Graphical Presenter component role
Overview
Graphical Presenter is a component role, within the session, that presents multiple graphical views to the user; most commonly, views from the session’s Elements.
Although the same session component could also implement the Graphical Presenter
roll, there is a FIDL protocol, fuchsia.element.GraphicalPresenter
,
that allows a session component to delegate Graphical Presenter
responsibilities another component. This makes it possible for each component to
execute in different runtimes (such Rust versus Flutter/Dart) if needed.
Displaying element views
For Fuchsia-based products running on devices with a graphical display, a session implementation manages displayable components through the Element API. Each element renders its graphical representation in what is known as a “view”.
A session will request the Element’s view, and then pass that view to the Graphical Presenter to be displayed, along with optional Element Annotations, used to communicate product-specific presentation properties.
PresentView request {#present-view}
The session calls the GraphicalPresenter
method PresentView()
to display a
given view. PresentView()
takes:
- A
ViewSpec
, through which the session conveys where and how it wants the view to be displayed in theScenic
scene graph. - An
AnnotationController
, which is a handle to the element’s annotations, through which the presenter can update the respective element’s annotations.
In return, the caller is given a handle to
the view, as a ViewController
. The caller can destroy
the view (remove it from the display) by releasing or closing its ViewController
.
The developer guide includes an example implementation of presenting an element’s view.