Struct ScrollPhysics 

pub struct ScrollPhysics {

    pub offset_y: f32,
    pub velocity_y: f32,
    pub offset_x: f32,
    pub velocity_x: f32,
    pub state: ScrollState,
    pub content_height: f32,
    pub viewport_height: f32,
    pub content_width: f32,
    pub viewport_width: f32,
    pub config: ScrollConfig,
    pub scrollbar_state: ScrollbarState,
    pub scrollbar_opacity: f32,
    pub area_hovered: bool,
    pub idle_time: f32,
    pub thumb_drag_start_y: f32,
    pub thumb_drag_start_x: f32,
    pub thumb_drag_start_scroll_y: f32,
    pub thumb_drag_start_scroll_x: f32,
    /* private fields */
}

Internal physics state for scroll animation

Fields

offset_y: f32

Current vertical scroll offset (negative = scrolled down)

velocity_y: f32

Current vertical velocity (pixels per second)

offset_x: f32

Current horizontal scroll offset (negative = scrolled right)

velocity_x: f32

Current horizontal velocity (pixels per second)

state: ScrollState

Current FSM state

content_height: f32

Content height (calculated from children)

viewport_height: f32

Viewport height

content_width: f32

Content width (calculated from children)

viewport_width: f32

Viewport width

config: ScrollConfig

Configuration

scrollbar_state: ScrollbarState

Current scrollbar interaction state

scrollbar_opacity: f32

Current scrollbar opacity (0.0 to 1.0, animated)

area_hovered: bool

Whether the scroll area is being hovered

idle_time: f32

Time accumulator since last scroll activity (seconds)

thumb_drag_start_y: f32

Vertical scrollbar thumb drag start position (mouse Y)

thumb_drag_start_x: f32

Horizontal scrollbar thumb drag start position (mouse X)

thumb_drag_start_scroll_y: f32

Scroll offset at drag start (Y)

thumb_drag_start_scroll_x: f32

Scroll offset at drag start (X)

Implementations

impl ScrollPhysics

pub fn new(config: ScrollConfig) -> ScrollPhysics

Create new physics with given config

pub fn with_scheduler( config: ScrollConfig, scheduler: &Arc<Mutex<AnimationScheduler>>, ) -> ScrollPhysics

Create new physics with scheduler for animation-driven bounce

pub fn set_scheduler(&mut self, scheduler: &Arc<Mutex<AnimationScheduler>>)

Set the animation scheduler (for spring-based bounce animation)

pub fn min_offset_y(&self) -> f32

Maximum vertical scroll offset (0 = top edge)

pub fn max_offset_y(&self) -> f32

Minimum vertical scroll offset (negative, at bottom edge)

pub fn min_offset_x(&self) -> f32

Maximum horizontal scroll offset (0 = left edge)

pub fn max_offset_x(&self) -> f32

Minimum horizontal scroll offset (negative, at right edge)

pub fn is_overscrolling_y(&self) -> bool

Check if currently overscrolling vertically (past bounds)

pub fn is_overscrolling_x(&self) -> bool

Check if currently overscrolling horizontally (past bounds)

pub fn is_overscrolling(&self) -> bool

Check if currently overscrolling in any direction

pub fn overscroll_amount_y(&self) -> f32

Get amount of vertical overscroll (positive at top, negative at bottom)

pub fn overscroll_amount_x(&self) -> f32

Get amount of horizontal overscroll (positive at left, negative at right)

pub fn apply_scroll_delta(&mut self, delta_x: f32, delta_y: f32)

Apply scroll delta (from user input)

Note: On macOS, the system already applies momentum physics to scroll events, so we don’t need to track velocity or apply our own momentum. We just apply the delta directly with bounds clamping.

When bouncing, we ignore momentum scroll events - the spring animation takes over and drives the position back to bounds.

pub fn apply_touch_scroll_delta( &mut self, delta_x: f32, delta_y: f32, current_time: f64, )

Apply scroll delta from touch input with velocity tracking

This is used on mobile platforms where we need to track velocity ourselves for momentum scrolling (unlike macOS which provides it).

current_time is in milliseconds (from elapsed_ms()).

pub fn on_scroll_end(&mut self)

Called when scroll gesture ends - start momentum/bounce

pub fn on_gesture_end(&mut self)

Called when scroll gesture ends (finger lifted from trackpad)

If overscrolling, start bounce immediately for snappy feedback. The user expects the elastic snap-back to begin the moment they release.

pub fn tick(&mut self, dt: f32) -> bool

Update scroll offsets from animation scheduler springs

Returns true if still animating, false if settled. This reads spring values from the AnimationScheduler which ticks them on a background thread at 120fps.

dt is delta time in seconds since last tick.

pub fn is_animating(&self) -> bool

Check if animation is active

pub fn set_direction(&mut self, direction: ScrollDirection)

Set the scroll direction

pub fn scroll_to_animated(&mut self, target_x: f32, target_y: f32)

Animate scroll to a target offset using spring physics

This provides smooth animated scrolling instead of instant jumps. The spring configuration uses a snappy feel for quick but smooth transitions.

pub fn on_area_hover_enter(&mut self)

Called when scroll area is hovered

pub fn on_area_hover_leave(&mut self)

Called when scroll area hover ends

pub fn on_scrollbar_track_hover(&mut self)

Called when scrollbar track is hovered

pub fn on_scrollbar_thumb_hover(&mut self)

Called when scrollbar thumb is hovered

pub fn on_scrollbar_hover_leave(&mut self)

Called when scrollbar hover ends (mouse leaves track/thumb)

pub fn on_scrollbar_drag_start(&mut self, mouse_x: f32, mouse_y: f32)

Called when scrollbar thumb drag starts

Arguments

• mouse_x - Current mouse X position
• mouse_y - Current mouse Y position

pub fn on_scrollbar_drag(&mut self, mouse_x: f32, mouse_y: f32) -> (f32, f32)

Called during scrollbar thumb drag

Arguments

• mouse_x - Current mouse X position
• mouse_y - Current mouse Y position

Returns

New scroll offset (x, y) that should be applied

pub fn on_scrollbar_drag_end(&mut self)

Called when scrollbar thumb drag ends

pub fn on_scroll_activity(&mut self)

Called when scroll activity occurs (shows scrollbar in Auto mode)

pub fn tick_scrollbar(&mut self, dt: f32) -> bool

Tick scrollbar animation (call from main tick)

Arguments

• dt - Delta time in seconds

Returns

true if scrollbar animation is still active

pub fn thumb_dimensions_y(&self) -> (f32, f32)

Calculate thumb dimensions for vertical scrollbar

Returns

(thumb_height, thumb_y_position) in pixels

pub fn thumb_dimensions_x(&self) -> (f32, f32)

Calculate thumb dimensions for horizontal scrollbar

Returns

(thumb_width, thumb_x_position) in pixels

pub fn can_scroll_y(&self) -> bool

Check if content is scrollable vertically

pub fn can_scroll_x(&self) -> bool

Check if content is scrollable horizontally

pub fn hit_test_scrollbar( &self, local_x: f32, local_y: f32, ) -> ScrollbarHitResult

Hit test a point against the scrollbar

Takes coordinates relative to the scroll container (local space). Returns what part of the scrollbar (if any) the point is over.

pub fn on_scrollbar_pointer_down(&mut self, local_x: f32, local_y: f32) -> bool

Handle pointer down on scrollbar

Returns true if the event was handled (pointer was over scrollbar).

pub fn on_scrollbar_pointer_move( &mut self, local_x: f32, local_y: f32, ) -> Option<(f32, f32)>

Handle pointer move during scrollbar drag

Returns Some((new_offset_x, new_offset_y)) if dragging, None otherwise.

pub fn on_scrollbar_pointer_up(&mut self)

Handle pointer up during scrollbar drag

pub fn scrollbar_render_info(&self) -> ScrollbarRenderInfo

Get current scrollbar render info

Trait Implementations

impl Default for ScrollPhysics

fn default() -> ScrollPhysics

Returns the “default value” for a type.