Struct kas_widgets::ScrollComponent

pub struct ScrollComponent { /* fields omitted */ }

Logic for a scroll region

This struct handles some scroll logic. It does not provide scrollbars.

Implementations

impl ScrollComponent

pub fn max_offset(&self) -> Offset

Get the maximum offset

Note: the minimum offset is always zero.

pub fn offset(&self) -> Offset

Get the current offset

To translate a coordinate from the outer region to a coordinate of the scrolled region, add this offset.

pub fn set_sizes(&mut self, window_size: Size, content_size: Size) -> TkAction

Set sizes:

• window_size: size of scroll region on the outside
• content_size: size of scroll region on the inside (usually larger)

Like Self::set_offset this generates a TkAction due to potential change in offset. In practice the caller will likely be performing all required updates regardless and the return value can be safely ignored.

pub fn set_offset(&mut self, offset: Offset) -> TkAction

Set the scroll offset

The offset is clamped to the available scroll range. Returns TkAction::empty() if the offset is identical to the old offset, or TkAction::REGION_MOVED if the offset changes.

pub fn set_scroll_rate(&mut self, rate: f32)

Set the scroll rate

This affects how fast arrow keys and the mouse wheel scroll (but not pixel offsets, as from touch devices supporting smooth scrolling).

pub fn offset_event(&self, event: Event) -> Event

Apply offset to an event being sent to the scrolled child

pub fn focus_rect(&mut self, rect: Rect, window_rect: Rect) -> (Rect, TkAction)

Handle Response::Focus

Inputs and outputs:

• rect: the focus rect
• window_rect: the rect of the scroll window
• returned Rect: the focus rect, adjusted for scroll offset; normally this should be returned via another Response::Focus
• returned TkAction: action to pass to the event manager

pub fn scroll_by_event<PS: FnMut(PressSource, WidgetId, Coord)>(
    &mut self,
    event: Event,
    window_size: Size,
    on_press_start: PS
) -> (TkAction, Response<VoidMsg>)

Use an event to scroll, if possible

Handles keyboard (Home/End, Page Up/Down and arrow keys), mouse wheel and touchpad scroll events. Also handles mouse/touch drag events if the on_press_start closure activates a mouse/touch grab.

Behaviour on Event::PressStart is configurable: the closure is called on this event and should call Manager::request_grab if the press should scroll by drag. This allows control of which mouse button(s) are used and whether any modifiers must be pressed. For example:

fn dummy_event_handler(
    id: WidgetId,
    scroll: &mut kas_widgets::ScrollComponent,
    mgr: &mut Manager,
    event: Event
)
    -> Response<Msg>
{
    let window_size = Size(100, 80);
    let (action, response) = scroll.scroll_by_event(event, window_size, |source, _, coord| {
        if source.is_primary() {
            let icon = Some(kas::event::CursorIcon::Grabbing);
            mgr.request_grab(id, source, coord, kas::event::GrabMode::Grab, icon);
        }
    });
    *mgr |= action;
    response.void_into()
}

If the returned TkAction is None, the scroll offset has not changed and the returned Response is either None or Unhandled(..). If the returned TkAction is not None, the scroll offset has been updated and the second return value is Response::None.

Trait Implementations

impl Clone for ScrollComponent

fn clone(&self) -> ScrollComponent

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for ScrollComponent

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for ScrollComponent

fn default() -> Self

Returns the “default value” for a type.

impl PartialEq<ScrollComponent> for ScrollComponent

fn eq(&self, other: &ScrollComponent) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &ScrollComponent) -> bool

This method tests for !=.

impl StructuralPartialEq for ScrollComponent