Struct RepaintTrigger 

pub struct RepaintTrigger { /* private fields */ }

Marks the widgets it is attached to for repaint, relayout or a pull from any thread, and wakes only their windows.

For content that changes off the UI thread: a terminal’s child printing, a background task’s progress, a status a service publishes. The producer stores the new state where the widget will read it, then requests; the widget reads it in the frame the request wakes. Requests coalesce: one wake per window until the widget has consumed the request.

• request_repaint: only what the widget paints changed. Its window redraws, and the widget alone repaints.
• request_relayout: its size or what layout reads changed. It and its ancestors relayout, also in a window that draws nothing.
• request_pull: the widget has data to take in on the UI thread whether or not it is shown, through the hook it registered with BuildContext::on_trigger_pull. A widget that is not shown takes it in without its window drawing a frame.

A relayout or a pull reaches a window that draws nothing (minimised, covered, its frames withheld by the compositor), whose event loop then runs the layout half of a frame for it; a repaint waits there for the window to draw again.

Attach it in every build() with BuildContext::attach_repaint_trigger; a rebuild or the widget’s destruction releases the attachment, and the tree’s drop releases the rest. One trigger may be attached to several widgets, in several windows. Send + Sync; a clone shares the trigger.

Do not request from paint() or a frame-tick effect: the widget would repaint at display rate. Inside an event handler, the widget’s own invalidation (EventContext::request_repaint) is cheaper.

Implementations

impl RepaintTrigger

pub fn new() -> Self

A trigger attached to nothing yet.

pub fn request_repaint(&self)

Only what the attached widgets paint changed. Each window wakes at most once until the widget’s next paint. A widget that is not painted (dormant, clipped out) keeps the request for when it is, and costs one wake until then, however many requests follow.

pub fn request_relayout(&self)

The attached widgets’ size or what layout reads changed: they and their ancestors relayout, and repaint. Each window wakes at most once until the widget’s next layout pass, and the wake reaches a window that draws nothing.

pub fn request_pull(&self)

The attached widgets have data to take in on the UI thread, shown or not: their pull hook (BuildContext::on_trigger_pull) runs in their window’s next frame. The window draws that frame when a widget with a pull pending was shown in its last one, and otherwise runs one that draws nothing. Each window wakes at most once until the hook has run. A widget with no hook is repainted as by request_repaint.

pub fn is_attached(&self) -> bool

Whether the trigger is attached to at least one live widget.

pub fn stats(&self) -> RepaintTriggerStats

What the trigger did so far.

pub fn ptr_eq(&self, other: &Self) -> bool

Whether self and other are the same trigger.

Trait Implementations

impl Clone for RepaintTrigger

fn clone(&self) -> Self

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for RepaintTrigger

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

Counters only: never takes the list lock, so it is safe to print from anywhere, while a request is in progress included.

impl Default for RepaintTrigger

fn default() -> Self

Returns the “default value” for a type.