDeltaResolution {
pub offset_before: UiPoint,
pub offset_after: UiPoint,
pub consumed_delta: UiPoint,
pub overscroll_delta: UiPoint,
}
pub fn resolve_scroll_delta(state: ScrollState, delta: UiPoint) -> ScrollDeltaResolution {
let delta = finite_point(delta);
let offset_before = finite_point(state.offset);
let max_offset = state.max_offset();
let desired = UiPoint::new(
if state.axes.horizontal {
offset_before.x + delta.x
} else {
offset_before.x
},
if state.axes.vertical {
offset_before.y + delta.y
} else {
offset_before.y
},
);
let offset_after = UiPoint::new(
clamp_axis(desired.x, 0.0, max_offset.x),
clamp_axis(desired.y, 0.0, max_offset.y),
);
let consumed_delta = UiPoint::new(
offset_after.x - offset_before.x,
offset_after.y - offset_before.y,
);
ScrollDeltaResolution {
offset_before,
offset_after,
consumed_delta,
overscroll_delta: UiPoint::new(delta.x - consumed_delta.x, delta.y - consumed_delta.y),
}
}
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct NestedScrollCandidate {
pub node: UiNodeId,
pub state: ScrollState,
pub overscroll: OverscrollPolicy,
}
impl NestedScrollCandidate {
pub const fn new(node: UiNodeId, state: ScrollState) -> Self {
Self {
node,
state,
overscroll: OverscrollPolicy::AUTO,
}
}
pub const fn overscroll(mut self, overscroll: OverscrollPolicy) -> Self {
self.overscroll = overscroll;
self
}
}
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct NestedScrollStep {
pub node: UiNodeId,
pub input_delta: UiPoint,
pub consumed_delta: UiPoint,
pub overscroll_delta: UiPoint,
pub offset_before: UiPoint,
pub offset_after: UiPoint,
}
#[derive(Debug, Clone, PartialEq)]
pub struct NestedScrollPlan {
pub steps: Vec<NestedScrollStep>,
pub remaining_delta: UiPoint,
pub blocked_delta: UiPoint,
}
impl NestedScrollPlan {
pub fn changed_nodes(&self) -> Vec<UiNodeId> {
self.steps
.iter()
.filter(|step| point_has_delta(step.consumed_delta))
.map(|step| step.node)
.collect()
}
pub fn offset_after(&self, node: UiNodeId) -> Option<UiPoint> {
self.steps
.iter()
.find(|step| step.node == node)
.map(|step| step.offset_after)
}
}
pub fn arbitrate_nested_scroll(
delta: UiPoint,
candidates: &[NestedScrollCandidate],
) -> NestedScrollPlan {
let mut remaining_delta = finite_point(delta);
let mut blocked_delta = UiPoint::new(0.0, 0.0);
let mut steps = Vec::new();
for candidate in candidates {
if !point_has_delta(remaining_delta) {
break;
}
let resolution = resolve_scroll_delta(candidate.state, remaining_delta);
let mut chained_delta = UiPoint::new(0.0, 0.0);
let mut locally_blocked = UiPoint::new(0.0, 0.0);
for axis in [ScrollAxis::Horizontal, ScrollAxis::Vertical] {
let overscroll = axis.value(resolution.overscroll_delta);
if overscroll.abs() <= f32::EPSILON {
continue;
}
if candidate.overscroll.behavior(axis).allows_chain() {
chained_delta = axis.with_value(chained_delta, overscroll);
} else {
locally_blocked = axis.with_value(locally_blocked, overscroll);
}
}
blocked_delta = UiPoint::new(
blocked_delta.x + locally_blocked.x,
blocked_delta.y + locally_blocked.y,
);
steps.push(NestedScrollStep {
node: candidate.node,
input_delta: remaining_delta,
consumed_delta: resolution.consumed_delta,
overscroll_delta: resolution.overscroll_delta,
offset_before: resolution.offset_before,
offset_after: resolution.offset_after,
});
remaining_delta = chained_delta;
}
NestedScrollPlan {
steps,
remaining_delta,
blocked_delta,
}
}
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum RevealAlignment {
Nearest,
Start,
Center,
End,
}
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum ProgrammaticScrollBehavior {
Instant,
Smooth { duration_ms: u32 },
}
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct RevealOptions {
pub inline: RevealAlignment,
pub block: RevealAlignment,
pub margin: ScrollInsets,
pub behavior: ProgrammaticScrollBehavior,
}
impl RevealOptions {
pub const fn nearest() -> Self {
Self {
inline: RevealAlignment::Nearest,
block: RevealAlignment::Nearest,
margin: ScrollInsets::ZERO,
behavior: ProgrammaticScrollBehavior::Instant,
}
}
pub const fn align(inline: RevealAlignment, block: RevealAlignment) -> Self {
Self {
inline,
block,
margin: ScrollInsets::ZERO,
behavior: ProgrammaticScrollBehavior::Instant,
}
}
pub const fn margin(mut self, margin: ScrollInsets) -> Self {
self.margin = margin;
self
}
pub const fn behavior(mut self, behavior: ProgrammaticScrollBehavior) -> Self {
self.behavior = behavior;
self
}
}
impl Default for RevealOptions {
fn default() -> Self {
Self::nearest()
}
}
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct RevealScrollPlan {
pub offset_before: UiPoint,
pub offset_after: UiPoint,
pub delta: UiPoint,
pub behavior: ProgrammaticScrollBehavior,
}
impl RevealScrollPlan {
pub fn changed(self) -> bool {
point_has_delta(self.delta)
}
}
pub fn reveal_rect_into_view(
scroll: ScrollState,
target_rect: UiRect,
options: RevealOptions,
) -> RevealScrollPlan {
let target = options.margin.expand_rect(target_rect);
let max = scroll.max_offset();
let mut offset = finite_point(scroll.offset);
if scroll.axes.horizontal {
offset.x = reveal_axis_offset(
offset.x,
scroll.viewport_size.width,
max.x,
target.x,
target.right(),
options.inline,
);
}
if scroll.axes.vertical {
offset.y = reveal_axis_offset(
offset.y,
scroll.viewport_size.height,
max.y,
target.y,
target.bottom(),
options.block,
);
}
let offset_after = UiPoint::new(
clamp_axis(offset.x, 0.0, max.x),
clamp_axis(offset.y, 0.0, max.y),
);
let offset_before = finite_point(scroll.offset);
RevealScrollPlan {
offset_before,
offset_after,
delta: UiPoint::new(
offset_after.x - offset_before.x,
offset_after.y - offset_before.y,
),
behavior: options.behavior,
}
}
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct ScrollAnchorCandidate {
pub node: UiNodeId,
pub rect_before: UiRect,
pub rect_after: UiRect,
pub priority: i32,
pub order: usize,
pub enabled: bool,
}
impl ScrollAnchorCandidate {
pub const fn new(node: UiNodeId, rect_before: UiRect, rect_after: UiRect) -> Self {
Self {
node,
rect_before,
rect_after,
priority: 0,
order: 0,
enabled: true,
}
}
pub const fn priority(mut self, priority: i32) -> Self {
self.priority = priority;
self
}
pub const fn order(mut self, order: usize) -> Self {
self.order = order;
self
}
pub const fn enabled(mut self, enabled: bool) -> Self {
self.enabled = enabled;
self
}
}
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct ScrollAnchorAdjustment {
pub anchor: Option<UiNodeId>,
pub offset_before: UiPoint,
pub offset_after: UiPoint,
pub delta: UiPoint,
}
pub fn apply_scroll_anchor(
scroll: ScrollState,
candidates: &[ScrollAnchorCandidate],
) -> ScrollAnchorAdjustment {
let offset_before = finite_point(scroll.offset);
let Some(anchor) = select_scroll_anchor(scroll, candidates) else {
return ScrollAnchorAdjustment {
anchor: None,
offset_before,
offset_after: offset_before,
delta: UiPoint::new(0.0, 0.0),
};
};
let mut delta = UiPoint::new(0.0, 0.0);
if scroll.axes.horizontal {
delta.x = anchor.rect_after.x - anchor.rect_before.x;
}
if scroll.axes.vertical {
delta.y = anchor.rect_after.y - anchor.rect_before.y;
}
let max = scroll.max_offset();
let offset_after = UiPoint::new(
clamp_axis(offset_before.x + delta.x, 0.0, max.x),
clamp_axis(offset_before.y + delta.y, 0.0, max.y),
);
ScrollAnchorAdjustment {
anchor: Some(anchor.node),
offset_before,
offset_after,
delta: UiPoint::new(
offset_after.x - offset_before.x,
offset_after.y - offset_before.y,
),
}
}
pub fn select_scroll_anchor<'a>(
scroll: ScrollState,
candidates: &'a [ScrollAnchorCandidate],
) -> Option<&'a ScrollAnchorCandidate> {
let viewport = content_viewport_rect(scroll);
candidates
.iter()
.filter(|candidate| candidate.enabled)
.filter_map(|candidate| {
let visible_area = candidate
.rect_before
.intersection(viewport)
.map(rect_area)
.unwrap_or(0.0);
(visible_area > f32::EPSILON).then_some((candidate, visible_area))
})
.max_by(|left, right| compare_anchor_candidate(*left, *right))
.map(|(candidate, _)| candidate)
}
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct StickyEdges {
pub top: Option<f32>,
pub right: Option<f32>,
pub bottom: Option<f32>,
pub left: Option<f32>,
}
impl StickyEdges {
pub const NONE: Self = Self {
top: None,
right: None,
bottom: None,
left: None,
};
pub const fn top(value: f32) -> Self {
Self {
top: Some(value),
right: None,
bottom: None,
left: None,
}
}
pub const fn left(value: f32) -> Self {
Self {
top: None,
right: None,
bottom: None,
left: Some(value),
}
}
}
impl Default for StickyEdges {
fn default() -> Self {
Self::NONE
}
}
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct StickyConstraints {
pub scrollport: UiRect,
pub containing_block: UiRect,
pub edges: StickyEdges,
}
impl StickyConstraints {
pub const fn new(scrollport: UiRect, containing_block: UiRect, edges: StickyEdges) -> Self {
Self {
scrollport,
containing_block,
edges,
}
}
}
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct FixedConstraints {
pub viewport: UiRect,
pub viewport_rect: UiRect,
}
impl FixedConstraints {
pub const fn new(viewport: UiRect, viewport_rect: UiRect) -> Self {
Self {
viewport,
viewport_rect,
}
}
}
#[derive(Debug, Clone, Copy, PartialEq)]
pub enum ScrollAttachment {
Flow,
Sticky(StickyConstraints),
Fixed(FixedConstraints),
}
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum ScrollAttachmentMode {
Flow,
Stuck,
Fixed,
}
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct ScrollAttachmentResolution {
pub mode: ScrollAttachmentMode,
pub rect: UiRect,
pub delta: UiPoint,
}
pub fn resolve_scroll_attachment(
normal_rect: UiRect,
attachment: ScrollAttachment,
) -> ScrollAttachmentResolution {
match attachment {
ScrollAttachment::Flow => ScrollAttachmentResolution {
mode: ScrollAttachmentMode::Flow,
rect: normal_rect,
delta: UiPoint::new(0.0, 0.0),
},
ScrollAttachment::Sticky(constraints) => resolve_sticky_rect(normal_rect, constraints),
ScrollAttachment::Fixed(constraints) => {
let rect = UiRect::new(
constraints.viewport.x + constraints.viewport_rect.x,
constraints.viewport.y + constraints.viewport_rect.y,
constraints.viewport_rect.width,
constraints.viewport_rect.height,
);
ScrollAttachmentResolution {
mode: ScrollAttachmentMode::Fixed,
rect,
delta: UiPoint::new(rect.x - normal_rect.x, rect.y - normal_rect.y),
}
}
}
}
pub fn resolve_sticky_rect(
normal_rect: UiRect,
constraints: StickyConstraints,
) -> ScrollAttachmentResolution {
let mut x = normal_rect.x;
let mut y = normal_rect.y;
if let Some(left) = constraints.edges.left {
x = x.max(constraints.scrollport.x + left.max(0.0));
}
if let Some(right) = constraints.edges.right {
x = x.min(constraints.scrollport.right() - right.max(0.0) - normal_rect.width);
}
if let Some(top) = constraints.edges.top {
y = y.max(constraints.scrollport.y + top.max(0.0));
}
if let Some(bottom) = constraints.edges.bottom {
y = y.min(constraints.scrollport.bottom() - bottom.max(0.0) - normal_rect.height);
}
x = clamp_axis(
x,
constraints.containing_block.x,
constraints.containing_block.right() - normal_rect.width,
);
y = clamp_axis(
y,
constraints.containing_block.y,
constraints.containing_block.bottom() - normal_rect.height,
);
let rect = UiRect::new(x, y, normal_rect.width, normal_rect.height);
let delta = UiPoint::new(rect.x - normal_rect.x, rect.y - normal_rect.y);
ScrollAttachmentResolution {
mode: if point_has_delta(delta) {
ScrollAttachmentMode::Stuck
} else {
ScrollAttachmentMode::Flow
},
rect,
delta,
}
}
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum ScrollbarVisibility {
Auto,
Always,
Hidden,
}
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct ScrollbarPolicy {
pub visibility: ScrollbarVisibility,
pub thickness: f32,
pub min_thumb_length: f32,
}
impl ScrollbarPolicy {
pub const DEFAULT: Self = Self {
visibility: ScrollbarVisibility::Auto,
thickness: 10.0,
min_thumb_length: 18.0,
};
}
impl Default for ScrollbarPolicy {
fn default() -> Self {
Self::DEFAULT
}
}
pub fn scrollbar_thumb_rect(
scroll: ScrollState,
track: UiRect,
axis: ScrollAxis,
policy: ScrollbarPolicy,
) -> Option<UiRect> {
if matches!(policy.visibility, ScrollbarVisibility::Hidden) {
return None;
}
let viewport = axis.size_value(scroll.viewport_size);
let content = axis.size_value(scroll.content_size);
if content <= viewport && matches!(policy.visibility, ScrollbarVisibility::Auto) {
return None;
}
let track_length = axis.rect_end(track) - axis.rect_start(track);
if track_length <= f32::EPSILON {
return None;
}
let max_offset = axis.value(scroll.max_offset());
let ratio = if viewport <= f32::EPSILON || content <= viewport {
1.0
} else {
(viewport / content).clamp(0.0, 1.0)
};
let thumb_length = (track_length * ratio).max(policy.min_thumb_length.min(track_length));
let travel = (track_length - thumb_length).max(0.0);
let offset_ratio = if max_offset <= f32::EPSILON {
0.0
} else {
(axis.value(scroll.offset) / max_offset).clamp(0.0, 1.0)
};
match axis {
ScrollAxis::Horizontal => Some(UiRect::new(
track.x + travel * offset_ratio,
track.y,
thumb_length,
policy.thickness.min(track.height),
)),
ScrollAxis::Vertical => Some(UiRect::new(
track.x,
track.y + travel * offset_ratio,
policy.thickness.min(track.width),
thumb_length,
)),
}
}
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct KineticScrollConfig {
pub deceleration: f32,
pub min_velocity: f32,
}
impl KineticScrollConfig {
pub const DEFAULT: Self = Self {
deceleration: 2800.0,
min_velocity: 4.0,
};
}
impl Default for KineticScrollConfig {
fn default() -> Self {
Self::DEFAULT
}
}
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct KineticScrollState {
pub velocity: UiPoint,
pub active: bool,
}
impl KineticScrollState {
pub const IDLE: Self = Self {
velocity: UiPoint::new(0.0, 0.0),
active: false,
};
pub const fn new(velocity: UiPoint) -> Self {
Self {
velocity,
active: true,
}
}
}
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct KineticScrollStep {
pub state: KineticScrollState,
pub delta: UiPoint,
}
pub fn step_kinetic_scroll(
state: KineticScrollState,
elapsed_seconds: f32,
config: KineticScrollConfig,
) -> KineticScrollStep {
if !state.active || elapsed_seconds <= 0.0 || !elapsed_seconds.is_finite() {
return KineticScrollStep {
state,
delta: UiPoint::new(0.0, 0.0),
};
}
let next_velocity = UiPoint::new(
decay_velocity(state.velocity.x, elapsed_seconds, config),
decay_velocity(state.velocity.y, elapsed_seconds, config),
);
let delta = UiPoint::new(
(state.velocity.x + next_velocity.x) * 0.5 * elapsed_seconds,
(state.velocity.y + next_velocity.y) * 0.5 * elapsed_seconds,
);
let active =
next_velocity.x.abs() > config.min_velocity || next_velocity.y.abs() > config.min_velocity;
KineticScrollStep {
state: KineticScrollState {
velocity: if active {
next_velocity
} else {
UiPoint::new(0.0, 0.0)
},
active,
},
delta,
}
}
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum ScrollSyncMode {
ExactOffset,
Proportional,
}
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct ScrollSyncSurface {
pub node: UiNodeId,
pub state: ScrollState,
}
impl ScrollSyncSurface {
pub const fn new(node: UiNodeId, state: ScrollState) -> Self {
Self { node, state }
}
}
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct ScrollSyncUpdate {
pub node: UiNodeId,
pub offset_before: UiPoint,
pub offset_after: UiPoint,
}
#[derive(Debug, Clone, PartialEq)]
pub struct ScrollSyncPlan {
pub updates: Vec<ScrollSyncUpdate>,
}
pub fn synchronize_scroll_surfaces(
source: ScrollSyncSurface,
followers: &[ScrollSyncSurface],
axes: ScrollAxes,
mode: ScrollSyncMode,
) -> ScrollSyncPlan {
let source_max = source.state.max_offset();
let source_progress_x = scroll_progress(source.state.offset.x, source_max.x);
let source_progress_y = scroll_progress(source.state.offset.y, source_max.y);
let updates = followers
.iter()
.filter_map(|follower| {
let follower_max = follower.state.max_offset();
let mut offset = follower.state.offset;
if axes.horizontal && follower.state.axes.horizontal {
offset.x = match mode {
ScrollSyncMode::ExactOffset => source.state.offset.x,
ScrollSyncMode::Proportional => follower_max.x * source_progress_x,
};
}
if axes.vertical && follower.state.axes.vertical {
offset.y = match mode {
ScrollSyncMode::ExactOffset => source.state.offset.y,
ScrollSyncMode::Proportional => follower_max.y * source_progress_y,
};
}
offset = UiPoint::new(
clamp_axis(offset.x, 0.0, follower_max.x),
clamp_axis(offset.y, 0.0, follower_max.y),
);
(offset != follower.state.offset).then_some(ScrollSyncUpdate {
node: follower.node,
offset_before: follower.state.offset,
offset_after: offset,
})
})
.collect();
ScrollSyncPlan { updates }
}
pub fn content_viewport_rect(scroll: ScrollState) -> UiRect {
UiRect::new(
finite_value(scroll.offset.x),
finite_value(scroll.offset.y),
scroll.viewport_size.width.max(0.0),
scroll.viewport_size.height.max(0.0),
)
}
fn reveal_axis_offset(
current: f32,
viewport_length: f32,
max_offset: f32,
target_start: f32,
target_end: f32,
alignment: RevealAlignment,
) -> f32 {
let viewport_end = current + viewport_length;
let offset = match alignment {
RevealAlignment::Nearest => {
if target_start < current {
target_start
} else if target_end > viewport_end {
target_end - viewport_length
} else {
current
}
}
RevealAlignment::Start => target_start,
RevealAlignment::Center => (target_start + target_end - viewport_length) * 0.5,
RevealAlignment::End => target_end - viewport_length,
};
clamp_axis(offset, 0.0, max_offset)
}
fn compare_anchor_candidate(
left: (&ScrollAnchorCandidate, f32),
right: (&ScrollAnchorCandidate, f32),
) -> Ordering {
left.0
.priority
.cmp(&right.0.priority)
.then_with(|| left.1.total_cmp(&right.1))
.then_with(|| right.0.order.cmp(&left.0.order))
}
fn decay_velocity(value: f32, elapsed_seconds: f32, config: KineticScrollConfig) -> f32 {
if value.abs() <= config.min_velocity {
return 0.0;
}
let deceleration = config.deceleration.max(0.0) * elapsed_seconds;
let decayed = (value.abs() - deceleration).max(0.0);
value.signum() * decayed
}
fn scroll_progress(offset: f32, max_offset: f32) -> f32 {
if max_offset <= f32::EPSILON {
0.0
} else {
(offset / max_offset).clamp(0.0, 1.0)
}
}
fn rect_area(rect: UiRect) -> f32 {
rect.width.max(0.0) * rect.height.max(0.0)
}
fn clamp_axis(value: f32, min: f32, max: f32) -> f32 {
let value = finite_value(value);
let min = finite_value(min);
let max = finite_value(max);
if max < min {
return min;
}
value.clamp(min, max)
}
fn finite_point(point: UiPoint) -> UiPoint {
UiPoint::new(finite_value(point.x), finite_value(point.y))
}
fn finite_value(value: f32) -> f32 {
if value.is_finite() {
value
} else {
0.0
}
}
fn point_has_delta(point: UiPoint) -> bool {
point.x.abs() > f32::EPSILON || point.y.abs() > f32::EPSILON
}
#[cfg(test)]
mod tests {
use super::*;
fn scroll_state(
axes: ScrollAxes,
offset: UiPoint,
viewport_size: UiSize,
content_size: UiSize,
) -> ScrollState {
ScrollState {
axes,
offset,
viewport_size,
content_size,
}
}
#[test]
fn nested_scroll_transfer_chains_boundary_delta_to_parent() {
let inner = NestedScrollCandidate::new(
UiNodeId(2),
scroll_state(
ScrollAxes::VERTICAL,
UiPoint::new(0.0, 80.0),
UiSize::new(100.0, 100.0),
UiSize::new(100.0, 200.0),
),
);
let outer = NestedScrollCandidate::new(
UiNodeId(1),
scroll_state(
ScrollAxes::VERTICAL,
UiPoint::new(0.0, 10.0),
UiSize::new(100.0, 100.0),
UiSize::new(100.0, 300.0),
),
);
let plan = arbitrate_nested_scroll(UiPoint::new(0.0, 70.0), &[inner, outer]);
assert_eq!(plan.changed_nodes(), vec![UiNodeId(2), UiNodeId(1)]);
assert_eq!(plan.steps[0].consumed_delta, UiPoint::new(0.0, 20.0));
assert_eq!(plan.steps[0].overscroll_delta, UiPoint::new(0.0, 50.0));
assert_eq!(plan.steps[1].consumed_delta, UiPoint::new(0.0, 50.0));
assert_eq!(
plan.offset_after(UiNodeId(2)),
Some(UiPoint::new(0.0, 100.0))
);
assert_eq!(
plan.offset_after(UiNodeId(1)),
Some(UiPoint::new(0.0, 60.0))
);
assert_eq!(plan.remaining_delta, UiPoint::new(0.0, 0.0));
}
#[test]
fn nested_scroll_transfer_respects_contained_overscroll() {
let inner = NestedScrollCandidate::new(
UiNodeId(2),
scroll_state(
ScrollAxes::VERTICAL,
UiPoint::new(0.0, 100.0),
UiSize::new(100.0, 100.0),
UiSize::new(100.0, 200.0),
),
)
.overscroll(OverscrollPolicy::CONTAIN);
let outer = NestedScrollCandidate::new(
UiNodeId(1),
scroll_state(
ScrollAxes::VERTICAL,
UiPoint::new(0.0, 0.0),
UiSize::new(100.0, 100.0),
UiSize::new(100.0, 300.0),
),
);
let plan = arbitrate_nested_scroll(UiPoint::new(0.0, 40.0), &[inner, outer]);
assert_eq!(plan.steps.len(), 1);
assert_eq!(plan.blocked_delta, UiPoint::new(0.0, 40.0));
assert_eq!(plan.remaining_delta, UiPoint::new(0.0, 0.0));
assert_eq!(plan.offset_after(UiNodeId(1)), None);
}
#[test]
fn scroll_anchoring_preserves_visible_anchor_position() {
let scroll = scroll_state(
ScrollAxes::VERTICAL,
UiPoint::new(0.0, 100.0),
UiSize::new(200.0, 80.0),
UiSize::new(200.0, 600.0),
);
let anchor = ScrollAnchorCandidate::new(
UiNodeId(4),
UiRect::new(0.0, 130.0, 100.0, 20.0),
UiRect::new(0.0, 180.0, 100.0, 20.0),
)
.priority(10);
let adjustment = apply_scroll_anchor(scroll, &[anchor]);
assert_eq!(adjustment.anchor, Some(UiNodeId(4)));
assert_eq!(adjustment.offset_before, UiPoint::new(0.0, 100.0));
assert_eq!(adjustment.offset_after, UiPoint::new(0.0, 150.0));
assert_eq!(adjustment.delta, UiPoint::new(0.0, 50.0));
}
#[test]
fn sticky_and_fixed_content_resolve_against_scrollport_and_viewport() {
let normal = UiRect::new(12.0, 80.0, 120.0, 30.0);
let sticky = resolve_scroll_attachment(
normal,
ScrollAttachment::Sticky(StickyConstraints::new(
UiRect::new(0.0, 100.0, 200.0, 80.0),
UiRect::new(0.0, 0.0, 200.0, 240.0),
StickyEdges::top(8.0),
)),
);
assert_eq!(sticky.mode, ScrollAttachmentMode::Stuck);
assert_eq!(sticky.rect, UiRect::new(12.0, 108.0, 120.0, 30.0));
assert_eq!(sticky.delta, UiPoint::new(0.0, 28.0));
let fixed = resolve_scroll_attachment(
normal,
ScrollAttachment::Fixed(FixedConstraints::new(
UiRect::new(20.0, 40.0, 300.0, 200.0),
UiRect::new(8.0, 12.0, 120.0, 30.0),
)),
);
assert_eq!(fixed.mode, ScrollAttachmentMode::Fixed);
assert_eq!(fixed.rect, UiRect::new(28.0, 52.0, 120.0, 30.0));
}
#[test]
fn reveal_and_sync_helpers_plan_deterministic_offsets() {
let scroll = scroll_state(
ScrollAxes::BOTH,
UiPoint::new(10.0, 20.0),
UiSize::new(100.0, 80.0),
UiSize::new(300.0, 240.0),
);
let reveal = reveal_rect_into_view(
scroll,
UiRect::new(150.0, 130.0, 20.0, 30.0),
RevealOptions::nearest().margin(ScrollInsets::uniform(4.0)),
);
assert_eq!(reveal.offset_after, UiPoint::new(74.0, 84.0));
assert!(reveal.changed());
let follower = ScrollSyncSurface::new(
UiNodeId(9),
scroll_state(
ScrollAxes::VERTICAL,
UiPoint::new(0.0, 0.0),
UiSize::new(100.0, 50.0),
UiSize::new(100.0, 250.0),
),
);
let plan = synchronize_scroll_surfaces(
ScrollSyncSurface::new(UiNodeId(8), scroll),
&[follower],
ScrollAxes::VERTICAL,
ScrollSyncMode::Proportional,
);
assert_eq!(plan.updates.len(), 1);
assert_eq!(plan.updates[0].offset_after, UiPoint::new(0.0, 25.0));
}
}