Trait OffsetLayerMixin

Source

pub trait OffsetLayerMixin: ContainerLayer {
    // Required methods
    fn offset_layer_data(self: Handle<Self>, app: &App) -> &OffsetLayerData;
    fn offset_layer_data_mut(
        self: Handle<Self>,
        app: &mut App,
    ) -> &mut OffsetLayerData;

    // Provided methods
    fn as_offset_layer(self: Handle<Self>) -> AnyOffsetLayer { ... }
    fn offset(self: Handle<Self>, app: &App) -> Offset { ... }
    fn set_offset(self: Handle<Self>, app: &mut App, value: Offset) { ... }
    fn find_annotations(
        self: Handle<Self>,
        app: &App,
        result: &mut AnnotationSearch,
        local_position: Offset,
        only_first: bool,
    ) -> bool { ... }
    fn apply_transform(
        self: Handle<Self>,
        app: &App,
        child: Option<AnyLayer>,
        transform: &mut Matrix4,
    ) { ... }
    fn add_to_scene(
        self: Handle<Self>,
        app: &mut App,
        builder: &mut SceneBuilder,
    ) { ... }
}

Expand description

A layer that is displayed at an offset from its parent layer.

Offset layers are key to efficient repainting because they are created by repaint boundaries in the RenderObject tree (see RenderObject.isRepaintBoundary). When a render object that is a repaint boundary is asked to paint at given offset in a PaintingContext, the render object first checks whether it needs to repaint itself. If not, it reuses its existing OffsetLayer (and its entire subtree) by mutating its offset property, cutting off the paint walk.

Flutter’s OffsetLayer is a concrete class that TransformLayer, OpacityLayer and ImageFilterLayer extend: the bodies are here, OffsetLayer is the concrete leaf.