Struct egui::Id

pub struct Id(_);

egui tracks widgets frame-to-frame using Ids.

For instance, if you start dragging a slider one frame, egui stores the sliders Id as the current active id so that next frame when you move the mouse the same slider changes, even if the mouse has moved outside the slider.

For some widgets Ids are also used to persist some state about the widgets, such as Window position or wether not a collapsing header region is open.

This implies that the Ids must be unique.

For simple things like sliders and buttons that don’t have any memory and doesn’t move we can use the location of the widget as a source of identity. For instance, a slider only needs a unique and persistent ID while you are dragging the slider. As long as it is still while moving, that is fine.

For things that need to persist state even after moving (windows, collapsing headers) the location of the widgets is obviously not good enough. For instance, a collapsing region needs to remember wether or not it is open even if the layout next frame is different and the collapsing is not lower down on the screen.

Then there are widgets that need no identifiers at all, like labels, because they have no state nor are interacted with.

Implementations

impl Id

pub fn new(source: impl Hash) -> Id

Generate a new Id by hashing some source (e.g. a string or integer).

pub fn with(self, child: impl Hash) -> Id

Generate a new Id by hashing the parent Id and the given argument.

Trait Implementations

impl Clone for Id

fn clone(&self) -> Id

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for Id

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

Formats the value using the given formatter.

impl Hash for Id

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H) where
    H: Hasher, 

Feeds a slice of this type into the given Hasher.

impl PartialEq<Id> for Id

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

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

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

This method tests for !=.

impl Copy for Id

impl Eq for Id

impl StructuralEq for Id

impl StructuralPartialEq for Id