Trait Viewport 

pub trait Viewport: Widget {
    // Required methods
    fn content_size(&self) -> Size;
    fn draw_with_offset(&self, draw: DrawCx<'_>, viewport: Rect, offset: Offset);

    // Provided methods
    fn set_offset(
        &mut self,
        cx: &mut SizeCx<'_>,
        viewport: Rect,
        offset: Offset,
    ) { ... }
    fn update_offset(
        &mut self,
        cx: &mut ConfigCx<'_>,
        data: &Self::Data,
        viewport: Rect,
        offset: Offset,
    ) { ... }
    fn try_probe_with_offset(&self, coord: Coord, offset: Offset) -> Option<Id> { ... }
}

Layout routines for scrollable content

A Viewport supports content larger than its assigned rect (the rect passed to Layout::set_rect). This rect is considered the viewport through which content may be viewed (approximately: see Self::draw_with_offset).

If the parent widget supports scrolling over contents implementing Viewport, it should call Viewport::draw_with_offset instead of Layout::draw.

It is intended that the widget implementing this trait is the child of some parent widget which supports scrolling through event handling and provision of a scroll offset, and that this parent uses the methods of this trait where applicable (see below). In case the parent does not support scrolling, the widget should remain usable (but with only a subset of content being accessible).

Required Methods

fn content_size(&self) -> Size

Get content size

When the content size is larger than the viewport, content becomes scrollable with a maximum offset of content_size - viewport_size.

Calling

This method is called during sizing.

fn draw_with_offset(&self, draw: DrawCx<'_>, viewport: Rect, offset: Offset)

Draw with a scroll offset

Drawing should be clamped to the given viewport. This viewport may be the same as Layout::rect but is allowed to be slightly different; for example EditBox passes a larger Rect to allow drawing in the margin allocated between its frame and content.

The offset should be the same as that used by the parent widget in Tile::translation.

Effectively, content is drawn at position self.rect().pos - offset but clamped to viewport.

Calling

This method should be called instead of Layout::draw by compatible parent widgets.

Implementation

Method modification

The #[widget] macro injects a call to DrawCx::set_id into this method where possible, allowing correct detection of disabled and highlight states.

This method modification should never cause issues (besides the implied limitation that widgets cannot easily detect a parent’s state while being drawn).

Provided Methods

fn set_offset(&mut self, cx: &mut SizeCx<'_>, viewport: Rect, offset: Offset)

Set the scroll offset

The viewport and offset parameters are the same as those of Viewport::draw_with_offset.

Calling

This method should be called immediately after Layout::set_rect (unless it’s known that the implementation doesn’t use this method).

Implementation

This method only needs to do anything in cases where only a subset of content is prepared.

fn update_offset( &mut self, cx: &mut ConfigCx<'_>, data: &Self::Data, viewport: Rect, offset: Offset, )

Update the scroll offset

The viewport and offset parameters are the same as those of Viewport::draw_with_offset.

Calling

This method should be called whenever the scroll offset changes to allow preparation of content (unless it’s known that the implementation doesn’t use this method). It must be called before drawing and event handling operations using this new offset.

Implementation

This method only needs to do anything in cases where only a subset of content is prepared.

fn try_probe_with_offset(&self, coord: Coord, offset: Offset) -> Option<Id>

Probe a coordinate for a widget’s Id

Calling

This method should be called instead of Tile::try_probe.

Implementation

The default implementation will normally suffice. It calls Events::probe with coord + offset when self.rect().contains(coord).

Implementors

impl<W> Viewport for Align<W>

where W: Viewport + Widget,

impl<W> Viewport for Pack<W>

where W: Viewport + Widget,